An avian influenza outbreak in Mexico initially reported as a low-pathogenic H7 subtype has now been classified as the highly pathogenic H7N3 subtype, according to a follow-up report submitted to the World Organisation for Animal Health.

The strain is responsible for 211,424 bird deaths at three large commercial farms in the Mexican state of Jalisco, and is the first highly pathogenic bird flu outbreak since the mid-1990s, say Mexican veterinary authorities. More than 1 million birds are susceptible, and 587,160 have been sickened. Roughly 60,000 birds have been culled so far in an effort to halt the virus while sampling takes place at 60 poultry farms near the infected area. Quarantine measures are also in place to prevent the virus from spreading.