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Avian flu
is a virulent viral disease affecting poultry and other birds in
Asia.
It is also called "bird flu." A highly pathogenic strain, H5N1, has been
persistent and tenacious, spreading rapidly through poultry with a
mortality approaching 100% within 48 hours.. Despite the fact that an
estimated 150 birds have died or been destroyed, the virus has become
endemic in some areas and is being spread by migratory birds.
It has caused a small number of cases of flu and even some deaths in
people who have been in direct contact with infected birds. No cases of
sustained human-to-human transmission have been established as of June
2006; however, scientists are concerned that the avian flu virus may
mutate and become transmissible between humans. Avian flu virus has not
been found in the U.S.
In
1918, 1957 and 1968 the flu season in the U.S. was especially severe, and
resulted in a much higher number of illnesses and deaths. This more
dangerous form is called pandemic flu. Public health experts
believe that a flu pandemic is likely to occur again in the future.
Scientists worry that a mutant form of avian flu, under certain
circumstances, could eventually cause a flu pandemic-- although this
scenario may never happen.
Which
countries have been affected by outbreaks in poultry?
Since
2003, outbreaks have been reported in 14 countries: the Republic of Korea,
Viet Nam, Japan, Thailand, Cambodia, Lao People’s Democratic Republic,
Indonesia, China. Malaysia, Mongolia, Russia, Turkey and Romania.
What are the implications of avian influenza to human health?
Widespread persistence of H5N1 in poultry populations poses two main risks
for human health.
1) the risk of direct infection when the virus passes from the infected
bird to humans, sometimes resulting in severe disease; and
2) the risk that the virus – if given enough opportunities – will change
into a form that is highly infectious for humans and spreads easily from
person to person.
Human cases of influenza A (H5N1) infection have been reported in
Azerbaijan, Cambodia, China, Djibouti, Egypt, Indonesia, Iraq, Thailand,
Turkey, and Vietnam. For the most current information about avian
influenza and cumulative case numbers, see the
World Health Organization Avian Influenza
website.
What are the risks to humans from the current H5N1 outbreak?
H5N1 virus does not usually infect people, but more than 200 human cases
have been reported. Most of these cases have occurred from direct or close
contact with infected poultry or contaminated surfaces by their feces.
Expsoure to the virus is likely during slaughter, de-feathering,
butchering and preparing poutry fo rcooking. Currently, there is no
evidence that properly cooked poultry or eggs are a source of infection.
So far, spread of H5N1 virus from person to person has been rare and has
not continued beyond one person. Nonetheless, because all influenza
viruses have the ability to change, scientists are concerned that 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 H5N1 virus were to gain the capacity to 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 and Europe very closely and are preparing for the
possibility that the virus may begin to spread more easily from person to
person.
What changes are needed for the H5N1 virus to affect humans and become
pandemic?
The virus has presently infected humans through a ‘bird–to–human’
transmission. However, the establishment of efficient and sustained
human-to-human transmission of the virus has not occurred. For this to
take place, the H5N1 virus would need to improve its transmissibility
among humans.
The virus can become transmissible among humans by either ‘reassortment’
or adapative mutation. Reassortment occurs when genetic material is
exchanged between human and avian viruses during co-infection (infection
with both viruses at the same time) of a human or another mammal. The
result could be a fully transmissible pandemic virus—that is, a virus that
can spread easily and directly between humans. A more gradual process is
adaptive mutation, where the capability of a virus to bind to human cells
increases during infections of humans.
Are vaccines and antivirals available for prevention and treatment?
Some
clinical trials are currently underway. Because the vaccine needs to
closely match the pandemic virus, large-scale commercial production will
not start until the new virus has emerged and a pandemic has been
declared. Current global production capacity falls far short of the demand
expected during a pandemic.
Two antiviral medications, oseltamivir (commercially known as Tamiflu) and
zanamivir (commercially known as Relenza) can reduce the severity and
duration of illness caused by seasonal influenza.
For cases of human infection with H5N1, these same drugs may improve
prospects of survival, if administered early, but clinical data are
limited. The main constraints – which are substantial – involve limited
production capacity and a price that is prohibitively high for many
countries. At present manufacturing capacity, which has recently
quadrupled, it will take a decade to produce enough oseltamivir to treat
20% of the world’s population. The manufacturing process for oseltamivir
is complex and time-consuming, and is not easily transferred to other
facilities. These medications will also be used to prevent those who have
yet to be exposed to help decrease the number of cases when exposure has
occurred.
Is there a risk in handling feather products that come from countries
experiencing outbreaks of avian influenza A (H5N1)?
The U.S. government has determined that there is a risk to handling
feather products from countries experiencing outbreaks of H5N1 influenza.
There is currently a ban on the importation of birds and bird products
from H5N1-affected countries in Africa, Asia, and Europe. The
regulation states that no person may
import or attempt to import any birds (Class Aves), whether dead or alive,
or any products derived from birds (including hatching eggs), from the
specied countries (see
Embargo of Birds from Specified Countries
Does CDC recommend travel restrictions to areas with known H5N1 outbreaks?
CDC does not recommend any travel restrictions to affected countries at
this time. However, CDC currently advises that travelers to countries with
known outbreaks of H5N1 influenza 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. Recommendations
include avoiding direct contact with birds, pooutry and livestock and
easting only poultry and eggs that have been thoroughly cooked.
The World Health Organization (WHO), the CDC and the U.S. Department of
State issue travel information, alert, warnings and announcements for
public safety, personal security and health issues. Before you travel
internationally please consult the sites below. For more international
travel health information, see:
Precautions
for International Travelers returning to the United States:
If you have recently lived in, or traveled from, an area
where avian flu is present and you now have a fever, headache, muscle
aches or respiratory symptoms, you should call a health care provider and
ask for instructions.
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