Hong Kong on high alert over bird flu outbreak

Concerns that an outbreak of what is suspected to be the deadly H5N1 bird flu virus in a wholesale market in Hong Kong, has prompted the culling of tens of thousands of chickens.

Government health authorities are taking immediate action in order to curtail the spread of the virus and is also considering the need to change the vaccine used to protect chickens against bird flu.

As Hong Kong health officials battle with the first outbreak in five years, experts are concerned that the virus might have mutated during the last six years but say it does not appear to have developed into a human-to-human, or more serious type of virus.

Health Secretary York Chow says because the virus has mutated Hong Kong and mainland researchers are exploring whether there is a need to replace the H5N2 vaccine with the H5N1 vaccine.

The vaccine currently in use, which was considered the most effective of its type during the last outbreak in 2003, is produced in the Netherlands and protects chickens against the H5 virus in general.

Experts suspect the virus which killed chickens this week at a farm in the New Territories area of Hong Kong, near the border with China, is the highly pathogenic H5N1 strain.

According to reports from Hong Kong 100 breeding and sentinel chickens died on Sunday at the poultry farm, where 60,000 chickens were being raised - sentinel chickens are deliberately left unvaccinated in order to provide early warning signs of viruses in the environment - Hong Kong has been using this method since 2003.

University of Hong Kong virologist Malik Peiris says while it remains unclear how the chickens became infected, it could have come from wild birds - such incidences are more common in winter.

It was in Hong Kong in 1997, where the world's first reported major H5N1 bird flu outbreak among humans occurred which killed six people and led to the culling of the entire chicken population of 1.5 million birds; the last outbreak on farms in 2003 led to the mass vaccination of chickens.

But now questions have been raised over the effectiveness of the vaccine used and there are worries it may be losing its potency as newer strains of the virus spread.

Experts say the outbreak could evolve into a crisis if the source of the virus is not located quickly.

Health Secretary Chow has placed Hong Kong on a 'serious alert' and announced a 21-day shutdown of the local poultry industry and suspended all live chicken imports from mainland China, which supplies many of the Hong Kong's live wholesale markets and another 80,000 birds from farms near centre of the outbreak will also be culled.

Though as yet there have been no reports of humans sickened by the virus, local farm workers have been quarantined and are undergoing health checks.

According to many experts Hong Kong is particularly vulnerable as it is close to China's Guangdong province, which has been the epicentre of many recent bird flu outbreaks.

Although the H5N1 bird flu remains essentially a disease which affects birds and is not easy for humans to catch, there has always been the prospect that the strain could mutate into a version which is easily spread among people - this could trigger a pandemic and kill millions - to date the H5N1 bird flu has infected 389 people since 2003, killing 246 of them.

Experts say by using genetic sequencing, scientists will be able to say within a week if there were changes or characteristics in the virus that may allow it to spread easily among people.