A RETROSPECTIVE SUMMARY OF CERVID MORBIDITY AND MORTALITY IN ONTARIO AND NUNAVUT REGIONS OF CANADA (1991-2017).

Free-ranging cervids in Canada face diverse threats such as climate change, human population expansion, and the northward spread of vector-borne pathogens. However, we currently have a limited understanding of the impacts of these health challenges in Ontario cervids. Our objective was to identify and characterize causes of morbidity and mortality in free-ranging cervids submitted to the Ontario and Nunavut node of the Canadian Wildlife Health Cooperative (CWHC) over a 27-yr period (1991 to 2017). Submissions included carcasses submitted for full postmortem examination (gross and histopathology; n=196) and field-collected tissues (n=384). Ancillary tests were performed on a case-by-case basis. Univariable logistic regression was used to test for associations between select causes of morbidity and mortality, and factors such as sex, age, and season. Four cervid species were examined: white-tailed deer (Odocoileus virginianus; n=211), moose (Alces alces; n=140), elk (Cervus canadensis; n=136), and caribou (Rangifer tarandus caribou; n=93). Noninfectious disease was the most common general cause of morbidity and mortality (38.1%; 221/580) and was most commonly attributed to trauma (49.7%; 110/221). Deaths attributed to infectious diseases (34.3%; 199/580) were most often bacterial in etiology (45.7%; 91/199). The most common primary infectious disease diagnosed in caribou was digital limb infection, and moose were most commonly diagnosed with parasitic causes, including meningeal worm (Parelaphostrongylus tenuis) and winter tick (Dermacentor albipictus). Chronic wasting disease was not diagnosed among cervids tested during the study period, consistent with the previous lack of detection of the disease in Ontario. These results reveal that anthropogenic, infectious, and environmentally associated causes of morbidity and mortality are commonly diagnosed in cervids submitted to the CWHC Ontario and Nunavut regions, and represent potential population threats that should continue to be monitored.