Avian Influenza

Definition

Avian influenza, or bird flu, is a form of flu caused by a strain of the influenza

A virus that ordinarily affects only birds. Avian influenza is considered

a zoonosis because it can be transmitted from animals to humans.

It is also considered an emerging disease because it has been identified

as a major public health problem within the last twenty years and threatens

to get worse in the near future.

Wild birds carry many types of the influenza A virus in their digestive

tract but do not usually get sick from it. Infected wild birds can, however,

infect chickens, turkeys, and other domesticated birds through contact

with their nasal secretions or droppings. The infection can be spread by

contaminated bird feed, water, or soil as well as by direct contact between

wild birds and domesticated poultry. There are

two subtypes of avian flu in birds: a relatively

mild form that causes symptoms such as feather

loss and a severe form that can kill entire flocks

of chickens, geese, or turkeys within forty-eight

hours.

Most cases of avian flu in humans as of

2008 have occurred in farmers or other people

who were exposed to sick birds. There are very

few cases of human-to-human transmission of

this form of influenza. The primary reason for

concern is that one specific form of the flu virus

that causes avian flu

widespread sickness and death if it mutates into

a form that can spread easily and directly from

human to human. It was a different form of the

influenza A virus (H1N1) that caused the flu

pandemic of 1918

of millions of people worldwide.

—H5N1—could cause–1920, which took the lives

Description

Avian influenza is similar to seasonal influenza. The person develops a

cough, a fever, an inflammation of the tissues lining the eyelid, a runny

nose, and a headache. The incubation period in humans varies between

two and seventeen days, with five days being the most common length

of time. In fatal cases, the patient begins to have trouble breathing and

may cough up blood about five days after symptoms of illness appear.

Death usually results from viral pneumonia.

Some patients also have abdominal pain, vomiting, and bloody diarrhea

in addition to respiratory symptoms.

Demographics

The first cases of bird flu in humans were reported in Hong Kong in

1997. Of the eighteen people taken ill, six died from the infection. The

disease has spread westward among the bird populations of Asia, Europe,

and northern Africa, with cases of human illness following. In Europe,

however, there have been instances of infected birds discovered without

any cases of human disease. As of September 10, 2008, the World Health

Organization (WHO) reported that 387 confirmed cases of avian influenza

in humans have occurred since 2003; more than half of the patients died.

There have been no confirmed cases of avian influenza caused by the

H5N1 subtype in the United States in either birds or humans as of September

2008. There were, however, outbreaks of a different flu virus among

American poultry in 2003 and 2004. Given the fact that the broadened

spread of any subtype of flu virus increases the danger to public health in

all countries around the world, many researchers think that it is only a

matter of time until the H5N1 type of avian flu reaches the United States.

The risk factors for getting bird flu are not completely understood,

although contact with infected birds or their droppings appears to be the

single most important factor.

•

be infected.

People of all races and both genders appear to be equally likely to

•

are most likely to die from avian flu if they become infected.

According to WHO, people between the ages of ten and thirtynine

•

twenty years of age or younger; 40 percent of cases have been

reported in people between twenty and forty years of age.

As of 2008, 50 percent of reported cases have been in people

Causes and Symptoms

The cause of avian influenza in humans is a variant of the H5N1 influenza

virus that has somewhat adapted itself to infecting people. There is

some evidence that the same strain that infects birds also infects pigs and

can jump the species barrier into humans from pigs as well as birds.

Avian influenza may affect the lower airway in humans more severely

than seasonal influenza. The most common symptoms are:

•

Fever above 100.4°F (38°C)

•

Cough

•

Sore throat

•

Difficulty breathing

•

Headache

•

Conjunctivitis (inflammation of the tissues lining the eyelid)

Diagnosis

Diagnosis of suspected cases of avian flu was complicated until 2006

because samples of the patient

health laboratories or the Centers for Disease Control and Prevention

(CDC) in Atlanta, Georgia, for analysis. In February 2006, however, the

Food and Drug Administration (FDA) approved a new test for diagnosing

strains of bird flu in people who might have the virus. The test

is called the Influenza A/H5 (Asian lineage) Virus Real-time RT-PCR

Primer and Probe Set. The test gives results within four hours.

Treatment

The CDC recommends two antiviral drugs, Tamiflu and Relenza, for

treating any suspected case of bird flu in the United States. It is not

known, however, whether the H5N1 influenza virus might become resistant

to these drugs. In addition, the drugs must be taken within two days

of the appearance of symptoms to be fully effective. Two experimental

antiviral drugs were being tested in Russia and China in 2008, but

neither had yet become available in the United States.

Patients with a severe case of avian influenza may need to be placed

on a respirator. In addition, public health officials currently recommend

that patients suspected of having avian flu should be placed in isolation to

reduce the risk of the infection spreading to other people.

Prognosis

Avian influenza in humans is a serious disease, with a mortality rate close

to 60 percent. There is little information available about the long-term

effects of the illness on survivors.

Prevention

There was no effective vaccine against avian influenza that was available

to the general public in late 2008, although some were undergoing clinical

trials. One of the difficulties of producing a vaccine against this type

of flu in large quantities is that the virus is so powerful that it cannot

easily be cultured in chicken eggs, which is the usual method for making

vaccines. In June 2008, the

an experimental vaccine that produced a satisfactory immune response in

75 percent of the subjects who were injected with it. The vaccine

appeared to be safe for widespread use in humans and could be made

in cell cultures rather than in eggs.

Until an effective vaccine for avian flu is available, the most important

preventive measures people can take are to wash their hands

frequently and avoid open-air markets, raw or undercooked eggs or

poultry, and close contact with live poultry when visiting Asia or other

countries where cases of avian flu have been reported. Travelers may also

want to ask their doctor about getting a flu shot before they take their

trip. Standard flu shots will not prevent bird flu, but they can protect

people against being infected with seasonal flu.

The Future

Because of the potential disaster of an avian influenza pandemic,

researchers are working on developing new antiviral medications and

effective vaccines as quickly as possible. No one knows if or when the

H5N1 virus will mutate into a form that can be easily transmitted from

one person to another. Public health officials around the world are

hoping that they will be prepared if that mutation does occur.

SEE ALSO

Influenza; Pneumonia; Severe acute respiratory syndrome

For more information

BOOKS

Goldsmith, Connie.

First Century Books, 2007. Chapter 6 is about avian influenza.

Grady, Denise.

Fever to Avian Flu

Siegel, Marc.

Hoboken, NJ: Wiley, 2006.

Influenza: The Next Pandemic? Minneapolis, MN: Twenty-Deadly Invaders: Virus Outbreaks around the World, from Marburg. Boston, MA: Kingfisher, 2006.Bird Flu: Everything You Need to Know about the Next Pandemic.

WEB SITES

Center for Food Safety and Applied Nutrition (CFSAN).

to Know about Avian Influenza

~dms/avfluqa.html (updated October 19, 2006; accessed September 14,

2008). This page provides basic information about the safe preparation of

foods containing eggs or poultry.

Centers for Disease Control and Prevention (CDC).

Home Page

7, 2007; accessed September 13, 2008).

KidsHealth.

health_problems/infection/bird_flu.html (updated February 2007; accessed

September 14, 2008).

Mayo Clinic.

com/health/bird-flu/DS00566 (updated July 11, 2008; accessed September

13, 2008).

National Institute of Allergy and Infectious Diseases (NIAID).

Flu, Avian (Bird) Flu, and Pandemic Flu?

www3.niaid.nih.gov/topics/Flu/understandingFlu/DefinitionsOverview.htm

(updated November 28, 2006; accessed September 14, 2008).

National Library of Medicine (NLM).

online at http://www.nlm.nih.gov/medlineplus/tutorials/avianflu/htm/index.

htm (accessed September 14, 2008). This is an online tutorial with voiceover;

viewers have the option of a self-playing version, a text version, or an interactive

version with questions.

Public Broadcasting Service (PBS).

online at http://www.pbs.org/wgbh/amex/influenza/index.html

(accessed September 14, 2008). Web site includes a transcript of the television

program, a timeline and interactive maps, and reflections by a presentday

scientist on the possibility of another pandemic.Avian Influenza (Bird Flu). Available online at http://www.cdc.gov/flu/avian/ (updated MayBird Flu (Avian Flu). Available online at http://kidshealth.org/kid/Bird Flu (Avian Influenza). Available online at http://www.mayoclinic.What Are SeasonalAvailable online at http://Avian Influenza or Bird Flu. AvailableAmerican Experience: Influenza 1918. AvailableWhat Consumers Need. Available online at http://www.cfsan.fda.gov/New England Journal of Medicine reported on’s throat secretions had to be sent to state

Avian Influenza