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.

In the case of critically endangered California condors, scientists organized a vaccination program -- including in San Diego -- after some birds became infected; however, that’s not a realistic option for most wild bird species.

The H7N9 strain of bird flu was detected on a poultry farm in Mississippi. The infection of 47,654 commercial chickens was confirmed on March 13 by the World Organization for Animal Health.