Clinical signs and results of specific diagnostic testing among captive birds housed at zoological institutions and infected with West Nile virus

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Abstract
During 2002, West Nile virus (WNV) infection was diagnosed in 11 birds housed in outdoor exhibits at 5 zoological institutions in Kansas. Eight birds were examined because of neurologic abnormalities; 2 died suddenly without any clinical signs of disease. Results of CBCs and serum biochemical testing were nonspecific. Results of a plaque reduction neutralization test to detect circulating antibodies against WNV were positive for 2 of 8 birds. Results of a reverse transcriptase-polymerase chain reaction assay of an oral cavity swab specimen for WNV RNA were positive for 4 of 5 birds. One bird survived; the remaining 10 died or were euthanatized, with 9 of the 10 dying or being euthanatized within 3 days of the onset of clinical signs. In all 10 birds that died or were euthanatized, WNV infection was confirmed on postmortem examination by means of specific testing. Findings in these birds suggest that West Nile virus infection can be difficult to diagnose antemortem because clinical signs mimic those associated with other more common avian diseases. Neither of the antemortem diagnostic tests was definitive for diagnosing WNV infection in these cases.