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.
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Do
bird flu viruses infect humans?
Bird flu viruses do not usually infect humans, but more than
100 confirmed cases of human infection with bird flu viruses
have occurred since 1997. For example, the World Health Organization
(WHO) maintains situation updates and cumulative reports of
human cases of avian influenza A (H5N1). Please visit the
WHO links for additional information, as well as links to
previous situation updates and cumulative reports.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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 (Centers for Disease Control and Prevention).
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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.
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.
(Source: Centers
for Disease Control and Prevention) |
