Serological, reverse transcriptase-polymerase chain reaction, and immunohistochemical detection of West Nile virus in a clinically affected dog

Necropsy of an older dog submitted for evaluation of renal and central nervous system disease revealed histologic lesions compatible with West Nile viral encephalitis and myocarditis, as seen in other species. Using reverse transcriptase-polymerase chain reaction detection of envelope sequences, viral RNA was detected in most organs, and quantitative polymerase chain reaction revealed that at least 1,000 times more RNA was present in kidney than in brain, heart, spleen, or lung. Immunohistochemical evaluation of the kidney revealed intense staining of West Nile viral antigens in renal tubular epithelium and casts located within multifocal granulomatous interstitial inflammation. A canine immunoglobulin M (IgM)-capture enzyme-linked immunosorbent assay was developed, and patient serum was strongly positive for viral antibody. Retrospective and ongoing evaluation of sera from dogs with neurological disease and of those submitted for heartworm testing detected 4 dogs that were subclinically infected but without additional sickness. Judged by this experience, the kidney of West Nile virus-infected dogs may be an important target organ, one that might be suitable for antemortem biopsy. The presence of virus-specific IgM was demonstrated in the serum of this dog, and finding 4 positives among 169 additional canine sera received since late July 2002 suggests that seroconversion appears to be relatively uncommon in dogs during the outbreak in Missouri.