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In the month of May 2003, in Thailand, hundred of chickens died of Bird Flu at a
research centre in its northern part. The Avian influenza virus swept through
ten Asian countries killing more than 100 million poultry including more than
373 million in Thailand.
DIFFERENT STRAINS OF FLU
Flu virus are RNA animal viruses. An individual virus resembles a rod studded
with spikes composed of two kinds of proteins. There are three general types of
flu virus viz. Type A, Type B, Type C distinguished by capsid protein, which is
different for each type.
Different strains of flu virus are different in their protein spikes.
Hemagglutinin (H) - helps virus to access the host cell.
Neuraminidace (N) - helps the daughter cell virus to break free of the host
cell, once the virus replication has been completed.
H molecule in virus responsible for the mutations & the mutations is transported
to generations. Because of accumulating changes in H & N molecules, different
sub-types of flu viruses are formed Different flu vaccines are needed for the
protection against different sub-types.
e.g. Type A virus has thirteen distinct H- subtypes & nine distinct N types,
each of which requires a different vaccine.
WHY BIRD FLU ARISES OFTEN IN ASIA:
The most common hosts for influenza virus are ducks, chickens & pigs which in
Asia live in the close proximity to humans. Pigs are subjected to infections by
birds as well as human strains of virus. Individual animals are often infected
by multiple strains simultaneously. This creates a conditions favoring genetic
re-combination between strains producing new combinations of H & N subtypes.
A(H5 N1) TYPE BIRD FLU VIRUS:-
A potentially deadly, new strain of flu virus, A(H5 N1) has emerged in Hong
Kong. Scientists for two reasons greeted its arrival with unusual caution-
(1) A (H5 N1) represents a combination of H&N spikes, which has been, associated
with past flu epidemics.
(2) A (H5 N1) passes to humans directly from bird.
For the 1 st time A (H5 N1) virus was detected in chicken in 1961 & for the 2 nd
time in 1997 in Hong Kong. The first human case of A (H5 N1) was a
three-year-old boy who died. By 2004, 17 cases were reported. Five were dead &
three struggled for life in ICUs & survived with the aid of mechanical
respirators. Fortunately, bird flu virus does not appear to spread easily from
person to person. Public health officials are worried whether the genes of A (H5
N1) can get mixed with the human strains to create a new strain or not.
Thousands of Blood Samples from people have been taken for tests in labs.
Some of the important facts about the bird flu viruses are:
- Humans can only contract the virus if they have close contact with the live
infected poultry.
- Well-cooked eggs and chicken are safe as virus is killed at 50-60 degrees
Celsius.
- Standard control measure is to kill the infected or potentially exposed chicken.
- Stringent sanitary measures on the farm can protect the farmers to an extent
In late July 2005, official reports to the OIE from government authorities
indicated that the H5N1 virus has expanded its geographical range. Both Russia
and Kazakhstan reported outbreaks of avian influenza in poultry in late July,
and confirmed H5N1 as the causative agent in early August. These are the first
outbreaks of highly pathogenic H5N1 avian influenza recorded in the two
countries. Both countries were previously considered free of the virus. In early
August, Mongolia issued an emergency report following the death of 89 migratory
birds at two lakes in the northern part of the country. Avian influenza virus
type A has been identified as the cause, but the virus strain has not yet been
determined. Samples have been shared with WHO reference laboratories and are
currently being investigated. Also in early August, an outbreak of H5N1 in
poultry was detected in Tibet , China . In all of these recent outbreaks,
authorities have announced control measures in line with FAO and OIE
recommendations for highly pathogenic avian influenza. To date, no human cases
have been detected, vigilance is high, and rumours are being investigated by
local authorities.
On 6 August, government scientists at the US National Institute of Allergy and
Infectious Diseases announced results from initial clinical trials of a vaccine
being developed to protect humans against infection with H5N1 avian influenza.
Preliminary data indicate that the experimental vaccine evoked an immune
response in a small group of healthy adults. Although more trials are needed,
the new findings reconfirm the feasibility of developing an H5N1-specific
vaccine. Vaccines are the principal medical intervention for protecting
individuals against pandemic influenza. If available rapidly and in sufficient
quantities, they can reduce the morbidity and mortality that have traditionally
made pandemics such socially disruptive as well as deadly events.
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