( dpa ) - Pakistani authorities on Friday culled thousands of birds to control an outbreak of avian flu at poultry farms in the southern port city of Karachi, an official said.
"We have culled 5,500 birds after laboratory tests confirmed the presence of HH5N1 virus at a farm in Guddap district," said Ali Akbar, the director of Poultry Research Institute Sindh.
Animal health workers had tightened surveillance at hundreds of other farms that supply poultry products to the city's 15 million people, Ali said, adding the bird flu was limited to only one farm.
But some media reports recently suggested that the virus had affected several poultry farms. Tens of thousands of birds have died in the last three days and the dead foul are being illegally sold in the city, the daily Express said Thursday.
No human infections have yet been reported in Karachi but health officials were conducting tests of the poultry workers.
Pakistan's poultry population has seen multiple outbreaks of H5N1, the strain of avian influenza that can be deadly in humans, since 2006. The first human case was reported in 2007 when nine people in the North-West Frontier Province, six of them blood relatives, were confirmed to have contracted the virus in November.
However, the World Health Organization (WHO) later ruled out human-to-human transmission after retests of the patients' blood samples at its laboratory in Geneva.
Bird flu has killed at least 210 people worldwide since 2003. Most human cases of avian influenza are the result of contact with sick birds, but experts fear the virus might mutate into a form that spreads easily among humans, sparking a pandemic that could kill millions of people.