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As strains of bird flu appear in livestock in Africa, we ask the experts to give the lowdown on the disease

 

What is avian influenza (bird flu)?

Bird flu is an infection caused by avian (bird) influenza
(flu) viruses. These flu viruses occur naturally among
birds. Wild birds worldwide carry the viruses in their
intestines, but usually do not get sick from them.
However, bird flu is very contagious among birds and can
make some domesticated birds, including chickens, ducks,
and turkeys, very sick and kill them.

Do bird flu viruses infect humans?

Bird flu viruses do not usually infect humans, but several
cases of human infection with bird flu viruses have
occurred since 1997.

How are bird flu viruses different from human flu
viruses?

There are many different subtypes of type A influenza
viruses. These subtypes differ because of certain proteins
on the surface of the influenza A virus (hemagglutinin
[HA] and neuraminidase [NA] proteins).

There are 16 different HA subtypes and 9 different NA
subtypes of flu A viruses. Many different combinations of
HA and NA proteins are possible. Each combination is a
different subtype. All known subtypes of flu A viruses can
be found in birds.

However, when we talk about “bird flu” viruses, we are
referring to influenza A subtypes chiefly found in birds.
They do not usually infect humans, even though we know
they can. When we talk about “human flu viruses” we are
referring to those subtypes that occur widely in humans.

There are only three known A subtypes of human flu
viruses (H1N1, H1N2, and H3N2); it is likely that some
genetic parts of current human influenza A viruses came
from birds originally. Influenza A viruses are constantly
changing, and they might adapt over time to infect and
spread among humans.

What are the symptoms of bird flu in humans?

Symptoms of bird flu in humans have ranged from typical
flu-like symptoms (fever, cough, sore throat and muscle
aches) to eye infections, pneumonia, severe respiratory
diseases (such as acute respiratory distress), and other
severe and life-threatening complications. The symptoms
of bird flu may depend on which virus caused the infection.


How does bird flu spread?

Infected birds shed flu virus in their saliva, nasal
secretions, and feces. Susceptible birds become infected
when they have contact with contaminated excretions or
surfaces that are contaminated with excretions.

It is believed that most cases of bird flu infection in
humans have resulted from contact with infected poultry
or contaminated surfaces. The spread of avian influenza
viruses from one ill person to another has been reported
very rarely, and transmission has not been observed to
continue beyond one person.

How is bird flu in humans treated?

Studies done in laboratories suggest that the prescription
medicines approved for human flu viruses should work in
preventing bird flu infection in humans. However, flu
viruses can become resistant to these drugs, so these
medications may not always work. Additional studies are
needed to prove the effectiveness of these medicines.

What is the risk to humans from bird flu?

The risk from bird flu is generally low to most people
because the viruses occur mainly among birds and do not
usually infect humans.

However, during an outbreak of bird flu among poultry
(domesticated chicken, ducks, turkeys), there is a
possible risk to people who have contact with infected
birds or surfaces that have been contaminated with
excretions from infected birds.

The current outbreak of avian influenza A (H5N1) among
poultry in Asia and Europe (see below) is an example of a
bird flu outbreak that has caused human infections and
deaths. In such situations, people should avoid contact
with infected birds or contaminated surfaces, and should
be careful when handling and cooking poultry.

In rare instances, limited human-to-human spread of
H5N1 virus has occurred, and transmission has not been
observed to continue beyond one person.

What is an avian influenza A (H5N1) virus?

Influenza A (H5N1) virus – also called “H5N1 virus” – is an
influenza A virus subtype that occurs mainly in birds. It
was first isolated from birds (terns) in South Africa in
1961. Like all bird flu viruses, H5N1 virus circulates among
birds worldwide, is very contagious among birds, and can
be deadly.

What is the H5N1 bird flu that has been reported in Asia
and Europe?

Outbreaks of influenza H5N1 occurred among poultry in
eight countries in Asia (Cambodia, China, Indonesia, Japan,
Laos , South Korea , Thailand , and Vietnam) during late
2003 and early 2004.

At that time, more than 100 million birds in the affected
countries either died from the disease or were killed in
order to try to control the outbreak. By March 2004, the
outbreak was reported to be under control. Beginning in
late June 2004, however, new outbreaks of influenza H5N1
among poultry were reported by several countries in Asia
(Cambodia, China [ Tibet ], Indonesia, Kazakhastan,
Malaysia, Mongolia, Russia [ Siberia ], Thailand, and
Vietnam).

It is believed that these outbreaks are ongoing. Most
recently, influenza H5N1 has been reported among poultry
in Turkey and Romania. Human infections of influenza A
(H5N1) have been reported in Cambodia, Indonesia,
Thailand, and Vietnam.

What is the risk to humans from the H5N1 virus in Asia
and Europe?

The H5N1 virus does not usually infect humans. In 1997.
However, the first case of spread from a bird to a human
was seen during an outbreak of bird flu in poultry in Hong
Kong, Special Administrative Region.

The virus caused severe respiratory illness in 18 people, 6
of whom died. Since that time, there have been other cases
of H5N1 infection among humans. Recent human cases of
H5N1 infection that have occurred in Cambodia, Thailand,
and Vietnam have coincided with large H5N1 outbreaks in
poultry.

The World Health Organization (WHO) also has reported
human cases in Indonesia. Most of these cases have
occurred from contact with infected poultry or contaminated
surfaces; however, it is thought that a few cases of
human-to-human spread of H5N1 have occurred.

So far, spread of H5N1 virus from person to person has
been rare and has not continued beyond one person.
However, because all influenza viruses have the ability to
change, scientists are concerned that the H5N1 virus one
day could be able to infect humans and spread easily from
one person to another.

Because these viruses do not commonly infect humans,
there is little or no immune protection against them in the
human population. If the H5N1 virus were able to infect
people and spread easily from person to person, an
influenza pandemic (worldwide outbreak of disease) could
begin.

No one can predict when a pandemic might occur. However,
experts from around the world are watching the H5N1
situation in Asia very closely and are preparing for the
possibility that the virus may begin to spread more easily
and widely from person to person.

How is infection with H5N1 virus in humans treated?

The H5N1 virus currently infecting birds in Asia that has
caused human illness and death is resistant to amantadine
and rimantadine, two antiviral medications commonly used
for influenza. Two other antiviral medications, oseltamavir
and zanamavir, would probably work to treat flu caused by
the H5N1 virus, but additional studies still need to be done
to prove their effectiveness.

Is there a vaccine to protect humans from H5N1 virus?

There currently is no commercially available vaccine to
protect humans against the H5N1 virus that is being seen in
Asia and Europe . However, vaccine development efforts
are taking place. Research studies to test a vaccine to
protect humans against H5N1 virus began in April 2005, and
a series of clinical trials is underway. For more information
about the H5N1 vaccine development process, visit the
National Institutes of Health website.

What is the risk to people in North America, the
Caribbean and Africa from the H5N1 bird flu outbreak in
Asia and Europe ?

The current risk to people living in other parts of the globe
from the H5N1 bird flu outbreak in Asia is low. The strain of
H5N1 virus found in Asia and Europe has not been found in
the United States or Canada.

There have been no human cases of H5N1 flu in Africa,
South America and the West Indies . It is possible that
travelers returning from affected countries in Asia could be
infected if they were exposed to the virus.

Many thanks to the United States' Department of Health and
the Hong Kong Government

For more information about avian influenza and food safety
issues, visit the
World Health Organization website

The Lowdown on Avian Flu

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