Abstract

Wild waterfowl and shorebirds in the Delmarva Peninsula region within the Atlantic Flyway were sampled as part of the Early Detection of Highly Pathogenic H5N1 Avian Influenza (AI) in Wild Migratory Birds program. The United States Department of Agriculture (USDA) and state wildlife agencies submitted 7,858 samples for AI virus (AIV) testing by rRT-PCR to the University of Delaware Poultry Health System from April 2007 - March 2011. Virus isolation (VI) attempts were performed on samples with matrix gene cycle threshold (Ct) values {less than or equal to}33.9. Using rRT-PCR, AIV was detected in 14% (1091/7857) of the samples. In species with sample sizes >100, American black duck (28%), ruddy turnstone (27%), American green wing teal (21%), semipalmated sandpiper (27%), greater snow goose (12%), mallard (10%) and northern pintail (14%) showed the highest rates of AIV detection. Forty-four AIVs were recovered from eight species: American black duck, mallard, ruddy turnstone, American green-wing teal, greater snow goose, Canada goose, ring-necked duck, and mallard X American black duck. Recovered H5 (n=2) and H7 (n=2) viruses were found to be low pathogenicity by the USDA National Veterinary Services Laboratory. Additional AIVs represented a diversity of subtype combinations; H1-H4, H6, H10 and H11, and N subtypes N1-N4, and N6-N9. The rate of AIV recovery from swabbings was inversely related to cycle threshold value, ranging from 50% for Ct values of 16.0-18.9 to 5.1% for Ct values of 31-33.9.

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