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Title: Biologic characterization of chicken-derived H6N2 low pathogenic avian influenza viruses in chickens and ducks

Author
item JACKWOOD, MARK - University Of Georgia
item Suarez, David
item HILT, DEBORAH - University Of Georgia
item Pantin Jackwood, Mary
item WOOLCOCK, PETER - University Of California
item CARDONA, CAROL - University Of California

Submitted to: Avian Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/9/2009
Publication Date: 3/1/2010
Citation: Jackwood, M., Suarez, D.L., Hilt, D., Pantin Jackwood, M.J., Woolcock, P., Cardona, C. 2010. Biologic characterization of chicken-derived H6N2 low pathogenic avian influenza viruses in chickens and ducks. Avian Diseases. 54:120-125.

Interpretive Summary: Avian influenza continues to be a threat to commercial poultry as well as human health. Wild aquatic birds, including ducks, are the natural reservoirs of avian influenza viruses and play an important role in the ecology of the virus. Sometimes, avian influenza viruses transmit from wild aquatic to domestic birds producing subclinical infections, and occasionally, respiratory disease and drops in egg production. These viruses are named low pathogenicity avian influenza viruses (LPAI). In this study we biologically characterized H6N2 LPAI viruses by infecting chickens and ducks in order to compare adaptation of these viruses in these species. We examined the clinical signs, virus shedding, and immune response to infection in 4-week old white leghorn chickens, and 2-week old Pekin ducks. Virus shedding for all of the viruses was detected in the oral/pharyngeal swabs from chickens at 2 and 4 days after infection, but only 3 of the 5 viruses were detected at 7 days after infection. Only 2 viruses were detected in the cloacal swabs from the chickens. Virus shedding for 4 of the 5 viruses was detected in the oral/pharyngeal cavity of the ducks, and fecal shedding was detected for 3 of the viruses in ducks at 4 and 7 days after infection. All other fecal swabs from the ducks were negative. Compared to chickens, fewer ducks shed virus. Both the chickens and ducks developed antibodies against the virus. The data indicates that the H6N2 viruses can infect both chickens and ducks, but based on the number of birds shedding virus and lesions, the viruses appear to be more adapted to chickens.

Technical Abstract: In this study we biologically characterized H6N2 low pathogenicity avian influenza (LPAI) viruses by infecting chickens and ducks in order to compare adaptation of these viruses in these species. We examined the clinical signs, virus shedding, and immune response to infection in 4-week old white leghorn chickens, and 2-week old Pekin ducks. Five H6N2 viruses isolated between 2000 and 2004 from chickens in California and one H6N2 virus isolated from chickens in New York in 1989 were given intrachoanal at a dose of 1 X 106 embryo infectious dose50 per bird. Oral/pharyngeal and cloacal swabs were taken at 2, 4, and 7 days post-inoculation (PI) and tested by real-time reverse transcriptase-polymerase chain reaction for presence of virus. Serum was collected at 7, 14 and 21 days PI and examined for avian influenza virus antibodies by commercial ELISA test and hemagglutination inhibition (HI) test. Virus shedding for all of the viruses was detected in the oral/pharyngeal swabs from chickens at 2 and 4 days PI, but only 3 of the 5 viruses were detected at 7 days PI. Only 2 viruses were detected in the cloacal swabs from the chickens. Virus shedding for 4 of the 5 viruses was detected in the oral/pharyngeal cavity of the ducks, and fecal shedding was detected for 3 of the viruses (including the virus not shed by the oral/pharyngeal route) in ducks at 4 and 7 days PI. All other fecal swabs from the ducks were negative. Compared to chickens, fewer ducks shed virus. Both the chickens and ducks developed antibodies as evidenced by HI and ELISA titers. The data indicates that the H6N2 viruses can infect both chickens and ducks, but based on the number of birds shedding virus and histopathology, the viruses appear to be more adapted to chickens. Virus shedding, which could go unnoticed in the absence of clinical signs in commercial chickens, can lead to transmission of the virus among poultry. However the viruses isolated in 2004 did not appear to replicate or cause more disease than earlier virus isolates.