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.
http://www.cdc.gov/flu/avian/gen-info/facts.htm |
