(Agencies)
Updated: 2004-02-09 11:17

Up to 70 percent of people who have contracted bird flu in the latest Asian outbreak have died from the virus, making it twice as deadly as the last outbreak in 1997, a Hong Kong doctor said Sunday.

Eighteen people have died so far -- 13 in Viet Nam and five in Thailand -- and the virus has been reported in 11 countries.

China confirmed the deadly H5N1 strain of bird flu had been detected in a further six provinces Sunday, while Japan banned chicken imports from the United States after a milder strain of bird flu was discovered in Delaware.

"The data suggests it (mortality rate) is in the range of 60 to 70 percent, so we are quite shocked by this," David Hui, a specialist in respiratory medicine at the Chinese University of Hong Kong, told Reuters Television. "Last time (in 1997), the mortality rate was 30 percent."

Hui said there was little evidence that the virus was being spread by anything other than contact with sick poultry, but it was unclear why the H5N1 strain was this time more lethal or why only two countries had reported human deaths.

"This is a puzzle...we are trying to find out: Is the virus changing in structure? Is it becoming more virulent? Is the clinical spectrum different from 1997?" he said.

Hui is one of four experts from Hong Kong who arrived in Vietnam Sunday to join World Health Organization (WHO) efforts to contain the bird flu outbreak.

Health experts fear the bird flu virus could combine with a human form and mutate into a contagious disease for which people have no resistance.

TRANSPORT BAN AND CULL ORDERED

The virus has struck virtually all of Viet Nam's 64 provinces and major cities. Hanoi has ordered a nationwide ban on the transport of poultry and a cull of all fowl in the capital.

China confirmed outbreaks in six provinces -- Hubei, Shaanxi, Gansu, Hunan, Guangdong and Zhejiang -- previously suspected of harbouring the H5N1 strain, China Central Television (CCTV) reported Sunday.

Thirteen of China's 31 provinces have confirmed or suspected outbreaks of avian influenza. Chinese TV said there had been no reports of human infections.

Hong Kong saw a similar H5N1 strain of bird flu in 1997, which killed six people. A cull of the territory's entire 1.5 million poultry population in three days is credited with stopping the virus in its tracks.

As well as H5N1, milder strains of the virus have been detected, such as H7 found this weekend in the United States.

Japan's Agriculture Ministry said Sunday it was trying to confirm the nature of the U.S. virus, which led to the slaughter of 12,000 birds at a farm in Delaware Saturday.

Japan has largely escaped the effects of the virus which has wreaked havoc on Asia's poultry industry. Singapore and Malaysia said they also had suspended imports of US chicken, while Hong Kong stopped imports from Delaware.

Hui said he was surprised by the report of bird flu in the United States, adding authorities did the right thing to cull the infected birds.

Tens of millions of poultry in Asia have been killed by the virus or culled.