Warmer weather won’t put lid on H5N1 virus: experts

By Tan Ee Lyn

HONG KONG (Reuters) – The return of warmer weather to the
northern hemisphere is unlikely to bring a let-up in the deadly
H5N1 virus since it is already endemic in poultry flocks in
several parts of Asia, experts say.

Scientists previously found the bird flu virus to be most
active from October to March when temperatures are cooler or
below 20 Celsius (68 Fahrenheit), but now they are warning
against any complacency with the return of summer.

“I don’t think it will go away in the summer months, it
will continue to be in poultry,” said Hong Kong microbiologist
Malik Peiris, who has studied the virus since 1997, when it
made its first known jump to humans in Hong Kong, killing six
people.

“The virus has been persisting in quite diverse climates,
such as Indonesia, where it is hot … to a large extent it has
been maintained in poultry flocks.”

The virus resurfaced in late 2003 and has been seen in
birds in over 40 countries in Asia, Europe, the Middle East and
Africa. It spread quickly in the past two months, infecting 20
new countries.

Although the number of human infections from birds is low
at 204 cases, 113 have died and some experts say just a few
mutations are needed for the virus to transmit among people,
triggering a pandemic.

Outside Asia, human casualties have been most common in
Turkey and Egypt, where there have been 24 documented
infections and 8 deaths combined — or mortality rates of about
30 percent, which are lower than rates of 50 percent or more in
Asia.

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But the lower rates do not mean the virus has attenuated.

“In most places in Asia, it is only those which are
severely ill that get picked up for investigation. Those with
mild flu-like disease are not. You don’t see the milder cases
of H5N1, that skews your rate of severity and mortality,”
Peiris said.

“In Turkey … they may have picked up the milder cases.”

With the notable exception of China, human cases everywhere
have invariably occurred in areas with poultry outbreaks,
meaning the greatest direct threat is still chicken, and not
wild birds, which are blamed for spreading the virus over vast
distances.

Experts recommend speedy mass culling in areas with
outbreaks in birds and vaccination for poultry in surrounding
areas. But they worry about Egypt, Indonesia, India, China and
Africa.

“For countries with human cases, they are those who can’t
mount a completely effective response to bird flu, most notably
Egypt, Indonesia. There are few reports on Nigeria,” said Lo
Wing-lok, an infectious disease expert in Hong Kong.

“The cases in Egypt arose from contact with chickens, same
in Indonesia, where the government has given up on extensive
culling. The vaccination program is not as effective.”

Peiris said: “The reason why it is more manageable in
Europe is because you don’t have such large numbers of backyard
poultry and the poultry industry … is protected from wild
birds.”

“The lesson for Asia is: when you have early detection and
determined action, you can stamp it out. It will be interesting
to see if you are able to stamp it out in places like India.”

The appearance of human cases in China in places with no
reported bird outbreaks has stumped experts. Some say bad
vaccines may have “masked” the disease, resulting in healthy
looking chickens…which carry the virus and pass it around.

Lo urged cutting poultry populations in problematic places
like China, which produces 14 billion chickens a year.

“For countries with huge human and poultry populations, the
answer is to reduce drastically the density of poultry … with
so many birds with no immunity at all or with partial immunity,
you are bound to get in trouble,” Lo said.