The Hindu : Opinion / News Analysis : To contain the spread of bird flu virus

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Thursday, Jul 07, 2005

Opinion

Opinion - News Analysis

To contain the spread of bird flu virus

N. Gopal Raj

Widespread incidence of the H5N1 bird flu virus infection among migratory birds at a lake in western China has sparked concern.

TWO PAPERS appearing in the prestigious scientific journals Nature and Science say that the infection of large numbers of migratory waterfowl congregated at a lake in western China could lead to the deadly H5N1 bird flu virus spreading beyond the countries in south-east and east Asia where it is currently prevalent.

The H5N1 bird flu virus is lethal to both poultry and humans. Millions of birds have died or been slaughtered as a result of the ongoing H5N1 epidemic. Since December 2003, over 100 people in Vietnam, Thailand, and Cambodia have been infected with the H5N1 virus and half of them have died. Experts fear that if the virus develops the ability to spread easily from human to human, it could set off an influenza pandemic.

The H5N1 viral infection among migratory birds at Lake Qinghai in western China was first noticed in early May this year. By the end of the month, the outbreak had spread and some 1,500 birds were dead.

After sequencing the genes of the H5N1 viruses found in birds, influenza virus specialists in China and the United States say in their Nature paper that the infection at the lake appeared to have happened as a result of a "a single introduction, most probably from poultry in southern China."

"Our findings indicate that H5N1 viruses are now being transmitted between migratory birds at the lake," said the authors of the Nature paper. The large bird population at the lake made it unlikely that the outbreak would burn itself out and the virus could move to other migratory species that could then act as carriers, remaining highly pathogenic for domestic chickens and possibly humans too.

Some 90 per cent of the dead birds were bar-headed geese (Anser indicus) and the current H5N1 virus could become established in these geese. "There is a danger that [the virus] might be carried along the birds' winter migration routes to densely populated areas in the south Asian subcontinent, a region that seems free of this virus, and spread along migratory flyways linked to Europe," according to the Nature paper.

Apart from the bar-headed geese, the brown-headed gulls (Larus brunnicephalus) and great black-headed gulls (Larus ichthyaetus) were the other two species of migratory birds killed by the H5N1 virus at lake, say the scientists.

In their Science paper, Chinese scientists report that the H5N1 virus isolated from a bar-headed goose, when tested on chickens and mice, proved more virulent than H5N1 strains isolated previously from ducks in China. They speculated that this more lethal strain had originated in birds that came from south-east Asia.

Breeding centre

Observing that the lake was a breeding centre for birds from south-east Asia, Siberia, Australia, New Zealand, Tibet and India, the Chinese scientists said in their Science paper that the H5N1 infection in migrant waterfowl indicated that the virus had the potential to become a global threat.

But Indian conservationists say that fears of the H5N1 virus being brought to India by migratory birds appear to be overblown.

"I am worried that reports of migratory birds carrying the H5N1 virus could lead to the indiscriminate slaughter of these birds," remarks Ranjit Daniels, a Chennai-based biodiversity specialist. Even if the same species of migratory birds were found both in India and China, the two populations could be following different migratory routes and therefore not intermingle.

The bar-headed goose found in India breeds in Ladakh and migrates south during winter, says V.S Vijayan, an experienced ornithologist who established the Salim Ali Centre for Ornithology and Natural History at Coimbatore. Likewise, studies of migratory birds tagged with rings showed that the Indian populations of brown-headed gulls and great black-headed gulls too breed in the Himalayan regions and then travel south in the winter, he told The Hindu.

The Qinghai outbreak showed that wildlife could play an important role in the dissemination of the disease, commented the Food and Agriculture Organisation. It has advised against killing of wild birds, calling instead for strict surveillance and prevention measures.

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