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

Posted on: Tuesday, 25 April 2006, 00:10 CDT

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.

LESSONS TO LEARN

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.

Source: REUTERS

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