The recent live bird market cases represent the second and third known cases of avian influenza in Philadelphia. In January, an infected wild bird was identified in West Philadelphia ’s Carroll Park section, and health officials notified the public because wild birds presented a greater risk for exposure.

Bird flu has been detected in a sheep in northern England, the first known case of its kind in the world, Britain's government said, adding to the growing list of mammals infected by the disease and fuelling fears of a pandemic.