Factors affecting the occurrence and distribution of canine distemper virus in raccoons (Procyon lotor) in Ontario, Canada

Canine distemper virus (CDV) is one of the most common infectious causes of mortality in wild carnivores, particularly raccoons (Procyon lotor). Our objectives were to describe the epidemiology of CDV in raccoons in southern... [ view full abstract ]

Canine distemper virus (CDV) is one of the most common infectious causes of mortality in wild carnivores, particularly raccoons (Procyon lotor). Our objectives were to describe the epidemiology of CDV in raccoons in southern Ontario and determine how seasonal, demographic, and spatial factors affect its occurrence and distribution. Between January 2014 and February 2015, pooled lung and lymph node samples from 366 raccoons submitted to the Canadian Wildlife Health Cooperative were tested for CDV using real-time PCR. Logistic regression was used to identify associations between CDV and explanatory variables (age, sex, season, reason for submission, and location). CDV was detected in 41% of samples submitted. In the multivariable model, raccoons submitted in the winter were significantly more likely to test positive than those submitted in the spring, summer or fall and adults were more likely to test positive than juveniles. Raccoons exhibiting unusual behavior were significantly more likely to test positive than those that appeared normal prior to submission. However, 27% of raccoons that appeared normal tested positive for CDV. The results suggest that CDV infection in raccoons may be subclinical; however, results may be affected by the subjective nature of distinguishing abnormal from normal behavior, or they may reflect differences in clinical manifestation and detectability at different stages of infection (e.g., early stages or recovery). If a significant proportion of raccoons infected with CDV are truly subclinical, this would have important implications for the spread of the virus in wildlife populations. Further work comparing PCR results to necropsy findings is underway.