The
effect of Bird Flu on humans
Of the 15 subtypes known, only subtypes H5,
H7 and H9 are known to be capable of crossing the species
barrier from birds to humans. It is feared that if the avian
influenza virus undergoes antigenic shift with a human influenza
virus, the new subtype created could be both highly contagious
and highly lethal in humans. Such a subtype could cause a
global influenza pandemic, similar to the Spanish Flu that
killed over 20 million people in 1918 (though a variety of
sources quote average figures even higher, up to 100 million
in some cases).
Many health experts are concerned that a
virus that mutates to the point where it can cross the
species barrier (i.e. from birds to humans) will inevitably
mutate
to the point where it can be transmitted from human to
human. It is at that point that a pandemic becomes likely.
The
first cases of avian influenza passed from birds to humans
was H5N1 in 1997 in Hong Kong. 18 people were infected,
of
whom 6 died. The outbreak was limited to Hong Kong. All
chickens in the territory were slaughtered.
In January 2004,
a major new outbreak of H5N1 avian influenza surfaced in
Vietnam and Thailand's poultry industry, and
within weeks spread to ten countries and regions in Asia,
including
Indonesia, South Korea, Japan and mainland China. Intensive
efforts were undertaken to slaughter chickens, ducks
and geese (over 40 million chickens alone were slaughtered
in high-infection
areas), and the outbreak was contained by March, but
the
total human death toll in Vietnam and Thailand was 23
people. In
February 2004, avian influenza virus was detected in
pigs in Vietnam, increasing fears of the emergence of new
variant
strains.
Fresh outbreaks in poultry were confirmed in
Ayutthaya and Pathumthani provinces of Thailand, and Chaohu
city
in Anhui,
China, in July 2004.
In North America, the presence
of avian influenza was confirmed at several poultry farms
in British Columbia
in February
2004. As of April 2004, 18 farms have been quarantined
to halt the
spread of the virus. Two cases of humans with avian
influenza have been confirmed in that region.
In August
2004 avian flu was confirmed in Kampung Pasir, Kelantan,
Malaysia. Two chickens were confirmed
to
be carrying H5N1.
As a result Singapore has imposed a ban on the
importation of chickens and poultry products. Similarly the
EU
has imposed a ban on Malaysian poultry products.
A cull of
all poultry
has been ordered by the government within a 10km
radius of the location of this outbreak.
An outbreak
of avian influenza in January 2005 affected 33 out of 64
cities and provinces in Vietnam,
leading
to the
forced killing of nearly 1.2 million poultry.
Up to 140 million birds
are believed to have died or were killed because
of the outbreak. As of April 17, the outbreak
had claimed
at
least 50 human
lives - most in Vietnam.
Vietnam and Thailand
have seen several isolated cases where human-to-human transmission
of the
virus has
been suspected.
In one case the original carrier, who received
the disease from a bird, was held by her mother
for roughly
5 days
as the young girl died. Shortly afterwards,
the mother became
ill
and perished as well. In March, 2005 it was
revealed that two nurses who had cared for avian flu patients
have tested
positive
for the disease. |
