German health officials slaughtered 160,000 geese over the weekend after the deadly H5N1 bird-flu virus was found in a poultry farm near the southern city of Erlangen, according to dpa. The cull was ordered after 400 geese were found dead in their compound on Friday. Tests by the Friedrich Loeffler Institute of Veterinary Medicine found the lethal strain in five of the birds. A team of eight vets and poultry workers at the farm in Wachenroth, Bavaria, started what officials called the biggest ever culling operation in Germany late on Saturday. The birds were placed in three large containers where they were either gassed or electrocuted, officials said after the operation ended on Sunday afternoon. A three-kilometre exclusion zone was set up around the farm as officials began tracking down the cause of the infection. Initial reports said the infected animals came from another poultry farm in the northern state of Lower Saxony, but this was later denied. "We have not been able to pinpoint the source of outbreak," said Bavarian Health Secretary Otmar Bernhard. "The infection might have come frow straw, but that is just a suspicion." The H5N1 strain of avian influenza has killed nearly 200 people in recent years, mainly through direct contact with poultry. Most of the victims have been in Asia. There have been no human deaths from bird flu in Europe, where outbreaks were reported recently in several countries, including Germany and the Czech Republic. Bird flu hit wild water-birds and some domestic poultry in other parts of Germany this year.