Influenza virus is not known to affect wild felids. We demonstrate that avian influenza A (H5N1) virus caused severe pneumonia in tigers and leopards that fed on infected poultry carcasses. This finding extends the host range of influenza virus and has implications for influenza virus epidemiology and wildlife conservation.

During the second outbreak of avian influenza H5N1 in Thailand, probable horizontal transmission among tigers was demonstrated in the tiger zoo. Sequencing and phylogenetic analysis of those viruses showed no differences from the first isolate obtained in January 2004. This finding has implications for influenza virus epidemiology and pathogenicity in mammals.

A surveillance program for influenza A viruses (H5N1) was conducted in live bird and food markets in central Thailand during July 2006–August 2007. Twelve subtype H5N1 viruses were isolated. The subtype H5N1 viruses circulating in the markets were genetically related to those that circulated in Thailand during 2004–2005.