Bird flu basics
Bronstein / Getty Images
rapid spread of bird flu, which is not
uncommon among chickens and other fowl,
has caught the attention of global
health authorities. Click on the topics
to learn more about the illness and why
scientists are so concerned.
|There are at least 15
different types of avian influenza that
routinely infect birds around the world.
The current outbreak is caused by a
strain known as H5N1, which is highly
contagious among birds and rapidly
fatal. Unlike many other strains of
avian influenza, it can be transmitted
to humans, causing severe illness and
Bird flu is not the same as SARS
(severe acute respiratory syndrome).
Although their symptoms are similar,
SARS is caused by completely different
viruses. Influenza viruses also are more
contagious and cannot be as readily
contained as SARS by isolating people
who have the infection.
|Influenza viruses are
highly unstable and have the ability to
mutate rapidly, potentially jumping from
one animal species to another.
Scientists fear the bird flu virus could
evolve into a form that is easily spread
between people, resulting in an
extremely contagious and lethal disease.
This could happen if someone already
infected with the human flu virus
catches the bird flu. The two viruses
could recombine inside the victim’s
body, producing a hybrid that could
readily spread from person to person.
The resulting virus likely would be
something humans have never been exposed
to before. With no immune defenses, the
infection could cause devastating
illness, such as occurred in the 1918-19
Spanish flu pandemic, which killed an
estimated 40 million to 50 million
|In rural areas, the H5N1
virus is easily spread from farm to farm
among domestic poultry through the feces
of wild birds. The virus can survive for
up to four days at 71 F (22 C) and more
than 30 days at 32 F (0 C). If frozen,
it can survive indefinitely.
So far in this outbreak, human cases
have been blamed on direct contact with
infected chickens and their droppings.
People who catch the virus from birds
can pass it on to other humans, although
the disease is generally milder in those
who caught it from an infected person
rather than from birds.
If the virus mutates and combines
with a human influenza virus, it could
be spread through person-to-person
transmission in the same way the
ordinary human flu virus is spread.
|The current outbreak of
bird flu is different from earlier ones
in that officials have been unable to
contain its spread. An outbreak in 1997
in Hong Kong was the first time the
virus had spread to people, but it was
much more quickly contained. A total of
18 people were hospitalized with six
reported deaths. About 1.5 million
chickens were killed in an effort to
remove the source of the virus.
Unlike the 1997 scare, this outbreak
has spread more rapidly to other
countries, increasing its exposure to
people in varied locations and raising
the likelihood that the strain will
combine with a human influenza virus.
|Bird flu can cause a
range of symptoms in humans. Some
patients report fever, cough, sore
throat and muscle aches. Others suffer
from eye infections, pneumonia, acute
respiratory distress and other severe
and life-threatening complications.
|Flu drugs exist that may
be used both to prevent people from
catching bird flu and to treat those who
have it. The virus appears to be
resistant to two older generic flu
drugs, amantadine and rimantadine.
However, the newer flu drugs Tamiflu and
Relenza are expected to work – though
supplies could run out quickly if an
Currently there is no vaccine,
although scientists are working to
develop one. It probably will take
several months to complete and may not
be ready in time to stop a widespread
human outbreak, if one occurs.
|Rapid elimination of the
H5N1 virus among infected birds and
other animals is essential to preventing
a major outbreak. The World Health
Organization recommends that infected or
exposed flocks of chickens and other
birds be killed in order to help prevent
further spread of the virus and reduce
opportunities for human infection.
However, the agency warns that safety
measures must be taken to prevent
exposure to the virus among workers
involved in culling.