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Journal of Virology, April 2007, p. 4044-4051, Vol. 81, No. 8
0022-538X/07/$08.00+0     doi:10.1128/JVI.02346-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Emergence of Influenza A Virus Variants after Prolonged Shedding from Pheasants

Division of Virology, Department of Infectious Diseases,¹ Animal Resource Center, St. Jude Children's Research Hospital, Memphis, Tennessee 38105,³ Department of Biology, University of Memphis, Memphis, Tennessee 38152²

Received 26 October 2006/ Accepted 19 January 2007

We previously demonstrated the susceptibility of pheasants to infection with influenza A viruses of 15 hemagglutinin (HA) subtypes: 13/23 viruses tested were isolated for 14 days, all in the presence of serum-neutralizing antibodies; one virus (H10) was shed for 45 days postinfection. Here we confirmed that 20% of pheasants shed low-pathogenic influenza viruses for prolonged periods. We aimed to determine why the antibody response did not clear the virus in the usual 3 to 10 days, because pheasants serve as a long-term source of influenza viruses in poultry markets. We found evidence of virus replication and histological changes in the large intestine, bursa of Fabricius, and cecal tonsil. The virus isolated 41 days postinfection was antigenically distinct from the parental H10 virus, with corresponding changes in the HA and neuraminidase. Ten amino acid differences were found between the parental H10 and the pheasant H10 virus; four were in potential antigenic sites of the HA molecule. Prolonged shedding of virus by pheasants results from a complex interplay between the diversity of virus variants and the host response. It is often argued that vaccination pressure is a mechanism that contributes to the generation of antigenic-drift variants in poultry. This study provided evidence that drift variants can occur naturally in pheasants after prolonged shedding of virus, thus strengthening our argument for the removal of pheasants from live-bird retail markets.

Published ahead of print on 31 January 2007.