Virus Hitting Chicken Immunity May Be Cause Of Bird Flu - HONG KONG - A virus that weakens the immune system of chickens is likely to have set the stage for the rampant spread of bird flu across Asia, a Hong Kong scientist said Tuesday.

Frederick Leung, a zoology professor at the University of Hong Kong, said his studies conducted since 1996 showed that Hong Kong chickens hit by bird flu were usually struck by the infectious bursal disease virus about six months earlier.

Leung believes the IBDV probably also hit chicken farms across Asia that are currently suffering from bird flu, although he has no data about IBDV outside Hong Kong.

In 1996, an IBDV outbreak killed more than half of the chickens in farms that reported the disease, Leung said. About six months later, in 1997, Hong Kong suffered an outbreak of avian flu that killed six humans and led to the slaughter of 1.4 million chickens.

However, so far, no chicken farms in Hong Kong have reported bird flu in the current outbreak sweeping across Asia, and there has been no recent outbreak of IBDV here, Leung said.

Cambodia, Indonesia, Japan, Pakistan, South Korea, Taiwan, Thailand, Vietnam and Laos have reported cases of avian influenza. At least eight people have died of the disease in Thailand and Vietnam, most of them children.

IBDV, which causes diarrhea and sleepiness in chickens, occurs almost annually around the world. It normally kills fewer than 5% of infected chickens. But if the death rate jumps to 20%, bird flu is likely to follow, Leung said.

Vaccines against IBDV are only available for strains detected in North America and Europe, there isn't a vaccine for the strains found in Asia, Leung said.

"If we have vaccines against IBDV and good management in Asia, we can break the disease cycle and reduce the risk of bird flu," he said. It would take about six to eight months to produce IBDV vaccines, he said.

"The chickens should be fine if we are able to vaccinate them against both IBDV and H5N1 (bird flu)," he said, calling for regional cooperation.

The World Health Organization couldn't immediately be reached for comment on Leung's theory.

Separately, Hong Kong said in a statement Tuesday that it has temporarily halted poultry imports from Indonesia, Laos and Pakistan.

Hong Kong earlier imposed similar bans on Thailand and Cambodia.

Source: eFeedLink - 28th January 2004