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Avian Influenza Moves into Zoos and Wildlife

New findings extend the host range of the avian influenza A (H5N1) virus to tigers and leopards.

Avian influenza H5N1 has caused more than 30 human and 100 million bird deaths in Southeast Asia. Researchers recently investigated the unexpected deaths of two tigers and two leopards at a zoo in Suphanburi, Thailand, in December 2003, during an avian influenza outbreak occurring nearby.

Necropsy of the animals revealed pulmonary consolidation and multifocal hemorrhage in many organs; one leopard and one tiger showed evidence of encephalitis. Lung samples from all four animals tested positive by PCR for H5N1. Immunohistochemical examination of tissue showed that alveolar and bronchiolar epithelial cells expressed influenza virus antigen. Influenza A virus isolated from lung samples was sequenced. Phylogenic analysis showed the virus to be virtually identical to the H5N1 found in poultry; it had not reassorted with mammalian influenza viruses before infecting the felids. Prior to becoming sick, the zoo animals had been fed fresh chicken carcasses from a local slaughterhouse. They had been vaccinated against feline panleukopenia 2 weeks before dying; three animals tested positive for this virus at necropsy but had no lesions suggesting its presence.

Comment: These findings document that the host range of the H5N1 virus extends to nondomestic cats. Other recent investigations have shown that domestic cats can be infected and can transmit infection horizontally (see Journal Watch Infectious Diseases Nov 5 2004). The zoo animals presumably became infected by eating uncooked, infected birds. The authors raise the possibility that the live feline panleukopenia virus vaccine could have had an immunosuppressive effect, but no findings supported infection with this virus as a primary cause of death. And now more than 100 Bengal tigers have died at a zoo near Bangkok after eating raw meat from chickens apparently infected with the H5N1 virus.

— Mary E. Wilson, MD

Published in Journal Watch Infectious Diseases December 10, 2004

Citation(s):

Keawcharoen J et al. Avian influenza H5N1 in tigers and leopards. Emerg Infect Dis 2004 Dec; 10:2189-91.

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