A Canine Distemper Outbreak in Alaska: Diagnosis and Strain Characterization Using Sequence Analysis

Vaccination with modified-live vaccines has been very effective in reducing the incidence of canine distemper, a disease that can be devastating in unvaccinated populations. A diagnostic submission to the Animal Health Diagnostic Laboratory at Michigan State University, East Lansing, Michigan, involved a case in which several hundred dogs in an Alaskan town died in a suspected canine distemper outbreak. Cytoplasmic and intranuclear eosinophilic inclusion bodies, consistent with canine distemper virus (CDV) infection, were found in urinary bladder, spleen, lung, and salivary gland. Direct fluorescent antibody test gave results that could be considered positive for canine distemper. Because of the condition of the tissues received, the histopathology and fluorescent antibody–staining results were suggestive but not conclusive of CDV. In this study, immunohistochemistry, reverse transcriptase–polymerase chain reaction (RT-PCR), and DNA sequencing were used to confirm the presence of canine distemper virus in these tissues and to perform molecular characterization of the virus. Immunohistochemistry showed the presence of the virus in spleen, lung, and salivary gland. Viral RNA was detected by RT-PCR in brain, spleen, liver, lung, and kidney, both with nucleoprotein and phosphoprotein (P)-gene–specific primers. Sequence alignment and phylogenetic analysis of a 540-bp P-gene fragment of the Alaskan strain with corresponding sequences of 2 vaccine and 7 wild-type CDV strains showed that the virus responsible for the outbreak was closely related to a virulent strain of distemper virus from Siberia.