WEDNESDAY, July 6, 2005 (HealthDay News) -- A deadly strain of the avian flu has been found in wild geese in western China, raising the possibility that the birds could spread the virus far and wide when they migrate.
Although wild birds have contracted the virus before, they have not been known to actually transmit it.
It's unclear whether this development brings the possibility of a human pandemic of avian flu closer to reality.
"Maybe yes, maybe no," said Dr. Susan McLellan, an associate professor of medicine in the infectious diseases section at Tulane University's School of Medicine in New Orleans. "As other experts have pointed out, dead birds don't migrate very well."
"This incident may cause the expansion of the geographic distribution of this highly pathogenic H5N1 to those regions currently H5N1-free, such as India," added Dr. Yi Guan, senior author of a paper appearing in the July 6 online issue of Nature. "But I do not think that this development would take us one step closer to the human pandemic, at least not immediately. However, the opportunity seems to be increased."
Guan, an associate professor of microbiology at the University of Hong Kong, was the first person to detect SARS in civets from animal markets in 2004, thus helping to avert a new SARS outbreak.
Reports of the avian flu outbreak among wild birds appear this week, both in Nature and in Science, authored by two separate research teams.
Although this strain of avian flu, H5N1, has only infected a small number of humans, it has produced an inordinately high number of deaths. Should the virus undergo additional genetic changes, experts fear it could acquire the ability to jump from human to human with more ease, potentially leading to a global influenza outbreak similar to the one in 1918-19 that killed an estimated 40 million people.
Since the H5N1 virus first appeared in 2003, it has affected poultry farms in 10 Asian countries, including China, Thailand and Vietnam. At least 53 people have died of the virus, apparently becoming infected after close contact with poultry.
So far, wild birds that have tested positive for H5N1 were within flight range of infected poultry farms, suggesting the wild birds were "dead-end" hosts, having picked up the virus from the poultry but not transmitting it any farther.
But there are no poultry farms near Qinghai Lake, a protected nature reserve that is a breeding center for migratory birds from Southeast Asia, Siberia, Australia and New Zealand, the researchers reported.
Qinghai Lake is a sort of terminus for bar-headed geese and other migratory birds. They alight at the lake to breed in early April. Starting in September, they migrate south to Myanmar (formerly Burma) and over the Himalayas to India, and then return again to the lake the following year, the researchers said.
According to the Nature article, the virus was first detected on April 30, 2005, in bar-headed geese at the lake.
By May 4, about 100 birds a day were dying. By May 20, the virus had killed about 1,500 birds, mostly geese but also brown-headed gulls and great black-headed gulls, according to the Nature report.
Genetic sequencing revealed that the Qinghai virus did not exactly match the sequence for known H5N1 genomes (it has been characterized as genotype "Z"), and it also seemed to be more virulent in mice and chickens. This implies that the new samples had undergone some genetic "reassortment" and perhaps originated in wild birds, Guan said.
"The viruses found in the migratory birds at Qinghai Lake are different from those from Vietnam or Thailand," Guan said.
The authors of the Nature article said they felt it was unlikely that the outbreak would "burn itself out." They also pointed out that the virus could move to other migratory species, and then on to chickens and perhaps humans.
Farmers in Europe and the Indian subcontinent, they warned, should watch for signs of the disease.
What might happen beyond Qinghai Lake is an open question.
"This may not be too much of an issue," McLellan said. "There have been no [known] human infections connected to this outbreak. The question is where do you have the cross between wild animals and farm poultry. They need to keep the husbandry hygiene very, very good, and keep farm birds away from wild birds."
On Wednesday, United Nations health officials said it could take up to 10 years to rid Asia of the bird flu virus.
The researchers put forward a master plan to fight bird flu that includes educating backyard farmers and vaccinating poultry to prevent the disease from becoming a human pandemic, the Associated Press reported.
More information
The CDC has more on bird flu.
