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 yesterday.
Frederick Leung, a zoology professor at the University of Hong Kong, said his studies conducted since 1996 showed that chickens here hit by bird flu were usually struck by the infectious bursal disease virus, (IBDV), about six months earlier.
Leung believes that IBDV probably also hit the chicken farms across Asia that were currently suffering from bird flu.
In 1996, an outbreak of IBDV killed over 50% of chickens in farms that reported they had 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.
No chicken farms here had reported bird flu so far, and there had been no recent outbreak of IBDV here, Leung said.
IBDV, which causes diarrhoea and sleepiness in chickens, occurs almost annually around the world. It normally kills less than 5% of infected chickens. But if the death rate jumps to 20%, bird flu was likely to follow, Leung said.
Vaccines against IBDV were only available for strains detected in North America and Europe; there was no 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,'' Leung said, adding that it will take about six to eight months to produce IBDV vaccines.
The chickens should be fine if we are able to vaccinate them against both IBDV and H5N1 (bird flu),'' he said, calling for regional co-operation in the matter. AP