Thousands of wild birds in north-west China may have been infected by a bird flu virus closely related to the one that has devastated poultry farms in south-east Asia. The birds might carry the virus as far as India, Australia and Europe. That is the warning from two teams of scientists in China. They report in Nature and Science this week that a massive die-off of birds at Qinghai Lake in north-west China, a major summering spot for migratory waterfowl, is due to H5N1.
Officially, 6000 birds had died by 1 July. But far more may have been affected, says George Gao, of the Chinese Academy of Sciences, and the leader of one of the teams. Tens of thousands of migrating water birds summer at the lake, says Taej Mundkur in Pune, India, an expert on the region’s birds with the international conservation group Wetlands International. In mid-August, the survivors will start returning to their winter ranges, which stretch from eastern Europe to Australia and Alaska, and overlap with the ranges of other migrants. Mundkur cautions that it is not known how many birds from Qinghai Lake migrate to the farthest reaches of their species’s known ranges. But if some birds carrying the virus remain healthy enough to migrate, the disease could spread far and wide.
So far no testing has been done to see if this is likely. “We have had no chance to sample healthy migratory birds by Qinghai Lake,” says Yi Guan at Shantou University Medical College in Guangdong province, who led the other team. The Chinese ministry of agriculture is reportedly planning to investigate later in July, but neither Gao nor Guan has received permission to study healthy birds. The RNA sequence of the Qinghai virus reveals that three of its eight genes are almost identical to those of a virus isolated from a chicken in Shantou in 2003. The other five genes resemble those of viruses found in southern China earlier in 2005, which belong to the “Z genotype” virus circulating across east Asia.
This means the Qinghai virus was not, as first claimed by officials, brought into China from other countries by migrating birds. The bird that started the outbreak might have picked up the virus in southern China or from poultry closer to Qinghai, say Guan and Gao. What is not clear is whether the Qinghai virus is any more deadly to wild birds than the other H5N1 variants that have killed wild birds. The Qinghai outbreak might merely be the first time that H5N1 has had the opportunity to infect such a large number of wild fowl. “Any susceptible migrant could pick up the virus and die in the wild without being noticed,” says Mundkur. “It is only because the birds were congregating in a place that is visited, that the mass die-off was reported at Qinghai.” Nor is it known if the Qinghai virus could kill humans. It does have a mutation associated with increased deadliness in mammals – Gao found that it kills all mice infected with it in four days – but this mutation may not be enough to make the virus dangerous for humans.
What is certain is that if the virus spreads to other countries, it will decimate poultry industries. The sequence also shows that H5N1 viruses in Asia are swapping genes – which could give rise to a virus capable of causing a human pandemic.
August 2, 2005
Original web page at New Scientist