Tropical Diseases — Chapter 45 : Intestinal Parasites

Patrick Manson

Exported from Wikisource on December 13, 2024

CHAPTER XLV

V. INTESTINAL PARASITES

1. NEMATODES

Microscopical examination of the fæces for ova of intestinal parasites.—If the fæces of the natives of warm climates, and of Europeans coming from warm climates, are systematically examined with the microscope, in a large proportion of cases they will be found to contain the ova of one or other of three species of nematode worms—Ascaris lumbricoides, Trichiuris trichiura (T. dispar), and Ankylostomum duodenale. The ova of tapeworm and of the common thread-worm (Oxyuris vermicularis) are

Fig. 168.—Ova of nematodes.

a, Strongylus subtillis; b, Ankylostomum duodenale; c, Trichiuris trichiura; d, Strongyloides starcoralis; e, Necator americanus; f, Ascaris lumbricoides; g, Ascaris lumbricoides (unfertilized).

rarely found in the stools, as these parasites do not, as a rule, part with their ova until the joints of the former, or the entire body of the latter, have left the alimentary canal; but as the three nematodes first mentioned pass their eggs directly into the bowel, these eggs habitually appear in the fæces and constitute unequivocal evidence of the presence of their respective parental forms. Occasionally the ova of hepatic and intestinal parasites, such as Schistosomum japonicum, S. mansoni, Clonorchis sinensis, Fasciola hepatica, Fasciolopsis buski, and other rarer helminths, are encountered. Without large experience the ova of the rarer parasites cannot be identified off hand; but if the practitioner has learned to recognize those of the three common species, he will at one know when he comes across the ova of any of the rarer species, and, on referring to some special work on helminthology, will have little difficulty in arriving at a correct diagnosis.

The microscopical examination of fæces for ova, though somewhat disagreeable, is by no means a difficult matter. All that is necessary, by way of preparation, is to place on the slip a minute portion of the suspected fæces—about the size of a hemp-seed—and then to apply the cover-glass, gently gliding it over the slip so as to spread out the mass in a thin, fairly uniform, and transparent layer. If the bit of fæces prove too consistent, a little water may be added so as to soften it. If the stools are loose and watery, the sediment should be taken up with a pipette and examined. It is well to make two or three preparations. The microscopical examination must, in the first instance, be made with a low power—an inch or, better, a half-inch objective. Search must be made in every part of the slide, and every suspicious body carefully scrutinized, a higher power being used if necessary. A very little practice suffices for the identification not only of the commoner ova, but of the species of parasite to which the ova belong.

The points to be attended to in the diagnosis of ova are size, shape, colour, thickness, roughness, smoothness, and markings on the surface of the shell; the presence or otherwise

Fig. 169.—Ova of trematodes.

a Schistosomum hæmatobium; b, S. mansoni; c, Heterophyes heterophyes d, Opistorchis sinensis; e, Opistorchis noverca; f, Paragonimus westermani; g, Fasciolopsis buski.

of yolk spheres, of a differentiated embryo, or, in the case of the cestodes, of the three pairs of embryonic hooklets; the existence of an operculum in the case of certain trematodes and of the broad tapeworms (Dibothriocephalus). The ova of the same species of parasite vary but slightly, and are in every instance sufficiently stable and definite for correct diagnosis.

Ova of Trichiuris trichiura (Fig. 168, c).—Of the three common nematodes mentioned—Trichiuris trichiura, Ascaris lumbricoides, and Ankylostomum duodenale—the ova of the first are the most frequently met with. They occur sometimes in enormous numbers, as many as six or eight specimens being visible in one field of an inch objective. They form a rather striking object under the microscope (Fig. 170). They are oval, measuring 51 to 54 μ by 21 to 23 μ, the ends of the long axis of the oval being slightly pointed and tipped with a little shining projection or plug. Their general appearance suggests an elongated oval tray, the projections at the poles of the ovum representing the handles of the tray. They are dark brown in colour, sharply defined, doubly outlined, and contain no differentiated embryo.

The ova of Ascaris lumbricoides (Fig. 168, f, g, and Fig. 171) are considerably larger (60 to 75 μ by 40 to 58 μ) than those of trichiuris (Fig. 168, c). They are also, as a rule, more spherical, or rather, more broadly oval; occasionally they are almost barrel-shaped. Like those of trichocephalus, they are dark brown in colour from bile-staining, but they are much less sharply and smoothly defined, possessing a coarse thick shell which is roughened by many warty excrescences. The yolk contents are not always easily made out, nor, when made out, can any sign of embryo or segmentation be discovered.

Fig. 170.—Ovum of Trichiuris trichiura, x 280. (Photograph by Dr. J. Bell.)

In certain instances, supposed to be unfertilized, the ova are smooth on the surface, the rough outer layer being almost or altogether absent.

A point of practical importance to be attended to lies in the circumstance that the rough outer layer on the shell of the ovum of ascaris is very easily detached, leaving the egg with a sharp, smooth outline suggestive of some other species of parasite. To obviate this, in mounting fæces it is well to avoid too much gliding of the cover-glass over the slip.

The ova of Ankylostomum duodenale (Fig. 168, b) contrast very markedly with both the foregoing, particularly in the matter of colour. Trichocephalus and ascaris ova are invariably dark and bile-stained; those of the ankylostomum are beautifully clear and transparent; they measure 55 μ to 65 μ by 32 μ to 43 μ; have a regular, somewhat elongated oval form, with a delicate, smooth, transparent shell, through which two, or four, or eight light-grey yolk segments can be distinctly seen. It is well to search for these ova soon after the fæces have been passed; otherwise, owing to the rapidity with which, in favourable circumstances, development proceeds, the embryo may have quitted the shell and the egg be no longer visible.

TRICHIURIS TRICHIURA (L.)

Synonyms.—Ascaris trichiura; Trichocephalus hominis; T. dispar.

Fig. 171.—Ovum of A. lumbricoides, x 250. (Photograph by Dr. J. Bell.)

Trichiuris trichiura, the whip-worm (Fig. 174), lives chiefly in the cæcum. In many countries it is present in more than half the population. It is believed to maintain its position by transfixing, pin-fashion, with its long slender neck, a superficial fold of the mucous membrane. Wichmann claims to have shown, by serial sections of the cæcum at sites where the parasites were fixed, that it is merely embedded in the mucus between the intestinal villi. According to Powell, the females very much preponderate, the proportion to males being as 466 to 1. Except that the practitioner should be familiar with the appearance of its eggs in the stool (Fig. 168, c), so that he may be able to distinguish them from those of ascaris, of ankylostomum, and of other parasites, the presence of T. trichiura is of no practical moment. So far as known, it gives rise to no serious pathological lesion; a fortunate circumstance, seeing that hitherto it has been found impossible, with any degree of certainty, to dislodge it by anthelmintics.

ASCARIS LUMBRICOIDES (L.)

Though not quite so common in tropical countries as trichiurus, the ascaris is nevertheless very common indeed, especially in children, who often harbour these loathsome creatures in enormous numbers—in dozens, or even in hundreds. In those countries, at one time or another, nearly every child gets them; so much so that, when doubt exists about the nature of some obscure affection, a dose or two of santonin often produces results which will seem to justify a diagnosis of "worms," and, for the time being, perhaps satisfy an anxious mother.

Fig. 172.—Ova of cestoda.

(After Looss.)

a, Tænia solium; b, Tænia saginata; c, Hymenolepsis nana.

Mode of infection.—The reason for the great frequency of Ascaris lumbricoides in tropical countries is probably twofold—the warmth of the climate, and the habits of the people with regard to the disposal of night-soil. In the fæces the ova exhibit no trace of segmentation or of differentiated embryo; but if placed in water, or kept moist and in a warm place, in the course of one or more months—longer or shorter according to temperature—the larva is developed, and can be seen coiled up and moving about inside the egg-shell. If such an egg is accidentally or intentionally swallowed, on arrival in the stomach the shell is dissolved away and the contained larva is set free. In a month it grows into a sexually mature animal, and, if both sexes are present, eggs in countless numbers are soon produced and appear in the fæces. Desiccation of the egg at atmospheric temperature does not destroy the larva, which will quickly revive on becoming moistened. In many warm countries night-soil is the favourite fertilizer, and is regularly collected and spread upon the fields. In this way the ova of ascaris obtain an opportunity of maturing, and thus, too, they have an opportunity of being swallowed by man. They may also be washed into drinking-water; or, becoming desiccated on the drying up of the fields, be blown about as dust; or they may become attached to fruit or vegetables. In one of these, or in similar ways, they finally reach the human stomach and there attain maturity.

This view of the life-history of A. lumbricoides was based on numerous experiments on man by Continental observers, and until recently seemed to be justified. Stewart, however, has shown that if ripe ascaris ova are fed to mice and certain other rodents, the larvæ, or a proportion of them, on being hatched out, bore their way into the liver and lungs. In the latter organs they appear in about a week's time, and, if the dose of eggs has been a large one, may cause fatal pneumonia. Stewart fed ascaris-infected mouse-dung to five pigs. Two of the experiments proved negative; in one pig a single female ascaris was found, and in the remaining two several sexually mature specimens. Stewart concludes that mice and rats serve the ascaris as intermediary host, man acquiring the infection in

Fig. 173.—Ovum of A. duodenale, x 250. (Photograph by Dr. J. Bell.)

food contaminated by the saliva of these rodents. It may be so, but further evidence is required before this conclusion can be accepted. Stewart's experiments certainly show that the larval ascaris leaves the lumen of the gut, and explain the purpose of the beak-like organ with which its cephalic end is furnished. Possibly when the larva quits the ripe egg in man it penetrates the gut and becomes encysted there or elsewhere for a time, undergoing developmental changes in anticipation of its return to the alimentary canal.

Symptoms.—In many instances the ascaris gives rise to no very noticeable symptom; in other instances it is to be credited with a number of ill-defined gastric and perhaps nervous troubles—capricious appetite, foul breath, restless sleep, peevishness, vague abdominal pains, nausea, and so forth. Sometimes the worms get into the stomach and are vomited, their appearance giving rise to no inconsiderable alarm. They may even creep up the œsophagus and into the mouth, or out by the nostrils. Cases are on record in which they caused suffocation by wandering into the rima glottidis. They have been

Fig. 174.—Trichiuris trichiura. (Magnified.)

a, Male partly embedded in the mucous membrane of the intestine; b, female.

known to enter the bile-ducts and give rise to jaundice; to penetrate the intestinal wall and escape into the peritoneum, causing peritonitis; or to burrow into the abdominal walls and cause abscess. Fortunately these accidents are of rare occurrence; their possibility, however, should be borne in mind, and, apart from other obvious considerations, ought to make us endeavour to rid patients of these troublesome guests as soon as possible. With this object in view, it was my practice in China to give my little patients, as a matter of routine, a few doses of santonin twice a year; very often the precaution ceived its justification by the appearance of one or more ascarides in the stools.

Adults, especially young adults, although to a much smaller degree than children, are liable to entertain these verminous visitors. Sometimes certain obscure dyspeptic symptoms in grown-up people will resist all treatment until three or four grains of santonin and a purgative have been administered. I had a patient once who for a long time had been troubled with unaccountable nausea. One day, while he was sitting at breakfast, the feeling of sickness came on with unusual intensity. He had to leave the table, and, after one or two retching efforts, brought up an Ascaris lumbricoides. After this he was no more troubled with nausea. It is well, therefore, when puzzled over some obscure dyspeptic condition in tropical patients, to bear the ascaris in mind. If, for some reason, it is undesirable to give santonin unnecessarily, the stools ought first to be examined with the microscope. If ova (Fig. 168, f, g) are found, a dose or two of santonin may clear up the diagnosis and cure the patient; if no ova are found, the drug may be withheld and the idea of ascarides abandoned.

Treatment.— The ascaris is readily expelled by a few grains of santonin. The dose is from ½ to 1 gr. for a child, 3 to 5 gr. for an adult. A good plan of giving the drug is to prescribe three such doses on successive nights, the first and the last dose to be followed by castor oil next morning. Patients, or mothers, ought to be warned about the peculiar effect santonin has on the urine and sometimes on the vision. I have only once seen any bad effect; in this instance a peculiar sort of intoxication, attended with delirium, which did not quite pass away for several days, followed its exhibition.

Lagochilascaris minor (Leiper, 1909) was removed from an abscess in a native of Trinidad. This species is normally an intestinal parasite, and its occurrence under the skin of man undoubtedly indicates an abnormal infection. L. major (Leiper, 1909) is found in the lion in East Africa. The male is 5 mm. by 2 mm., the female 15 mm. in length. There are three cuticular lips, separated from the body by a cuticular ring. A narrow keel-like edge of cuticle extends along either side of the hody. The two spicules are solid chitinons rods. The medial papillae number over 24 pairs; there are at least 5 pairs of postanal papillae.

ANKYLOSTOMUM DUODENALE, Dubini, 1843

Synonyms.—Anchylostomwn duodenale; Agchylostoma duodenale; Anchylostoma duodenalis; Strongyluts duodenalis; Dochmius duodenalis; Uncinaria duodenalis.

Ascaris lumbricoides, though an unpleasant parasite, cannot be considered a dangerous one, unless in very exceptional circumstances. It is otherwise with the ankylostomum; this, in many tropical countries, on account of the dangerous cachexia to which it gives rise, called ankylostomiasis, amounts to a positive curse.

Nomenclature.—The form of endemic anaemia with which this parasite is associated is of so marked a character that it has received a variety of distinctive names. Thus, in the French West Indies severe ankylostomiasis is known as cachexie aqueuse; sometimes as malcceur, or as mal d'estomac des negres; in Colombia it is called tuntun, the sufferers being known as tunientos; in Brazil it has been called oppilatio, opilaqao, and canqapo; in Europe it is sometimes known as " miner's anaemia," or " tunnel disease," the latter in allusion to the notorious St. Gothard epidemic; the form occurring in Egypt is spoken of as Egyptian chlorosis; in Ceylon it has been called "beriberi," a name which has not infrequently caused confusion with true beriberi; and, doubtless, elsewhere there are local names for this peculiar verminous anaemia.

Geographical distribution.—Since its discovery by Dubini, in 1838, the ankylostomum has been found so widely diffused that it may be said to occur in all tropical and sub-tropical countries. It occurs in Belgium, and a few years ago was found by Prof. Haldane to be the cause of an epidemic of severe anaemia in a Cornish mine. In northern countries it is rare; but it is abundantly present in the south of Europe, and in the tropical and sub-tropical regions of Asia and America; it has been ascertained to exist in North and South Queensland, Australia, and in several of the islands of the Pacific. So prevalent is it in many parts of India that, according to Dobson, quite 75 per cent. of the inhabitants are affected. In Egypt it is found at nearly every post-mortem examination; and there the anæmia it gives rise to is one of the most common causes for the rejection of recruits for the army. Thornhill regarded its ravages in Ceylon as far more serious than those of cholera; this, not on account of the number of deaths it causes directly, but on account of the vast numbers affected, the chronic nature of the disease, and the aggregate mortality, direct, and especially indirect, for which it is responsible.

Fig. 175.—Ankylostomum duodenale (natural size).

(Dubini.)

a, Male; b, female.

The parasite (Fig. 175).—The normal habitat of A. duodenale is the small intestine of man, particularly the jejunum, less so the duodenum, rarely the ileum or lower reaches of the alimentary canal; very occasionally it is found in the stomach. In these situations it attaches itself by means of its powerful buccal armature to the mucous membrane, from the blood of which it obtains a plentiful supply of nourishment. It is supposed to shift its hold from time to time, the abandoned bite continuing to ooze blood for a short period. It is said to be very prodigal of the blood it imbibes, the red corpuscles passing through its alimentary canal unchanged, the plasma alone being utilized.

The male and female ankylostomes—present generally in the proportion of one of the former to three of the latter—do not differ so much in size as is the case with many of the other nematodes. The male (Fig. 177) measures from 8 to 11 mm. in length by 0·4-0·5 mm. in breadth; the female (Fig. 176) 10-13 mm. in length by 1 mm. in breadth. Both sexes are cylindrical in form, white when they are alive, grey when dead, reddish brown when full of blood. In both sexes the posterior end is the broadest part, whence the body tapers forward to a narrow neck ending in a powerfully armed, bulging, and distinct mouth capsule (Fig. 178, B). The margin of this remarkable organ is furnished with four strong, clawlike hooks—two on each side of the ventral line, and two conical teeth one on each side of the dorsal line. The tail of the female is conical, ending in a short delicate spine; the anus is subterminal, and the vagina opens on the ventral surface at the beginning of the posterior third of the body. The tail of the male is provided with a large, umbrella-like, trilobate bursa (Fig. 178, A) possessing eleven ribs. Two long and very delicate spicules project from the cloaca, which opens at the bottom of the bursa. Owing to the relative positions of the sexual openings, the worms in conjugation look like the Greek .

Reproduction and mode of infection.—The female ankylostomes produce a prodigious and never-ending stream of eggs (Fig. 168, b), which pass out in the fæces. As already stated, while in the body of the host the development of the embryo does not advance very far; but on leaving the human host it proceeds, in suitable circumstances, so rapidly that in one to two days a rhabditiform embryo (0·2 mm. by 0·014 mm.) is born. This minute organism (Fig. 179) is very active, voraciously devouring what organic matter it can find and, for a week, growing rapidly, to 0·56 mm. by 0·024 mm. (Fig. 180).

Fig. 176.—A. duodenale, female. (After Looss.      )

Fig. 177.—A. duodenale, male. (After Looss.)

During this time it moults twice. After the second moulting it passes into a torpid condition, in which it ceases to eat, and its growth is suspended. In this state it may live for weeks or months, moving about more or less languidly in muddy water, in mud, or in damp earth. Should chance so determine, it is finally transferred to the human alimentary canal, either in muddy drinking-water, or in the mud or dirt adhering to the hands or the food dishes of the agriculturist, the brick-maker, or other operative engaged in handling the soil; or, it may be, in earth deliberately eaten by the geophagist and children. Arrived in its final host, after moulting again at the end of five weeks (Leichtenstern), it acquires sexual characters and the permanent adult form.

Fig. 178.—A. duodenale. (After Looss.)

A, Bursa; B, head.

Until recently this was believed to be the only method of infection, but Looss has shown that the parasite may reach the intestinal canal by another route. In making some experiments with "cultures" of ankylostomum larvæ, Looss inadvertently allowed the culture to come into contact with his hand. This was followed by redness and irritation of the skin of the part and, subsequently, by well-marked ankylostomiasis; the sequence of events suggesting that the larvæ in the cultures had penetrated the skin of his hand and so attained the bowel. On another occasion Looss repeated this experiment on a human leg, an hour before its amputation. Sections of the skin showed the larvæ in the hair-follicles, and some had traversed the hair papillæ and lay in the connective tissue around the follicles. Subsequently, other experiments on dogs and men established the fact that the embryos of A. duodenale can enter the skin, and that they do so as a first step towards reaching the intestine. From the subcutaneous

Fig. 179.—A. duodenale.

a, Young larva; b      , head.

Fig. 180.—A. duodenale, mature larva.

(Partly after Looss.)

tissue they enter the blood-vessels and lymphatics, and by this channel are passively transferred to the lungs. Here they leave the capillaries, enter the air vesicles, and thence along the bronchi and trachea pass into the œsophagus, and so to the stomach. It has been conjectured that during this passage the larva acquires the power of resisting the action of the gastric juice. If this be so, then the indirect route described must be the only way by which the ankylostome can arrive at maturity. The success of feeding experiments, which hitherto has been regarded as proof that the parasite passed directly to the stomach, may be attributed to the passage of the larvae into the wall of the œsophagus while the dose of larva-laden material was being swallowed.

Sambon has suggested that a proportion of the ankylostomum larvae pass directly, via the blood-stream, from skin to intestine. To test this suggestion, Fülleborn and Schilling-Torgau in one set of dogs divided the œsophagus, stitching the lower divided end to the skin; in another set of dogs a cannula was inserted into the trachea so that the bronchial secretion could not pass into the œœsophagus. The dogs were then infected with A. caninum. After a time both sets of dogs gave evidence of small-intestine infections of ankylostomes. Sambon's suggestion, therefore, is to some extent well founded.

The duration of the life of A. duodenale in the intestine has not been determined; some state it in months, others in years (Sonsino)— one to three. On account of liability to re-infection, this point, an important one as affecting prognosis, is difficult to determine.

Giles holds that A. duodenale may become sexually mature while outside the human body and in the free state; in other words, that it is heterogenetic, an abundant supply of food favouring non-parasitic multiplication. His observations, while supported by Ozzard, Annett, Ross, and Sandwith, are opposed by Looss, who points out that probably other free-living

nematodes have been mistaken for the species in question; that in fact the illustrations in Giles's report represent three males belonging to different species and characterized by an entirely different configuration of the posterior extremity.

NECATOR AMERICANUS, Stiles, 1902

Synonym.—Uncinaria americana.

History.—In May, 1902, Stiles discovered that ankylostomiasis in America was not, as a rule, due

Male[1]Female.

Fig. 181.—Necator americanus. (After Placencia.)

to Ankylostomum duodenale, but to a new species of the closely allied genus Necator, which he named Necator americanus. Geographical distribution.—So far as determined, the distribution of N. americanus includes in America—Virginia, North and South Carolina, Georgia, Florida, Alabama, Texas, Porto Rico, Cuba, and Brazil. It has been found by Looss in pygmies from Central Africa, and by others in India (Assam, Burma, Ceylon), West Africa, Rhodesia, Fiji, the Philippines, and elsewhere. Probably it is as widely diffused as A. duodenale; and in certain localities, Fjii and Ceylon for example, it is the commonest form of ankylostomum encountered.

Fig. 182.—Necator americanus.

A, Bursa;       B, head.

Fig. 183.—Necator americanus, head.

(After Looss.)

The parasite (Figs. 181-3).—N. americanus can be readily distinguished from Ankylostomum duodenale; it is a shorter and more slender worm. The male measures from 7 to 9 mm. in length by 0·3 to 0·35 mm. in diameter; the female, 9 to 11 mm. in length by 0·4 to 0·45 mm. in breadth. The buccal capsule is much smaller, and presents an irregular border; instead of four ventral hook-like teeth, it has a ventral pair of prominent semilunar plates similar to those of the dog hook-worm, Uncinaria stenocephala; the pair of dorsal teeth is likewise represented by a pair of slightly developed chitinous plates of the same nature. The outlet of the dorsal head-gland, usually called dorsal rib or dorsal tooth, projects prominently in the oral cavity. Deep in the buccal capsule are one pair of dorsal and one pair of ventral subniedian lancets. The caudal bursa of the male presents a short dorso- median lobe, which often appears as if it were divided into two lobes. The dorsal ray is divided to its base, its two branches are prominently divergent, and their tips are bipartite instead of tridigitate, as in A. duodenale. The common base of the dorsal and dorso-lateral rays is very short. In the female the vulva is placed slightly in front of the middle of the body. The eggs (Fig. 168, e) are larger than in ankylostomum; they measure 64 to 75 μ. in length by 36 to 40 μ in breadth.

N. americanus inhabits the small intestine of man, and so far has not been found in any other part.

The life-history of this worm has not yet been fully investigated; it is probably similar to that of A. duodenale.

ANKYLOSTOMUM CEYLANICUM, Looss, 1911

Synonym.—Ankylostomum braziliense, Faria, 1910.

This parasite has been found by Lane in stools of three prisoners in Mymensing jail in India. A. ceylanicum is a parasite of the civet cat in Ceylon, but according to Leiper it is apparently identical with A. braziliense, a common parasite of dogs and cats in Brazil. It has also been found in an African lion born in the Calcutta Zoo. The males are 5 mm., the females 7 mm. long. There are two pairs of ventral marginal teeth. The bursa of the male has clefts dividing the dorsal from the lateral lobes; the dorsal ray bifurcates, each branch bifurcating again. This species is probably of little importance as a parasite of man.

ANKYLOSTOMIASIS

History.— Although Griesinger had previously shown that Egyptian chlorosis was due to the presence of the ankylostomum in the small intestine, and although similar observations had been made on negroes in America, it was not until the very fatal epidemic of anæmia among the miners in the St. Gothard Tunnel (in 1880) had called the attention of European observers to the subject, that the importance of this parasite as a pathogenic agent began to be properly apprehended. Multiplied observations have now shown that, although very minute, these blood-sucking parasites, if present in large numbers and for a length of time, more especially if its victims are poorly fed, are very dangerous ones indeed. The constant drain of blood which their presence entails, the catarrh arising from the irritation caused by the wounds they inflict on the mucous membrane, the consequent impairment of nutrition, and, possibly, the absorption of some hæmolytic toxin— the product of the parasites— give rise to a grave cachexia, disqualifying to a greater or lesser extent the subject of it for work, and, not infrequently, leading to a fatal issue. It is now recognized that many of the cases which were formerly regarded and diagnosed as " tropical anæmia " are cases of ankylostomiasis.

It is not in every instance in which the ankylostomuin is present that consequences so serious ensue. There may be dozens of ankylostomes in the intestine without any appreciable anæmia, or, indeed, symptoms of any description whatsoever. Grave symptoms are the exception. One must be careful, therefore, to avoid concluding that the ankylostomum is the cause of every pathological condition with which it may chance to concur.

On the other hand, many inhabitants of tropical and sub-tropical countries are in a state of chronic starvation. Living on coarse, bulky, and innutritious food, they are prone to dilatation of the stomach and dyspeptic troubles. In such, any additional cause of malnutrition, as a swarm of ankylostomes, and a daily though perhaps small loss of blood, may be sufficient to turn the scale against them. In those countries, as elsewhere, there are many who live just on the border-land between health and disease; to such the ankylostomum may prove the last straw that breaks the camel's back.

It may be that in some individuals with special susceptibility, some toxin developed by the parasite, just as in certain cases of Dibothriocephalus latus infection, produces a special type of anæmia. It is evident that as a complication in typhoid, in kidney disease, in dysentery, in malaria, in fact in any chronic or exhausting disease, the importance of this anæmia-producing parasite cannot be ignored.

The practitioner in the tropics, therefore, must be constantly on the look-out in all cases of anæmia, of dyspepsia, and of debilitated conditions generally, for the ankylostomum. He must bear in mind that this parasite, as will be presently pointed out, if permitted to remain in the intestine for a length of time, may be the cause, not only of remediable anæmia, but of irremediable anæmia-produced degenerations of various organs. On this account, also, its early recognition becomes a matter of the first importance.

Further, ankylostomiasis is an important disease from the standpoint of the employer of native labour. The invaliding and inefficiency which it causes among coolies, not to mention the deaths, are of ten financially a serious matter to the planter and the mine-owner. To them, any wisely directed expense or trouble undertaken for the treating and controlling of this helminthiasis will be abundantly repaid by the increased efficiency of the labourer.

Symptoms.— The essential symptoms of ankylostomiasis are those of a progressive anæmia; an anæmia which is generally associated with dyspeptic trouble, but which, in uncomplicated cases, is not associated with wasting. If the progress of a case be unchecked, serous effusions in different organs and fatty degeneration of the heart ensue, and death may occur from syncope or from intercurrent complication.

One of the earliest symptoms of an extensive ankylostomum invasion is pain or uneasiness in the epigastrium. This is generally increased by pressure, but, for the time, may be relieved by food. The appetite, sometimes defective, is more often ravenous, though its gratification is apt to give rise to dyspeptic trouble of various kinds, to colic, to borborygmus, and perhaps to diarrhœa of imperfectly digested food. Constipation may be present in some instances, irregularity of the bowels in others. The taste may be perverted, some patients exhibiting and persistently gratifying an unnatural craving for such things as earth, mud, lime— what is called pica or geophagy. The stools sometimes, though rarely, have a reddish-brown tinge from admixture of half-digested blood. Sometimes they may contain small flakes of bloodtinged mucus. Pure blood is rarely passed; and an extensive hæmorrhage, unless there be concurrent colitis, is still more rare, although, post mortem, considerable quantities of blood may be found in the small intestine. Fever of an irregular, intermitting, or even of a subcontinued type is common. On the other hand, the temperature may be constantly subnormal. Or these conditions may alternate. After a longer or shorter time, symptoms of profound anæmia gradually disclose themselves. The mucous surfaces and the skin become pallid, the face is puffy, and the feet and ankles are swollen. All the subjective symptoms of a definite anæmia now become more and more apparent; there are lassitude, breathlessness, palpitations, tinnitus, vertigo, dimness of sight, mental apathy and depression, liability to syncope, etc. The circulation is irritable, and hæmic bruits can be heard over the heart and larger blood-vessels. Ophthalmoscopical examination may reveal retinal hæmorrhages.

From some of these symptoms, were it not that with the advancing anæmia there is no loss of weight, one might be led to suspect the possibility of tuberculous or cancerous disease, or of Bright's disease. So far from losing weight, the patient may appear quite plump and, though hæmocytometric estimates testify to a slow and steady fall in the corpuscular richness of the blood until the lowest limit compatible with life is reached, there is no true poikilocytosis as in idiopathic pernicious anæmia, no excessive leucocytosis as in leucocythæmia, and not necessarily any enlargement of lymphatic glands, liver, or spleen. There is generally a marked eosinophilia. The depression in the hæmoglobin value of the corpuscles is considerably greater than the fall in their numbers.

The rate of progress is very different in different cases. In some a high degree of anæmia may be attained, and even a fatal issue ensue within a few weeks or months of the appearance of the first symptoms. Such rapid cases are rare; more frequently the disease is an exceedingly chronic one, ebbing and flowing or slowly progressing through a long series of years.

Should serious ankylostomiasis occur before puberty, the growth and development are apt to be delayed and stunted.

Diagnosis.— Provided its presence be suspected, ankylostomiasis is easily diagnosed. In tropical countries, in patients coming from tropical countries, and in miners who work in very warm mines in cooler climates, anæmia with concurrent eosinophilia should always suggest a microscopical examination of the fæces. If the ova (Fig. 168, b, e, and Fig. 173) of A. duodenale or of N. americanus are discovered,*[2] and no other reason for the anæmia be made out, the presumption is that one of these parasites is at the root of the mischief; at all events, no harm is likely to result from treatment based on this supposition. On the other hand, if no ova are found it must not be concluded that the case is not one of ankylostomiasis; for it sometimes happens that, in the later stages of the disease, symptoms will persist although the parasites which caused them in the first instance have disappeared spontaneously, or have been got rid of by treatment. Permanent degeneration of the alimentary canal, of the heart, liver, kidneys, and blood-forming organs, may remain, and even prove fatal, although the primary cause is no longer present. The history and the absence of other sources of anæmia are all we may have to go upon for diagnosis in such circumstances.

Ankylostomiasis is sometimes confounded with beriberi, and vice versa. The presence of paretic and cardiac symptoms not accounted for by the moderate degree of anæmia in beriberi, and their absence in ankylostomiasis, suffice for diagnosis. The anæmia of ankylostomiasis differs from that of malaria, inasmuch as the latter is accompanied by enlargement of the spleen, a sallow and perhaps pigmented complexion, an icteric tint of the scleræ, occasional attacks of well-marked periodic fever controlled by quinine, and, especially, the presence at such times of the malaria parasite in the blood. As an additional diagnostic feature, Rogers has pointed out that whereas in malaria the loss of hæmoglobin is in proportion to the loss of red blood-corpuscles, in ankylostomiasis it is in excess of this. Of course, ankylostomiasis and malarial cachexia may concur, and often do concur, in the same individual.

Some idea of the intensity of the infection may be got from an enumeration of the eggs in a given quantity of fæces; according to Grassi and Parona, the presence of 150 to 180 eggs per c.cg. indicates an infection of about a thousand worms, male and female.

Pathological anatomy and pathology.— As already mentioned, the bodies of the victims of ankylostomiasis are not wasted; on the contrary, there is plenty of fat in the usual situations. The appearance of plumpness is further increased by a greater or lesser amount of general œdema. There may be effusions in one or more of the serous cavities. All the organs are anæmic. The heart is dilated and flabby, its muscular tissue being in a state of pronounced fatty degeneration. The liver, also, is fatty, and so are the kidneys.

If the post-mortem examination be made within an hour or two of death, the ankylostomes, .in numbers ranging from a few dozens up to many hundreds, will be found still attached by their mouths to the mucous surfaces of the lower part of the duodenum, of the jejunum, and, perhaps, of the upper part of the ileum; but if the examination has been delayed for some hours, the parasites will have dropped their hold, and are then to be found lying in the mucus coating the inner surface of the bowel. Many small extravasations of blood —some fresh, others of long standing— are seen in the mucous membrane, a minute wound in the centre of each extravasation representing the point at which the parasite had been attached. Sometimes blood-filled cavities, as large as filberts, are found in the mucosa; each cavity enclosing one or two worms and, probably, communicating by means of a small hole with the interior of the intestine. Old extravasations are indicated by punctiform pigmentations. There may be evidence, in the shape of vesiculations and thickening of the mucosa, of a greater or lesser degree of catarrh. Occasionally, streaks or large clots of blood are found in the lumen of the bowel.

Daniels and others report that microscopical examination of the liver and kidneys shows the presence, within the cells of the parenchyma, of grains of yellow pigment having the reactions of hæmatoidin; indicating an intravascular blood destruction such as occurs in pernicious anæmia and other diseases in which excessive hæmolysis is a feature. On this account, and also because he finds granules of a ferrous nature in the liver cells, Daniels concludes that the anæmia in ankylostomiasis is, in a measure, the result of blood destruction within the vessels by some toxic substance produced by the parasite and absorbed from the bowel. These results have not been confirmed by all other observers; on the contrary, the late Dr. Beaven Rake concluded, from careful estimates of the amount of iron in the livers of five cases of ankylostomiasis, that in this disease the hepatic iron is below the normal average, and that the anæmia is entirely owing to the direct abstraction of blood by the parasites. Further observations are necessary before this question can be decided.

Treatment. Malefern.— Until the introduction of thymol by Bozzolo in 1880, extract of male fern was the anthelmintic usually employed in ankylostomiasis.

Thymol.— Before the administration of thymol the patient should be put on liquid diet for a day or two, and have the bowels well cleared out by an aperient. In the morning, and following the action of the aperient, three or four 10- to 30-gr. doses of welltriturated thymol, in cachets, in capsules, or in emulsion, are given on an empty stomach at intervals of an hour. If the bowels do not open spontaneously within four or five hours of the last dose an aperient should be given. Usually, by this treatment many ankylostomes are expelled and may be found in the motions. One such course of thymol may suffice; but it is well, after a week has elapsed, again to examine the stools microscopically, and, if it be found that ova are still being passed, to repeat the course of thymol once or oftener.

Certain precautions have to be observed in employing this drug. At times it gives rise to a very unpleasant form of intoxication vertigo, excitement etc., and the urine may become dark, as in carbolicacid poisoning. It is advisable therefore for the patient, while taking the drug, to keep his bed and to lie down for several hours after the last dose. Thymol is very insoluble in water, and is consequently, in ordinary circumstances, not readily absorbed in poisonous quantities; should, however, the patient, while thymol is present in the stomach, partake of any alcoholic drink, there is considerable risk of poisoning ensuing. Alcohol, ether, glycerin, turpentine, chloroform, and oils are all solvents of thymol, and must therefore be avoided when this drug is being exhibited. Thornhill related an instance in which a fatal result was brought about, apparently, by neglect of the obvious precautions suggested by these facts. A man had received 30 gr. of thymol in water at 7 a.m. " He experienced no special symptoms after it, and at 9 a.m. the nurse gave him a second dose of 30 gr. As this man was supplied with arrack as an extra, and as in such cases a portion of the arrack was usually given at 9 a.m., the nurse gave it to him just after administering the second dose of thymol. The result was that intense collapse set in almost at once, and, notwithstanding all efforts, the man died within twenty-four hours, the collapse manifestly being due to the arrack dissolving the thymol, which was thus absorbed." Thornhill mentions two additional fatal cases of thymol poisoning occurring in his experience; other writers have recorded similar fatalities. For this reason, and because it is an extremely unpleasant drug to take— sometimes giving rise to severe burning sensations in the stomach, throat and gullet, and, not infrequently, to excitement, giddiness, fainting, and vomiting— an equally efficient but safer drug is a desideratum.

Without careful preparation by rest and judicious feeding, thymol must on no account be used in advanced cases of ankylostomiasis or where prostration is extreme. It is contraindicated in gastritis, dysentery, nephritis, and in active heart disease.

Oleum chenopodium in three or four successive doses of 15 drops each is reported to be as efficacious as thymol, less unpleasant to take, and more free of risk to the patient.

Beta-naphthol given in the same way, in doses of 15 gr. repeated at intervals of two hours for two or three times, is nearly as efficacious, is cheaper, and much less unpleasant, and is therefore to be preferred to thymol.

Oil of eucalyptus 30 minims, chloroform 45 minims, castor oil 10 drachms, one half first thing in the morning, the other half thirty minutes later, is a very efficient vermifuge in ankylostomiasis, much less unpleasant and much less dangerous than any of the foregoing. It can be repeated for several days in succession. I have used this combination several times in Europeans who had on previous occasions taken thymol; they preferred the eucalyptus mixture. The dose of chloroform is a large one, but, in my experience, it has never had any ill effects. A daily dose of 5 gr. of thymol, kept up for several weeks, has been advocated by some practitioners of experience and might be tried in those cases of ankylostomiasis in which more drastic treatment is contraindicated by a condition of extreme debility.

Convalescence.— The dieting of convalescents from serious ankylostomum disease must, for a time, be very carefully conducted. In such, a rich, full dietary is to be avoided until the powers of digestion have become re-established; otherwise, enteritis and diarrhœa may prove very troublesome and retard recovery —perhaps prevent it altogether. Iron and arsenic are indicated as blood restorers.

Prophylaxis.— In devising a system of prophylaxis for ankylostomiasis, the fact that it is by means of the fæces of the already infected that the parasite is spread must be kept prominently in view. Fæcal contamination of the soil and water must therefore be prevented. The promiscuous deposition of fæces about huts, villages, and fields must be interdicted. Abundant and easily accessible privy accommodation must be provided in coolie lines, in miners' camps, in native villages, and along the highways of traffic. In the absence of a more elaborate system of conservancy, pits or trenches will suffice. They may be filled up with earth and fresh ones opened from time to time. I believe the Chinese plan of storing night-soil for months in large, cemented, watertight pits is a good one. It is known that if the ova of the ankylostomum are kept in pure fæces the embryo is developed and escapes from the egg in due course.; but it is also known that, unless the embryo be supplied with a certain amount of air and earth, it soon dies. The thing to be avoided, therefore, is the mixing of fresh fæces with earth. By the Chinese system the embryos of the ankylostomum are killed, and, at the same time, a valuable fertilizer is secured for the agriculturist.

It is manifest that in devising privies and sanitary regulations the habits of the people they are intended to benefit must be taken into account; if this be not attended to, if native habits and prejudices are ignored, any system, no matter how perfect it may be in theory, will fail in practice. The water supply should also be carefully guarded from all possible sources of fæcal contamination. Drinking-water, unless above suspicion, should be boiled or strained. So far as possible, facilities for removing all earth and mud from the hands and dishes before food is partaken of should also be provided and their use encouraged.

Badly contaminated ground had better be abandoned. If this should be found impracticable, the soil should be turned over with the plough, or roasted with grass fires, or treated in such a manner that any ova or embryos it may contain are destroyed or buried. The systematic periodical inspection of plantation coolies is to be recommended. At these inspections all subjects of anæmia or dyspepsia should be put aside for more careful examination; if the ova of ankylostomes are found in their fæces a judicious dosing with some of the drugs above mentioned may avert serious disease in the individual, and also prevent him from becoming a source of danger to his companions.

In view of the great danger to health that exists in certain countries from this and similar parasites, the sanitary authorities in such places ought to circulate among the people, by means of printed leaflets or posters, a few simple directions for the prevention of ankylostomiasis and kindred diseases.

Recently attempts have been made in Porto Rico and elsewhere to reduce or exterminate the prevailing ankylostomiasis. Special officers have been detailed for the purpose, whose duty it is to submit the entire population to systematic drugging with β-naphthol. The result in the improvement of the general health and increase in the aggregate labour capacity has been most encouraging. This is an example of sanitary energy which we might follow with advantage in our own tropical possessions.*[3]

ANKYLOSTOMUM DERMATITIS

A form of dermatitis affecting the feet of coolies on plantations in Assam, in the West Indies, and probably elsewhere in the tropics, and variously known as ground itch, pani-ghao, water itch, water pox, water sores, sore feet of coolies, has been ascribed by Bentley to the penetration of the skin by anky lostomum larvæ. This disease is of much economic importance to the planter.

The soil in the neighbourhood of coolie lines is extensively contaminated by fæcal matter. During rainy weather the ankylostomum ova in the fæcal materials are hatched, and the larvae escape into, and possibly multiply in, the damp earth. The bare feet of the coolies are constantly soiled with this larva-laden earth, and in this way, in many tropical plantations, Looss's experiment is unintentionally carried out on a large scale. Dermatitis, vesiculation, and it may be pustulation or even extensive ulceration, and probably ankylostomiasis anæmia ensue. The services of the affected coolie are lost to the planter till the irritation or ulceration subsides and the anæmia is cured.

Bentley's suggestion has been contradicted by Dalgetty, Stiles, and others. Looss also points out that the symptoms of ground itch do not tally with those caused by the penetration of ankylostomum larvæ through the skin. Perhaps coolie itch may not in every instance be produced in this way, but undoubtedly it is so in a proportion of cases. A patient of mine, a sugar planter, who at that time knew nothing about the ankylostomum, observed that an attack of coolie itch in any of his labourers was sure to be followed by anæmia. He assumed that the skin trouble was the cause of the anæmia, and that the former was produced by a micro-organism picked up from the soil. He made his coolies, on going out to their work in the morning, walk through a bucket of Barbados tar, and then through a heap of sand, with the result that coolie itch and anæmia ceased on his estate. Personal cleanliness and the use of some form of foot-covering during the wet season, together with the prophylactic measures for ankylostomiasis already mentioned, are the special preventive means indicated as against this disease. As regards treatment, antiseptic foot-baths and some soothing ointment are indicated.

ŒSOPHAGOSTOMUM APIOSTOMUM, Willach, 1891.

Synonym.— Œ. brumpti, Railliet and Henry, 1905.

History.— The occurrence in man of this parasitic nematode was discovered by Brumpt, in 1902, at the post-mortem of a thirty-year-old Pouma negro on the river Omo, Africa. Six immature females were found within cyst-like nodules in the wall of the cæcum and colon. Subsequently the same parasite was found by Leiper in natives from northern Nigeria. Johnson found that 4 per cent, of the prisoners in Zungeru jail were infected with the same helminth. We know already of a number of species of the same genus occurring in the Quadrumana. Œ. apiostomum has been found in the gorilla, in the orang-outang, in the chimpanzee, and in various monkeys belonging to the genera Cercopithecus, Cynocephalus, and Macacus; in these, if the infection is severe, it gives rise to dysenteric symptoms.

The parasite.—The young females found by Brumpt varied in length from 8.5 to 10.2 mm. and presented a maximum breadth of 295 to 325 μ. The cuticle is transversely striated; the anterior extremity exhibits the ovoid cuticular expansion characteristic of the genus, limited anteriorly by a salient oral ring (oral vestibule), and posteriorly by a constriction which is especially marked on the ventral surface and 200 μ. distant from the oral vestibule. The posterior extremity of the female worm tapers gradually to a caudal point slightly bent dorsally. The male has a terminal bursa similar to that of the Ankylostomum duodenale, but differs in that the trunk of the dorsal ray bifurcates, some distance from the bursal edge, into two branches forming a horseshoe-shaped structure, each limb of which gives off a short lateral horn near its base. The oral vestibule is provided with a crown of twelve sharp chitinous plates directed forwards and inwards, and bears six papillæ, two lateral and four submedian. The œsophagus is club-shaped and measures 470- 500 μ in length by 150 μ in its widest diameter. Anteriorly, it opens into the oral capsule with three slightly recurved teeth about 8 μ long, which fit into three corresponding indentures of the posterior border of the oral capsule. Posteriorly, it presents a three-lobed valve. The intestine rims almost in a straight line to the anus, which opens at 170-200 μ, from the posterior extremity. The vulva is placed anteriorly to the anus at 350-475 μ. from the caudal end. Neither anus nor vulva is marked by any prominence of the body wall.

The ova of Œ. apiostomum, like those of other parasites belonging to this genus or to the closely allied genus Sclerostoma, probably hatch in water, and by this medium reach a fresh host, penetrating either through the œsophagus or the skin. They finally settle beneath the intestinal mucosa, usually between the ileo-cæcal valve and the anus, and here grow considerably in size, feeding on the blood of the host. Having practically reached the adult stage, they leave their cysts for the purpose of copulation and oviposition, and they and their eggs are expelled with the fæces.

Life-history and pathogenesis.—The allied species, Œ. columbianum, which, according to Curtice, is frequent in adult sheep in the south of the United States and is more particularly observed in the autumn and winter, does not appear to cause any serious trouble except when present in great numbers. The parasite may be found in its adult state within the lumen of the cæcum or colon, but it is found more frequently in the larval stage lodged beneath the mucous membrane in cysts varying in size from that of a pin's head to that of a hazel-nut, each cyst containing a coiled-up worm. The species peculiar to apes and monkeys are likewise found during their larval stage within small hæmorrhagic cysts beneath the mucosa of the cæcum and large intestine. The parasites are blood-suckers; their intestines are crammed with erythrocytes. The larger cysts usually present a small perforation at their summit; through this the worm protrudes and escapes. Œ. dentatum, which inhabits the pig, the wild boar, and the white-lipped peccary (Dicotyles labiatus), is found not only in the cæcum and colon, but also farther up in the small intestine, and von Lin stow found it within the liver. According to Railliet, the eggs of this species hatch in water within three or four days, the liberated embryo measuring 200-250 μ.

TRIODONTOPHORUS DEMINUTUS, Railliet and Henry,

1905

This sclerostome (Fig. 184) is an intestinal parasite of monkeys inhabiting the large intestine. It has several times been found in natives, post mortem, by Turner in the Transvaal and by Stannus in Nyasaland. The worms are about the size and shape of a female ankylostome. The male is 9.5 mm. long and 0.56 mm. broad; the female, with a tapering pos- terior extremity, 14-16 mm. in length and 0.73 mm. broad. The male has a terminal bursa provided with a posterior ray split into two widely arching component parts, vaguely recalling the arrangement in œsophagostomum. The genital orifice of the female opens posteriorly. The vagina is short and opens into two uterine tubes. The mouth collar is moderately developed, and the entrance to the mouth is surrounded by a double series of delicate fringes composed of cuticle—the corona radiata. The buccal capsule is a barrel-shaped chitinous

Fig. 184.—Triodontophorus deminutus, female. (After Leiper.)

1, Anterior extremity; 2, posterior extremity. C.R., corona radiata; B.C., buccal cavity; Ch.P., chitinous plates; N., nerve ring; Œs., œsophagus; Ch.I., chyle intest.; Ut., uterus; Vag., vagina; V., vaginal opening; R., rectum; A., anus.

structure; posteriorly it comes into contact with the œsophagus. The œsophagus is stout and muscular and triradiate on section. Each of the surfaces of the œsophagus terminates in a chitinous plate projecting into the buccal capsule. The cuticle is transversely striated.

PHYSALOPTERA MORDENS., Leiper, 1907

This appears to be a common human intestinal parasite in Central Africa. Leiper found it frequently in material sent by Dr. Turner from natives of Portuguese E. Africa. From its resemblance to Ascaris lumbricoides it has been taken for miniature specimens of that species. The males are 50 mm., the females 55 mm. in length, and 2-3 mm. in breadth. The posterior end tapers rapidly in the female, terminating in a sharp point. The mouth has a cuticular cuff and two lips provided with papillæ and teeth. The bursa is bladder-shaped with pedunculated external papillae and unequal spicules. The female has two ovaries and vulva situated anteriorly.

SYNGAMUS KINGI, Leiper, 1913

Dr. King, of St. Lucia, forwarded some specimens of this parasite in copula to Leiper; they are said to have been coughed up by a woman.

Copulation is permanent, males and females being found adherent to one another. The male has two equal spicules and the caudal bursa is provided with many ribs; the mouth is large and terminal, leading into a dilated buccal capsule, at the bottom of which there are six sharp teeth.

Leiper was first of opinion that the parasite was near to S. trachealis of poultry, and an accidental occurrence in man. Further examination has convinced him that it is probably a new species more nearly related to the members of the genus found in mammals, but more especially to S. dispar of the puma (Felis concolor).

STRONGYLOIDES STERCORALIS (Bavay, 1876)

Synonyms.—Anguillula stercoralis; A. intestinalis; Leptodera stercoralis; L. intestinalis; Rhabdonemaintestinale.

It sometimes happens that, while searching the fæces for the ova of the ankylostomum, the observer is astonished by seeing a small, snake-like animal (Fig. 185) suddenly rush across the field of the microscope. On careful examination, this animal is found to be about 0.2 mm. or 0.3 mm. in length by 0.013 mm. in breadth; to have a sharply pointed tail and a rounded head; to be transparent; and to exhibit a short œsophagus which terminates in a double œsophageal bulb, the posterior end of which is provided with three tooth-like segments. This is the larval form of Strongyloides stercoralis.

Strongyloides stercoralis was discovered by Normand in 1876. For a time it was supposed to be a cause of a form of chronic diarrhœa very prevalent in Cochin China. Later investigations, while clearing up the natural history of the parasite, have robbed it of any claim to pathological importance. It has been found that, though not so common, its geographical distribution is about coextensive with that of Ankylostomum duodenale, and that the physical conditions demanded for the non-parasitic stages of these two worms are about the same. Powell found it in India in about 15 out of every 20 cases of anæmia. The mature strongyloides (Fig. 186) is a minute, slender worm, measuring 2-3 mm. in length by 0·06 mm. in breadth. No male parasite has been discovered. The adult female i eadily recognized by her dimensions, and by the string of five or six ellipsoidal eggs (0·01 mm. by 0·034 mm.) visible about the centre of the body.

As Kanazy has shown, the parasite bores deeply into the mucous membrane of the intestine, and frequently into the epithelium of Lieberkühn's glands, both for nourishment and oviposition. The eggs develop in the intestinal wall, so that

Fig. 185.—Strongyloides stercoralis. (Partly after Looss.)

a. Young larva from fæces; b, mature larva; c, head.

before leaving the host, unless during violent purgation, the larva has escaped and is swimming about in the fæces, as already described, with great vigour, especially when these are fluid. Only in the event of violent purging do the ova appear in the stools. Such ova (Fig. 168, d) are readily recognized by the way in which they are strung together, end to end, inside a delicate tube. On leaving the host, unless they have access to some non-putrefying fluid, the larvæ soon die; it is necessary, therefore, if we would follow their further development, to mix the fæces with water. If this mixture be kept at a low temperature the young rhabditiform larva develops into a filariform larva which, on reaching its host, assumes the mature parasitic form already alluded to. If, on the contrary, the cultivating medium be kept at a higher temperature, the larvæ develop into male (0·7 mm.) and female (1·O mm.) rhabditic forms which, in time, produce in their turn filariform larvæ, similar to those obtained directly from the embryo in cold climates, and capable, on being swallowed by man, of developing into mature Strongyloides stercoralis.

This parasite must undoubtedly produce considerable irritation of the bowel, but its pathogenic role has not been definitely ascertained. It is usually present in large numbers, and has been found occasionally coiled up in the intestinal follicles.

Fig. 186.—Strongyloides stercoralis, female. (After Looss.)

The larvæ may pierce into the lacteals, and have been found in the blood. Van Durme has shown that, like the larvæ of Ankylostomum duodenale, the filariform larvæ of strongyloides may penetrate through the skin.[4] Hitherto the use of anthelmintics has not proved effectual in procuring their expulsion. Sonsino recommends the prolonged exhibition of liquor ferri perchloridi in combination with small doses of thymol.

The prophylaxis for strongyloides is the same as that recommended for Ankylostomum duodenale.

TRICHOSTRONGYLUS SUBTILIS (LOOSS, 1895)

Synonym.—Trichostrongylus instabilis (Railliet, 1893).

Looss has described a very delicate nematode (Figs. 187-9) frequently encountered in Egyptian fellahs, and since found by

Fig. 187.—Trichostrongylus subtilis, male.

Ijima in Japan. Its habitat is the upper part of the small intestine. The male, which is provided with two spicules, is

Fig. 188.—T. subtilis, female.

Fig. 189.—T. subtilis, bursa.

(After Looss.)

from 4 to 5 mm. in length by 0·07 mm. in breadth; the female is slightly larger and is much more abundant than the male. The eggs (Fig. 168, a) are oval, thin-shelled, with an unsegmented vitellus, and measure 63 μ by 41 μ. This parasite does not occur in large numbers; and, as its mouth is unarmed and its dimensions are exceedingly minute, it does not appear calculated to give rise to any particular symptoms.

GNATHOSTOMUM SPINIGERUM (Owen, 1838)

Synonyms.—Cheiracanthus siamensis; Strongylus siamense (Levinsen, 1839).

History.—Gnathostomum spinigerum was discovered by Deuntzer in Bangkok (Siam), and described by Levinsen, who proposed to call it Cheiracanthus siamensis.

Geographical distribution.—So far it has been seen in Siam only. It was met with in three patients, one of whom had five or six of these worms.

Fig. 190.—Gnathostomum spinigerum.

(After Levinsen.)

The parasite.—Only one female specimen was preserved and forwarded to Levinsen (Fig. 190). It measured 9 mm. in length by 1 mm. in breadth. The cephalic extremity, slightly narrower than the rest of the body, had the appearance of a rostellum surmounted by two lips and was surrounded by eight rows of hooklets. The posterior extremity terminated in a three-lobed prominence, at the base of which the anus opened. The anterior third of the body was beset with tridentate spines, followed by scattered simple spines, which gradually became smaller and then disappeared entirely. The vulva opened a little behind the middle of the body. Subsequently, Leiper described the male—it measured 10·5 mm. by 0·6 mm. It had two large fleshy lips; two unequal spicules; two preanal and two postanal papillæ. Leiper considers its normal host in Siam to be the cat.

Life-history and pathogenesis.—We know nothing of the life-history of Gnathostomum spinigerum. Other species of the genus live in the stomach of various vertebrates. Before attaining maturity they are found in cysts beneath the mucosa. G. spinigerum is found in various kinds of wild cats (Felis catus, F. concolor, F. tigris). Lewis found it in the pariah dogs of Calcutta. G. hispidum lives in the stomach of hogs. Fedschenko found it in a Turkestan wild hog and in a Hungarian domestic hog. Csokor found it in hogs slaughtered at Vienna, Strose in Bakony's hogs, and Collin in cattle in Germany. In Vienna butchers have long known this parasite under the name of "three-coloured worm." The parasite described by Levinsen came from a young Siamese woman, who presented a livid and painful tumefaction of the breast with slight fever. Rounded nodules the size of beans appeared at the seat of inflammation, beneath the skin. From one of these nodules the gnathostomum protruded.

2. TREMATODES

WATSONIUS WATSONI (Conyngham, 1904)

Synonyms.—Amphistomum watsoni; Cladorchis watsoni; Paramphistomum watsoni.

Fig. 191.—Watsonius watsoni.

(After Shipley.)

A, Magnified; B, natural size.

History.—This parasite was found in 1904 by Watson in the duodenum and upper part of the jejunum of a negro patient from German West Africa who died of starvation and diarrhœa. The stools were numerous, watery, and of a bilious colour, and contained many yellow, translucent, oval trematodes. At the post-mortem the jejunum was found to be full of these trematodes, some of them alive and still adherent. The mucosa showed no hæmorrhages, but appeared to be slightly congested. The other parts of the bowel, as also the other organs, were normal. The parasite is said to occur in monkeys and to be common in natives near Lake Tchad.

The parasite.—W. watsoni (Fig. 191) is of a reddish-brown colour and measures 8 to 10 mm. in length by 4 to 5 mm. in breadth; it is oval in shape. The oral sucker is small; the ventral sucker or acetabulum large and at the posterior extremity of the body. The genital pore opens at the anterior end of the ventral surface on a level with the bifurcation of the intestine. The ova measure 125 μ in length by 75 μ in breadth.

Life-history.—We know nothing of the life-history of this parasite, but probably it is similar to that of P. cervi, the conical fluke of cattle and sheep, which was thoroughly worked out by Looss in 1896. The eggs of P. cervi contain a ciliated embryo (miracidium) which escapes from the eggshell under the stimulus of light and moisture. Swimming about in the water, which it must necessarily reach for further development, it penetrates into the visceral cavity of certain snails (Physa alexandrina, P. micropleura), and in these develops and multiplies parthenogenically. In about two months, having attained the cercaria stage, the cercariæ escape from the snail, swim around in the water, and finally encyst themselves on plants or other objects. The final host (cattle, etc.) is attained either through drinking-water or pasture.

Geographical distribution.—Information is as yet very scanty, but there is reason to believe that W. watsoni is by no means uncommon in certain parts of northern Nigeria, where it gives rise to serious intestinal trouble, especially in children. A patient who had lived there for some time told me that on one occasion, being seized with violent diarrhœa, he passed about a pint of material containing innumerable moving bodies which he described as resembling the heads of tadpoles, doubtless specimens of W. watsoni.

Treatment.—As for adult tapeworms.

GASTRODISCOIDES HOMINIS (Lewis and McConnell, 1876)

Synonyms.—Amphistomum hominis; Gastrodiscus hominis (Lewis and McConnell, 1876).

Fig. 192.—Gastrodiscoides hominis.

(Nat size.)

History.—This parasite was described by Lewis and McConnell in 1876 from two sets of specimens, the first procured from O'Brien and Curran, who found them in the vicinity of the ileo-colic valve at the post-mortem of an Assamese in Gowhatty; the second belonging to the Pathological Museum of the Calcutta Medical College, and presented in 1857 by Simpson, who found them in the cæcum and ascending colon of an Indian who died from cholera in the Tirhoot jail hospital. G. hominis is now found to be a much more common parasite of man than was formerly supposed. A study of serial sections has convinced Leiper of the necessity of removing it from the genus Gastrodiscus on the following grounds: (1) the presence of a large imminent genital papilla in place of the genital atrium of gastrodiscus; (2) testes tandem; (3) genital orifice on the neck, not on the ventral surface; (4) ventral aspect of the disc smooth and quite free from sucker-bearing papillæ.

Geographical distribution.— We know little of the geographical distribution of G. hominis; it is probably widely distributed throughout Asia, and appears to be rather common in India. Law and Wise found it in East Indian immigrants in British Guiana; Mackie in seven patients in Assam, by one of whom two hundred worms were passed after treatment with thymol. The pig, apparently, is its normal host (Mathis and Leger).

The parasite (Fig. 192) is of a reddish colour in fresh specimens, and measures 5 to 8 mm. in length by 3 to 4 mm. in breadth. Its body is divided into an anterior rather slender conical portion, and a posterior flattened ventrally concave disc; the oral sucker is small, ventral; the acetabulurn is at the posterior border of the ventral disc. The genital pore opens at about the middle of the anterior portion on a level with the bifurcation of the intestine. The testicles are two in number and lobate; the vas deferens is very sinuous. The eggs are oval, measure 150 μ. by 72 μ, and are operculated. The life-history is probably as in Paramphislomum cervi.

Pathogenesis.— G. hominis is found in the cæcum and colon. The mucous membrane is marked with numerous red spots resembling leech bites. These spots are caused by the parasites, which, attaching themselves to the mucosa by means of their suckers, produce minute pimple-like elevations of the surface. When the parasites occur in great numbers they cause much irritation.

Treatment.— The same as for adult tapeworms and ankylostomes— thymol.

FASCIOLOPSIS BUSKI (Lankester, 1857)

Synonyms.—Distoma buski; Dicrocalium buski; D. rathouisi.

History.—Fasciolopsis buski was first described by Busk in his " Diseases of the Liver," published in London in 1845. Busk found this parasite in 1843 in the duodenum of a Lascar who died at the Sea-men's Hospital. The pig is the normal host.

Geographical distribution.—F.buski is an Asiatic trematode; it has been found in India, Assam, the Straits Settlements, Sumatra, and China. The parasite(Fig. 193) is the largest trematode inhabiting man. It measures 24 to 40 mm. or more (75 mm. according to Busk) in length by 12 to 14 mm. in breadth. In shape it is an elongated oval, rather narrower anteriorly than posteriorly, with flat ventral surface, slightly convex dorsal surface, and very thin margins. It has a smooth skin without spines. The oral sucker (0·5 mm. in diameter) is subterminal and placed on the ventral surface. The ventral sucker is larger (1·6 to 2 mm. in diameter) and placed close to the oral. It is

Fig. 193.—Fasciolopsis buski

(After Odhner.)

prolonged into a kind of sac (2-8 mm. long) directly under the ventral surface. The pharynx (0·7 mm. long) is preceded by a prepharynx (0·28 mm. long); the œsophagus is very short and the intestinal cæca are simple and present two characteristic curves towards the middle line, one at about the middle of the body, the other between the testes. The genital pore opens on the median line immediately anterior to the ventral sucker. The testes are in the posterior half of the body, one behind the other; both are branched dichotomously. The ovary is branched, and is placed about the middle of the body on the right of the median line. The vitellaria are well developed, and extend from the ventral sucker to the caudal end of the body, where they meet. The acini are very small. The eggs (Figs. 169, g, and 194) are numerous and measure 120 to 130 μ in length by 77 to 80 μ in breadth; they are closed, I find, by a very delicate operculum.

Pathogenesis and treatment.—This parasite inhabits the upper part of the small intestine. In two recorded instances (Cobbold) it was associated with attacks of recurring diarrhœa and other signs of intestinal irritation. The best treatment is thymol or eucalyptus oil, given as in ankylostomiasis.

FASCIOLOPSIS RATHOUISI (Poirier, 1887)

Under the name of F. rathouisi a fluke was described by Poirier in 1887. The validity of this species has given rise to a good deal of discussion. Odhner, who has examined the type specimen, believes the so-called distinctive features are solely due to error in the interpretation of serial sections of F. buski.

DICROCÆLIUM LANCEATUM (Stiles and Hassall, 1896)

Synonym.—Fasciola lanceolata.

History.—D. lanceatum was found by Buchholz in the gall-bladder of man in Germany, and has since been noted in Egypt and Italy. It is found commonly in bile-ducts of animals, especially herbivora, in Europe, Africa, and America.

The parasite.—D. lanceatum is a small fluke 8-10 mm. in length by 1·5-2·51 mm. in breadth. It is attenuated anteriorly, and the widest point is just posterior to the yolk-glands. The intestine bifurcates just in front of the genital pore. The testes lie behind the ventral sucker. The ovary

Fig. 194.—Ovum of Fasciolopsis buski, x 250. (Photograph by Dr. J. Bell.)

lies behind the posterior testis; there are a receptaculum seminis and a Laurer's canal. The yolk glands lie in the lateral portion of the middle fifth of the body. The eggs are thick-shelled, yellowish-brown in colour, and measure 38-45 μ by 22-30 μ. Nothing is known of the life-history of the parasite.

HETEROPHYES HETEROPHYES (Bilh. v. Sieb., 1852)

Synonyms.—Distomum heterophyes; Dicrocælium heterophyes; Distoma heterophyes; Heterophyes ægyptiaca; Mesogonimus heterophyes; Cœnogonimus heterophyes; Cotylogonimus heterophyes.

History.—Heterophyes heterophyes was discovered in 1851, in Cairo, by Bilharz at the post-mortem of a child.

Geographical distribution.—It has been reported from Egypt, China, and Japan, and probably has a wide distribution.

Zoological distribution.—Looss has found it in Egypt in the dog (Canis familiaris), in the cat (Felis domestica), in a fox (Canis niloticus?), and in a kite (Milvus parasiticus). Janson reports it from the intestine of the dog in Japan, and Yokagawa in Formosa.

Fig. 195.—Heterophyes heterophyes.

A, Greatly magnified; B, natural size.

The parasite.—H. heterophyes (Fig. 195) is the smallest trematode inhabiting man, excepting Yokagawa yokagawa. It measures 1 to 1.7 mm. in length by 0·3 to 0·7 mm. in breadth. It has an oval, elongate shape and a reddish colour. The neck is not sharply defined from the body, and may be greatly outstretched. The oral sucker (0·09 mm. in diameter) is subterminal and about one-third the size of the ventral sucker (0·23 mm.), which is placed at about the middle of the body. The cuticle is thickly beset with quadrate scales, 5 to 6 μ long by 4 μ broad. The prepharynx is short (80 μ in length); the pharynx measures 50 to 70 μ, in length by 40 to 50 μ in diameter. The œsophagus is about three times as long. The intestinal cæca extend to the posterior extremity, where they converge and terminate close to the excretory bladder. The lateral ends of the vitellaria extend beyond the intestinal cæca. The genital pore opens postero-laterally to, and in the immediate vicinity of, the ventral sucker; it is surrounded by a muscular ring. Testicles oval, in extreme posterior end of body. Ovary globular, median and anterior to the testes. Receptaculum seminis as large as the ovary; uterine coils not numerous, and extending between the ventral suckers and the testicles. Eggs light brown, thick-shelled, oval, 20 to 30 μ by 15 to 17 μ; contain a ciliated embryo when oviposited. (Fig. 169, c.) The life-history of the parasite is not determined. It seems to have little pathological importance. It inhabits the small intestine.

YOKAGAWA YOKAGAWA (Katsurada, 1912)

Synonyms.—Tocotrema yokagawa, Heterophyes yokagawa; Metagonimus yokagawai (Katsurada). This parasite has been found by Yokaguwa to be widely spread among natives of Korea, Formosa, and Japan, in the intestinal tract. It is believed hitherto to have escaped notice from the resemblance of the egg to that of Clonorchis, and the very small size of the adult. According to Leiper the parasite is common in China, in dogs, and belongs to a new genus, Yokagawa, characterized by absence of ventral sucker and the arrangement of the yolk-glands. He maintains that the genital sucker is highly developed but does not possess the circlet of hooks or " antlers " characteristic of the genus Heterophyes, which in other respects it resembles. This interpretation is opposed to that of Yokagawa, who has observed the specimens in a live state and finds that this large disc represents a displaced ventral sucker, and further, as a result of minute study, on developmental as well as morphological evidence, finds that the genital aperture is situated as a minute slit in the anterior aspect of this ventral sucker. The cercarial stage is passed in fresh-water fish, " ayu " (Pkcoglossus altivelis), of. in length by 0.126ten eaten in the raw state by Japanese. Yokagawa has made an elaborate study of the final developmental phase. The cercariæ have a thin and hyaline appearance, and measure 0.14-0.16 mm-0.1 mm. in breadth. They are found attached to the gills, fins, and tails of the fish, much less commonly in the muscles, indicating that the alimentary route is not the usual mode of infection of the fish. Mice and dogs can be infected with the cercariæ. Yokagawa has shown that the cercariÆ can withstand the action of the gastric juice, but that the hyaline capsule is dissolved by its action. The larva) thus set free develop in the duodenum; they are said to be richly studded with pigment granules. Development is very rapid, and the adult stage is reached in seven to ten days after infection. Y. yokagawa is only 1.1 mm. long by 0.42-0.7 mm. broad, and is covered with small spines; in the general disposition of its organs it resembles Heterophyes (Fig. 195); it is easily the smallest fluke found in man. The egg resembles that of C. sinensis in size, but is regularly elliptical in shape, dark brown in colour, and the shell membrane has a double contour, and measures 0.028 mm. in length by 0.016 mm. in breadth. Y. yokagawa is apparently an innocuous parasite in man, causing at most a catarrhal condition of the intestine canal which it inhabits.

Thymol and naphthol are efficient anthelmintics.

ECHINOSTOMUM ILOCANUM (Garrison, 1908)

Synonym.—Fascioletta ilocana.

This parasite was discovered in 1907 by Garrison, who noticed peculiar eggs in the fæces of Philippine prisoners in the prison at Biliprid, in Manila, and subsequently obtained a small number of trematodes from the intestinal canal. Odhner has recently demonstrated a crown cf spines round the oral sucker, and therefore has transferred it to the genus Echinostomum. In length it is 4-6 mm. by 0·75-1·35 mm. in breadth. It is attenuated posteriorly. The acetabulum is much larger than the oral sucker. The genital pore opens separately a little behind the half-way point between the pharynx and the acetabulum. Each testis has an anterior and a posterior lobe. The ovary is globular.

Nothing is known about the life-history of the parasite, beyond the fact that a miracidium hatches in about ten days after the eggs have left the host.

ECHINOSTOMUM MALAYANUM (Leiper, 1912)

Fig. 196.—Tænia saginata.

(After Braun.)

a, Cephalic end magnified;

b, mature segment (nat. size).

This parasite is found in the intestines of natives in the Malay States, but probably is not normally parasitic in man. The body is 12 mm. long by 3 mm. in greatest breadth, and 1·3 mm. in thickness. Both ends of the body are rounded. There is a row of 43 stout spines round the circumoral disc; they vary in size; those on the ventral are 0·07 mm. and those on the dorsal surface 0·05 to 0·16 mm. in length. The oral sucker comprises one-third of the total diameter of the circumoral disc; it communicates with the spheroidal muscular pharynx by a thin-walled portion 0·175 mm. long. The œsophagus measures 0·04 mm. in length, and bifurcates near the pharynx. The main gut branches are simple and end blindly at the hind end of the body. The ventral sucker, 0·9 by 0·75 mm., is several times larger than the oral. The testes are tandem and are deeply lobed; they are situated in the middle of the body behind the ventral sucker. The cirrus pouch is well developed, and extends behind the level of the fundus. The ovary has a smooth surface, and lies immediately in front of the anterior testis, 0·85 mm. behind the ventral sucker.

3. CESTODES

The ordinary tapeworms, Tænia saginata (Fig. 196) and Tænia solium, and their cystic forms, are common enough in the tropics and sub-tropics, their distribution being regulated by the presence or absence of their proper intermediary hosts—the ox in the one case, the pig in the other—and by the habits of the people as regards cooking and conservancy. Echinococcus granulosus (= Tænia echinococcus) of the dog, and its cystic form—hydatids—are found wherever the dog and the sheep are found, that is practically everywhere. The broad tapeworm (Dibothriocephalus latus) is known to occur in Turkestan, in Japan (where the natives are in the habit of eating raw fish), in Madagascar, and among the natives on the shores of Lake 'Ngami, South Africa. Ichthyophagous habits are probably responsible for the occurrence of Diplogonoporus grandis, another

Fig. 197.—Tænia africana.

(After Linstow.      )

Fig. 198.—Tænia africana.

A, Frontal section of mature segment;

B, „ „ gravid „

large dibothriocephalid found by Ijima and Kurimoto in a Japanese from the province of Higen.

The only cestodes of man which, so far as is known, have any claim to be regarded as more or less special to warm climates are T. africana, T. hominis, T. philippina, Hymenolepis nana, Davainea madagascariensis, D. asiatica, Sparganum mansoni, and S. proliferum. Doubtless there are other species which, so far, have escaped observation.

TÆNIA AFRICANA (Linstow, 1900)

History.—Tænia africana was described by Linstow in 1900. It was found in German East Africa, in native soldiers stationed at Langenburg, near Lake Nyassa.

The parasite (Figs. 197-8).—T. africana differs considerably from the common unarmed tapeworm of man. Its strobila attains 1·4 metres in length, and is composed of about 600 proglottides. The scolex is quadrilateral, unarmed, very small (1·38 mm. broad by 0·47 mm. long), and is provided with an apical sucker (0·16 mm.) in addition to the usual four suckers (0·63 mm.). The neck is very short, and somewhat broader than the scolex. The proglottides are all broader than they are long. Immediately at the back of the scolex they measure 0·16 mm. in length by 1·78 mm. in breadth and 0·59 mm. in thickness; about the middle of the strobila they are 3 mm. long by 9 mm. broad and 1·20 mm. thick. The terminal and gravid strobilæ are 7 mm. long by 12 to 15 mm. broad and 1·35 mm. thick. The genital pores alternate irregularly, and are placed in the middle of the border of each segment. The testicles are very numerous and scattered throughout the middle layer. The vas deferens is much convoluted. The cirrus pouch is pyriform and thick-walled. The cirrus and vagina are beset with bristles directed outwards. The receptaculum seminis is fusiform. The ovary consists of two fan-shaped wings, composed of club-shaped tubes centring towards the shell-gland; the latter is median and globular. The uterus includes a median stem and 15 to 24 lateral, unramified branches, which are longer than the stem, and spread out like a fan. The ova are spherical, the embryophore 31 to 39 by 33·8 μ, with thick radially-striated shell; hooks of the onchosphere measure 7·8 μ in length.

Fig. 199.—Tænia hominis, head.

(After Linstow.)

The cystic stage of this tapeworm is unknown. Linstow suggests that it may be found in the zebu (Bos indicus), the flesh of which the natives are in the habit of eating raw.

TÆNIA HOMINIS (Linstow, 1902)

History.—T. hominis was described by Linstow in 1902, from a specimen obtained from the intestine of man in Aschabad, Asiatic Russia.

The parasite (Fig. 199).—The strobila examined by Linstow was immature; it measured 70 mm. in length. The scolex measured 1·34 mm. in length by 2 mm. in breadth, and exhibited a rudimentary unarmed rostellum. At the back of the suckers there was a characteristic circular ridge. The genital organs were not developed.

The cystic form is unknown.

TÆNIA PHILIPPINA (Garrison, 1907)

This parasite was found by Hare in the prison at Biliprid, Manila. It is 80-100 cm. in length. The head is cube-shaped with unarmed retractile rostellum and four suckers. The neck is segmented. The proglottides number about 800; the mature proglottides are 4-5 mm. in width by 0·8-1 mm. in length. The surface and margins extend posteriorly in an elongated cuff-like projection over the succeeding segment. The testes are 130-160 μ in length and 60-80 μ in breadth; the vas deferens is without a vesicula seminalis. The cirrus pouch is absent. The genital pore is situated irregularly on the lateral borders. The vagina is coiled and without setæ. The mature uterus is very compact with a median stem and numerous long, slender dichotomous branches.

HYMENOLEPIS NANA (v. Siebold, 1852)

Synonyms.—Tœnia nana; Diplacanthus nanus; Hymenolepis murina.

History.— This minutest of the tapeworms inhabiting man was first found as a human parasite by Bilharz, in Cairo, in 1851. The following year it was described by von Siebold, who proposed to call it Tœnia nana. In 1887 Grassi identified it with Hymenolepis murina of the rat, and showed that it can dispense with an intermediary host, the larva penetrating into a villus of the rodent's intestine to become a cysticercoid, and then re-entering the canal to become transformed into the adult stage.

Zoological distribution.—H. nana is found in the brown rat (Mus decumanus), black rat (M. rattus), house mouse (M. musculus), dwarf field-mouse (M. minutus), and garden dormouse (Eliomys guercinus).

Geographical distribution.—H. nana is found in Egypt, Siam, Japan, the southern States of the American Union, Brazil, Argentine, and through-out Europe, but more especially in the warmer parts, as in Sicily, where, according to Calandruccio, 10 per cent, of the children are affected.

The parasite(Fig. 201).— The strobile vary in length from 5 to 45 mm. with the number of proglottides, which may be from about 100 to 200. The scolex is subglobular and measures 139 to 480 μ. in diameter; it is provided with a well-developed rostellum armed with a single crown of twenty to thirty booklets 14 to 18 μ. long; the suckers are globular and have a diameter of 80 to 150 μ. The neck is long. The proglottides are very short anteriorly; farther down the chain they increase in size but remain broader than long. Only the hindermost segments may equal or even slightly exceed their breadth. The maximum breadth of the proglottides is from 0.5 to 0.9 mm. The genital pores open on the left margin near the anterior border of each segment. There are three testes in each segment; the vas deferens widens to form a seminal vesicle within the cirrus pouch. The gravid uterus occupies nearly the entire segment. The eggs number from 80 to 180 in each proglottis; they are oval or globular, and present two distinct membranes; the outer one measures from 30 to 60 μ in diameter, the inner one from 16 to 34 μ. The latter exhibits at each pole a more or less conspicuous mammillate projection.

Development.—The development of Hymenolepis nana has been worked out experimentally by Grassi in the rat. The egg is swallowed, and after hatching enters a villus in the lower part of the small intestine (Fig. 200), where it transforms into a cercocystis.[5] The six-hooked embryo is found concysted from 24 to 50 hours after ingestion, its long axis corresponding to that of the villus, and the posterior end bearing the embryonal hooks directed towards the lumen of the intestine. Occasionally two parasites may be found in the same villus. In about 40 to 70 hours after ingestion the scolex has appeared, and in 80 to 90 hours after ingestion the rostellum is

Fig. 200.—Embryo of Hymenolepis nana

in small intestine.

Fig. 201.—Hymenolepis nana

(magnified).

provided with booklets. Then the parasite passes into the lumen of the intestine, where it can be seen attached to the epithelium of the villus with short neck and no trace of segmentation. The rapidity of development varies somewhat, and, as a rule, various stages are found occurring simultaneously in the same host. Strobilization is rapid; the proglottides attain maturity in about 10 or 12 days, and about 30 days after infection the eggs of the parasite begin to appear in the fæces. These never develop in the same host unless reintroduced per os or through a reverse peristalsis, because, as in Oxyuris vermicularis, the embryo will not hatch unless the egg be subjected to the action of the gastric juices. Young white rats proved most susceptible to the infection, whilst rats already harbouring the parasites were refractory. Grassi's observations do not entirely disprove the possible agency of an intermediary host as in other tapeworms, but they certainly show that it can be dispensed with, and indeed that as a rule the rat acts both as definitive and intermediary host. Experiments in man were not conclusive. Out of eight persons fed with eggs or mature segments of the parasite both from man and rats, only one became infected. This occurred, however, in a region (Catania) where many harbour this tapeworm.

Pathogenesis.—H. nana is very minute, but as a rule it occurs in large numbers— usually hundreds, not infrequently thousands. When attached to the intestine it fixes its rostellum deeply into the lumen of a Lieberkiihn's follicle, thus altering and destroying many of the epithelial cells. It is obvious, therefore, that a number of these worms must give rise to considerable irritation and possibly favour secondary infection. According to Grassi, H. nana may bore deeply into the mucosa; and at the post-mortem of a case in which 400 specimens were found in the ileum, Visconti and Segré noticed that the mucosa throughout the small intestine was tumefied, hypersemic, and covered with a thick layer of greyish mucus, through which the worms were scattered. The most frequent symptoms reported by authors are abdominal pain, which may or may not be associated with diarrhœa; convulsions of various sorts,frequently epileptiform; headache and strabismus. The nervous phenomena are ascribed to the absorption of toxic products elaborated by the parasite. On account of its small size this parasite is easily overlooked. Diagnosis is based 011 the presence of the characteristic ova in the fæces. Some care is requisite in looking for the eggs, because, owing to their transparency, they may escape observation.

Treatment.—H. nana is readily expelled by male fern. If a patient harbours this parasite he should not be allowed to sleep in the same bed with another person. On prophylactic grounds, rats and mice should be banished from the house, and all food kept out of their reach.

DAVAINEA MADAGASCARIENSIS (Davaine, 1869)

Synonyms.—Tænia madagascariensis; T. demerariensis.

History.—Davainea madagascariensis was first described by Davaine in 1869 from fragments of two strobilæ without heads sent to him by Grenet, who discovered it at Mayotte, Comoro Islands, in two Creole children. In 1891 Leuckart described an entire specimen with scolex which was sent to him from Siam. But it is chiefly to Blanchard that we owe our knowledge of this parasite.

Fig. 202.—Davaine

madagascariensis.

(After Blanchard.)

A, Head (magnified);

B, parasite (nat. size).

Geographical distribution.—The first two cases published were those of Grenet at Mayotte, but both came from abroad. One of them was an eighteen-months-old child who had arrived from the Antilles five months previously, the other a little two-year-old girl from Réunion who had landed two months previously. The next four cases were seen at Port Louis (Mauritius) by Chevreau, who looked for the parasite at Blanchard's suggestion. All these cases occurred in children, two of whom were only 5 years old. The seventh case, published by Leuckart, occurred at Bangkok (Siam) in a three-year-old boy, the son of a Danish sea-captain. The eighth was that of Daniels, who discovered the worm in an adult native at Georgetown (British Guiana). A further specimen was described by Blanchard, who found it in Davaine's collection with the following label: "Nossi-Bé (Island), November, 1873; passed by a little girl 3 years old." More recently, Garrison has described two cases in the Philippines.

Zoological distribution.—As yet D. madagascariensis has only been found in man, but the genus is widely distributed in mammals and birds. Amongst mammals it is found in rats (Mus siporanus, Mus rajah), in hares (Lepus sylvaticus, L. arizonæ, L. melanotis), in the pangolin (Manis pentadactyla). Amongst birds it is found in the ostrich (Struthio camelus), the common rhea (Rhea americana), the emu (Dromæus novæ hollandiæ), the little egret (Ardea garetta), the grey parrot (Psittacus erithacus), and in fowls, pigeons, turkeys, pheasants, partridges, grouse, woodpeckers, black-birds, starlings, and quails.

The parasite (Fig. 202).—The strobila attains 25 to 30 cm. in length by 1·4 mm. in breadth, and is composed of 500 to 600 proglottides. The scolex is provided with four large round suckers and a retractile rostellum surrounded by five concentric rings of hooklets, about 110 in all, 18 μ long. The rostellum when invaginated forms a kind of pouch which gives it the appearance of an apical sucker. In a recent communication Blanchard states that not only is the rostellum armed, but the suckers also are provided with hooklets. The neck is very wide, thick, depressed antero-posteriorly and furrowed laterally. The proximal segments are broader than long, the distal longer than broad (2 by 1·4 mm.). The last 100 proglottides are gravid and form one-half the length of the entire strobila. They resemble apple-seeds in shape. The genital pores are unilateral and open near the proximal corner of each segment. The cirrus pouch is fusiform, the ductus ejaculatorius very long and sinuous, the testicles over 50 in number. The receptaculum seminis is unusually long and broad; it extends to the middle of the segment and communicates with the oviduct. The uterus is composed of a number of tubes rolled up on each side into an almost spherical coil. When filled with ova the windings of the uterus unroll and extend throughout the proglottis; they then lose their walls, so that the eggs come to lie free in the parenchyma. The eggs then become surrounded, singly or in small groups, by parenchymatous cells forming egg-balls, of which from 300 to 400 may be present in each segment. The globular onchosphere (8 μ to 15 μ) is surrounded by two perfectly transparent shells, the outer one bearing two pointed projections.

Fig. 203.—Davainea asiatica, sagittal section of gravid segment. (After Linstow.)

The cystic stage is unknown. Blanchard suggests that it might be found in cockroaches (Periplaneta orientalis, P. americana, etc.). He points out that the parasite has a wide distribution within the tropics, and that cases of infection have occurred in islands, in seaports, and on board ship. The cockroach is cosmopolitan in distribution, it infests ships and contaminates food. Other tapeworms of the genus Davainea are known to spend their larval stage in insects and molluscs. According to Grassi and Revelli, some of these tapeworms—as, for instance, D. proglottina of fowls—may dispense with an intermediary invertebrate host and spend both their larval and adult stages within the body of the same host.

Pathogenesis.—We know nothing of the pathogenesis of this form of tæniasis. The parasite has been found almost exclusively in young children.

DAVAINEA ASIATICA (Linstow, 1901)

Synonym.—Tœnia asiatica.

History.—Davainea asiatica was described by Linstow in 1901, from a specimen in the Zoological Museum of the Imperial Academy of Science in St. Petersburg. It was passed by a man in Aschabad (Asiatic Russia, near the northern frontier of Persia), and preserved by Anger.

The parasite(Fig. 203).— The specimen examined by Linstow measures 29'S cm. in length, and is composed of 750 segments. The scolex is missing. The proglottides are all broader than long, measuring 0.16 mm. in width at the proximal end, and 1.78 mm. at the distal end. The posterior margin of each segment extends over the anterior margin of the next following segment. The genital pores are unilateral and open in the proximal third of each proglottis. The testicles (35 to 44 μ in diameter) are arranged in a ventral and dorsal layer of about eight rows each. The vas deferens extends in convolutions about one-third across the segment; the cirrus pouch is pyriform; the ovary extends across the segment between the ventral canals. The vagina forms a large fusiform receptaculum seminis. The uterus breaks up into 60 to 70 egg-balls in each segment. Mature eggs were not observed.

The cystic form is unknown.

INTESTINAL MYIASIS

A residence in the alimentary canal of some vertebrate animal is a regular feature in the life-history of many dipterous insects. The ova of the insect are either licked from the skin, or swallowed in the food on which they had been deposited. In this way they get transferred to the stomach, where, after a time, the larvae are hatched out and undergo development. In due course they appear in the fæces. Man is not infrequently victimized in this way, especially in tropical countries. Sometimes, until a correct diagnosis is arrived at, not a little alarm is caused by the appearance of these creatures in the stools. They are easily recognized. The ringed, cylindrical body, from ½ in. to 1 in. in length according to species, broad at one end, tapering at the other, and usually beset with little spines or hairs, is sufficiently diagnostic. (Fig. 204.)

Already we know over twenty species of diptera whose larvæ have been found in or expelled from the human intestinal canal. In Europe the majority of cases of intestinal myiasis, a not infrequent occurrence, are caused by Fannia canicularis (a fly closely resembling the common house-fly and erroneously considered a young form of the latter on account of its smaller size), and the closely related F. scalaris. Austen believes that intestinal myiasis, due to the larvæ of these flies, is probably to be traced to the parent flies having oviposited on the anus when the patient has been using some country privy where such insects are common.

A dose of castor oil will probably suffice to expel any of these creatures that may not have been passed spontaneously.

A rational prophylaxis would consist in the covering up of food after it has been cooked, in order to prevent the access of flies.

Instances in which the larvæ have been discharged per urethram have also been met with, though more rarely.

Fig. 204.—Larva of Calliphora vomitoria.

1. ↑ Stitt has pointed out that there are not really two separate spicules, but that two are united together to form one terminal prong.

2. ↑ * Bass considers that by the usual microscopical examination of fæces quite 20 per cent, of infections with A. duodenale are missed; he recommends examination of fæces as follows: "A quantity of fæces is well diluted with water, 1 to 10, and strained through gauze to get rid of coarse particles. It is then centrifuged and the fluid poured off, the centrifuge tube being refilled and centrifuged again until all the diluted fæces have been used. The precipitate is rewashed several times with water as long as anything can be washed out. Calcium chloride solution of a specific gravity of 1050 is now added and the precipitate washed as before. This salt is preferable to others because of its hygroscopic properties, and its addition to the fæces disposes of everything having a specific gravity below 1050. The precipitate is now examined, and will be found to contain most of the eggs which were present in the whole amount of original fæces."

3. ↑ * An anti-hookworm— as the ankylostome is called in America —campaign is now being waged in the United States and elsewhere, financed by Mr. Rockefeller. State and county dispensaries for free examination and treatment of applicants have been established. The total number treated in 11 States in 1912 was 238,755; the cost works out at a little over a dollar per head.

4. ↑ These experiments have recently been confirmed by Fülleborn, who found larvæ in the tracheal secretion of the tracheotomized and artificially infected dog.

5. ↑ The term cercocystis was introduced by Villot to designate those cysticercoids which are provided with caudal appendages.

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Table of Contents

Title page

Tropical Diseases — Chapter 45 : Intestinal Parasites

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