Pathogenicity of West Nile virus for turkeys

In the fall of 1993, West Nile virus (WNV) was isolated during an outbreak of neurologic disease in humans, horses, and wild and zoological birds in N ew York, Connecticut, and New Jersey. Turkeys could potentially be a large reservoir for WNV because of the high-density turkey farming and the presen ce of large wild turkey populations in the eastern seaboard of the United S tates. Little is known about the pathogenicity of WNV in domestic or wild t urkeys. Specific-pathogen-free S-wk-old turkeys were inoculated subcutaneou sly with 10(33) mean tissue culture infective doses of a WNV strain isolate d from the index case in a New York crow. No clinical signs were observed i n the turkeys over the 21 days of the experiment. One turkey died abruptly at 8 days postinoculation (DPI). Many turkeys developed viremia between 2 a nd 10 DPI, but the average level of virus was very low, less than needed to efficiently infect mosquitos. Low levels of WNV were detected in feces on 4 and 7 DPI, bur no virus was isolated from oropharyngeal swabs. WNV was no r transmitted from WNV-inoculated to contact-exposed turkeys. All WNV-inocu latcd poults seroconvert ed on 7 DPI. In the turkey that died, WNV was not isolated from intestine, myocardium, brain, kidney, or cloacal and orophary ngeal swabs, bur sparse viral antigen was demonstrated by immunohistochemis try in the heart and spleen. Turkeys in contact with WNV-inoculated turkeys and sham-inoculated controls lacked WNV specific antibodies, and WNV was n or isolated from plasma and cloacal and oropharyngeal swabs. These data sug gest that WNV lacks the potential to be a major new disease of turkeys and that turkeys will not be a significant amplifying host for infecting mosqui tos.