Hong Kong Begins Mass Cull Of Birds At Marketplace

A government spokeswoman said some 3,000 chickens had been destroyed on Tuesday.

Health workers in masks culled tens of thousands of chickens in Hong Kong on Wednesday, a day after authorities raised the bird flu alert level to "serious" following a H5 bird flu outbreak at a farm.

The outbreak near the border with China was the city's first in five years despite mass vaccination of the birds, prompting concerns that the virus might have mutated.

"Viruses change and since 1997, it has been changing. If we have been using the same vaccine since 2003, its efficacy would not be the same," Ho Pak-leung, a microbiologist at the University of Hong Kong, told Reuters in an interview.

Laboratories in the city were trying to determine the precise identity of the H5 virus that caused the farm outbreak.

Another expert said it was likely to turn out to be the highly pathogenic H5N1 strain, which crops up regularly in flocks in Asia, parts of Europe and Africa.

Although H5N1 is mainly a disease among birds, it may mutate into a form that spreads easily among people. If that happens, it could trigger a pandemic and kill millions. Even in its current hard-to-catch form, H5N1 has infected 389 people since 2003, killing 246 of them.

Ho said scientists would be able to establish within a week if there were changes or characteristics in the virus that may allow it to spread easily among people.

"Genetic sequencing is being done. The key is whether it is still a fully avian virus," Ho said.

Scientists Hong Kong and mainland China are studying if new vaccines are needed to protect chickens against H5N1.

"If the study suggests that a new vaccine may provide better protection for chickens, we will select some to try out for a test trial of the new vaccine," Health Secretary York Chow said.

Workers clad in masks, white medical suits and black rubber gloves began the culling in a wholesale market on Wednesday. Culling also continued for the second day in areas within a 3 km radius of the infected farm.

By late afternoon, some 48,000 chickens had been killed, a government spokeswoman said, out of a total 80,000 birds that are meant to be culled.

China's southern Guangdong province has suspended all live poultry shipments to Hong Kong for 21 days to prevent any spread of the virus, China's official Xinhua news agency said, citing an official at the Guangdong Provincial Administration of Quality Supervision, Inspection and Quarantine.

Hong Kong told China that some 100 breeding and sentinel chickens died on Sunday at the Hong Kong poultry farm, where 60,000 chickens were being raised, the Xinhua report said.

Sentinel chickens are deliberately left unvaccinated for the purpose of providing early warning signs of viruses in the environment. Hong Kong has been using this method since 2003.