A fifth poultry farm near Melbourne has been infected with a highly pathogenic strain of bird flu. The farm is close to three others where an H7N3 strain of avian influenza had already spread and all 600 thousand chickens at the farms will be culled. Another farm in Victoria has had an outbreak of a different strain, neither is the same as the H5N1 type that has spread globally through bird and mammal populations and even into humans.