New Chinese bird flu strain: low risk to Aust

Chinese scientists have traced the deaths of around 1500 migratory waterbirds, including geese, gulls and cormorants on isolated Qinghai Lake in western China to a new strain of the lethal H5N1 influenza virus , or 'bird flu'.

Researchers led by Dr H Chen, of the Joint Influenza Research Centre, found the first dead or dying bar-headed geese, black-headed and brown-headed gulls, and great cormorants on a single islet in the lake on April 30. Four days later, mortality rates had reached 100 birds a day, and the outbreak had spread to other islets.

The sick birds exhibited paralysis, unusual tilting of the head and a quivering neck, all symptoms of H5N1 infection in poultry.

The discovery, described in this week's edition of Nature, confirms the virus is circulating in migratory bird populations. Previously it had been isolated only from dead wild birds within flying distance of infected poultry farms in south-eastern China.

Veterinary and human health authorities had hoped that these birds were dead-end hosts for the virus, but the bar-headed goose, which accounted for 90 per cent of the mortality, is highly migratory.

When they analysed sequence data from the Qinghai Lake virus isolates, their coat-proteins (haemagglutinin and neuraminidase) differed subtly to isolates from infected poultry in urban markets in Fujian, Guandong, Hunan and Yunnan provinces in south-eastern China earlier this year, but the core matrix protein genes were very closely related.

However, the researchers found the new virus strain is easily distinguishable from strains that have caused recent human infections in Thailand and Vietnam. They concluded that the Qunghai Lake strain was probably a single introduction from domestic poultry in southern China earlier this year.

The lake is an important breeding site for bar-headed geese, which range widely through central Asia. The geese migrate south, over the Himalayas, into Myanmar (Burma).

The researchers concluded that, if the virus becomes established in bar-headed geese, it could be carried along the birds' winter migration routes, into densely populated regions of the south Asian subcontinent, which to date has been free of the virus, vastly expanding its geographic range.

That would require increased surveillance of poultry in the region, because it is virtually impossible to eliminate the virus once it establishes in poultry populations.

Dr Alan Hampson, director of the WHO Influenza Reference Laboratory in Parkville, Victoria, said it was possible that other migratory species that came into contact with the geese could carry it south-east to Australia, but the probability was very low.

Hampson said there was limited, sporadic monitoring of local and migratory waterbirds in Australia for influenza viruses that might be entering the country from south-east Asia. However, he believed it was unlikely the H5N1 strain would enter Australia by this route, and cause an outbreak in local poultry flocks or waterbirds.

"We work with groups at the Victorian Department of Primary Industry at Attwood and the University of Newcastle, and with the water study group of Birds Australia, when they have netting and banding sessions," Hampson said. "The Victorian department also monitors nomadic aquatic birds like ducks during the duck season, but it's necessarily ad hoc."

Hampson said the risk to the poultry industry was also low because most poultry were well housed, and after the major epidemic in NSW, which forced farmers to slaughter millions of birds, poultry farm dams were chlorinated to inactivate viruses.

"Biosecurity for the big producers is very high, but free-range poultry farms provide opportunities for poultry to come into contact with wild birds, so the risk can't be totally ignored," he said.

It had been impossible to establish the source of the big outbreak of 'bird flu in NSW, but the suspicion was that it the virus was presented in the water of an unchlorinated farm dam."