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. For more information about
avian influenza and food safety issues, visit
the
World Health Organization website. 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. 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 the United
States from the H5N1 bird flu outbreak in Asia
and Europe ?
The current risk to Americans 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 . There have been no
human cases of H5N1 flu in the United States .
It is possible that travelers returning from
affected countries in Asia could be infected if
they were exposed to the virus. Since February
2004, medical and public health personnel have
been watching closely to find any such cases.
What does CDC recommend regarding the H5N1
bird flu outbreak?
In February 2004, CDC provided U.S. health
departments with recommendations for enhanced
surveillance (“detection”) in the U.S. of avian
influenza A (H5N1). Follow-up messages,
distributed via the Health Alert Network, were
sent to the health departments on August 12,
2004 , and February 4, 2005 ; both alerts
reminded health departments about how to detect
(domestic surveillance), diagnose, and prevent
the spread of avian influenza A (H5N1). The
alerts also recommended measures for laboratory
testing for H5N1 virus. CDC currently advises
that travelers to countries with known outbreaks
of influenza A (H5N1) avoid poultry farms,
contact with animals in live food markets, and
any surfaces that appear to be contaminated with
feces from poultry or other animals. CDC does
not recommend any travel restrictions to
affected countries at this time. For more
information, visit
Travelers' Health.
What is CDC doing to prepare for a possible
H5N1 flu pandemic?
CDC is taking part in a number of pandemic
prevention and preparedness activities,
including:
- Providing leadership to the National
Pandemic Influenza Preparedness and Response
Task Force, created in May 2005 by the
Secretary of the U.S. Department of Health
and Human Services.
- Working with the Association of Public
Health Laboratories on training workshops
for state laboratories on the use of special
laboratory (molecular) techniques to
identify H5 viruses.
- Working with the Council of State and
Territorial Epidemiologists and others to
help states with their pandemic planning
efforts.
- Working with other agencies such as the
Department of Defense and the Veterans
Administration on antiviral stockpile
issues.
- Working with the World Health
Organization (WHO) and Vietnamese Ministry
of Health to investigate influenza H5N1 in
Vietnam and to provide help in laboratory
diagnostics and training to local
authorities.
- Performing laboratory testing of H5N1
viruses.
- Starting a $5.5 million initiative to
improve influenza surveillance in Asia .
- Holding or taking part in training
sessions to improve local capacities to
conduct surveillance for possible human
cases of H5N1 and to detect influenza A H5
viruses by using laboratory techniques.
- Developing and distributing reagents
kits to detect the currently circulating
influenza A H5N1 viruses.
Working together with WHO and the National
Institutes of Health (NIH) on safety testing of
vaccine seed candidates and to develop
additional vaccine virus seed candidates for
influenza A (H5N1) and other subtypes of
influenza A virus. |
