Bird flu hits migrating geese
China has reported its first outbreak of H5N1 bird flu since last year, when it seemed to have brought a widespread epidemic in poultry under control. This time, the virus has been found in wild geese in a nature reserve.
On 4 May, 178 bar-headed geese that had just completed their arduous annual migration over the Himalayas from northern India were found dead at Qinghai Lake Nature Reserve in western China. After initial denials, the Chinese agriculture ministry announced this week that the birds died of H5N1, and that the same fate had also befallen 340 gulls, cormorants and ducks in the reserve. China is vaccinating all poultry in the region, and has closed nature reserves to the public.
Scientists consider it unlikely that the geese carried H5N1 into China, though this cannot be ruled out. Rather, the deaths could show that H5N1 is continuing to circulate in China, despite the mass vaccination of poultry. One of the hazards of vaccination is that unless there is stringent monitoring it can allow the virus to persist silently while suppressing visible outbreaks. This could mean that H5N1 remains widespread in Chinese poultry, despite the lack of reported cases.
"We can't be sure until we see the genetic sequence, but it is not unlikely that these cases are spillback from local poultry," says Albert Osterhaus, a leading flu expert at the University of Rotterdam in the Netherlands.
From issue 2501 of New Scientist magazine, 28 May 2005, page 7