China has reported only one outbreak since March 2004 – in July, in Anhui province. The authorities blamed this occurrence on wild waterfowl on a nearby lake.
But Albert Osterhaus, a leading flu expert at the University of Rotterdam in the Netherlands, told New Scientist that it is rare to find such highly pathogenic strains of bird flu in wild fowl. As for the geese in Qinghai, he says, “we can’t be sure until we see the genetic sequence, but it is not unlikely that these cases are spillback from local poultry”. The geese could have become infected by swimming in ponds used by infected local birds. In 2003, says Osterhaus, when Dutch poultry was hit by another highly pathogenic bird flu called H7, swans using the same pond as infected farm birds caught the H7 virus.
The geese could have carried the flu with them from India only if it did not make them ill at all. “We don’t know what H5N1 does in these geese,” says Osterhaus.
Richard Thomas of Bird Life International, a conservation organisation, says the stress of their migration, during which they reach altitudes over 10,000 metres, could in theory have caused the geese to fall ill on arrival with a virus that would previously not have affected them. But no reports of H5N1 have been confirmed in India, says Osterhaus. The exhausted birds would also have been easy prey for a flu virus they met in China, he adds.
June 7, 2005
Original web page at New Scientist