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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.
H5N1could cause1920, 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. Available
What Consumers Need. Available online at http://www.cfsan.fda.gov/
New England Journal of Medicine reported on
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Avian Influenza