Vector-borne Viruses in Ungulates in Ontario, Canada: Distribution and Risk of Orbivirus Establishment

The purpose of this thesis was to investigate the potential risk posed by vector-borne pathogens to Ontario’s wildlife and livestock populations, in particular, epizootic hemorrhagic disease viruses (EHDV) and bluetongue viruses (BTV). Ontario lacks information describing the prevalence and distribution of certain vectors and pathogens despite the imminent threat vector-borne pathogens may pose to wildlife and livestock populations with their northward spread facilitated by changing climatic conditions. A retrospective analysis was performed using post-mortem findings and diagnoses for wild cervids from Ontario and Nunavut over a 27-year period to provide a long-term outlook of detected diseases and potential health threats. The most common causes of morbidity and mortality were noninfectious. Deaths attributed to infectious diseases were most often bacterial in origin. Viral vector-borne pathogens were rarely documented. We documented the first cases of EHDV (serotype 2) in free-ranging white-tailed deer in southern Ontario in 2017. Then, we sought to characterize Culicoides vector abundance and distribution, as well as assess transmission of EHDV and BTV in livestock, and BTV, EHDV, West Nile virus (WNV), eastern equine encephalitis virus (EEEV), Powassan virus (POWV) and heartland virus from free-ranging and captive cervids across Ontario for two consecutive field seasons. From June-October of 2017-2018 LED light suction traps were placed on farms and in natural areas across southern Ontario, and all Culicoides vectors collected were taxonomically identified. A total of 33,905 Culicoides spp. were collected, encompassing 14 species from seven subgenera and one species group. Culicoides sonorensis, a known vector of EHDV and BTV, was collected both years. Additionally, C. kibunensis and C. baueri were collected both years and these represent new records for Ontario, with C. baueri representing a new species record for Canada. Blood samples from 349 livestock and 217 cervids were collected from 2016 to 2019. Fifteen (9.0%) cattle were seropositive for EHDV-serotype 2. Nine (4.2%) cervids were seropositive for flaviviruses; three were confirmed as WNV, three as EEEV, and one as POWV. Collectively, these results on vector and arthropod-borne virus abundance and distribution will contribute to the development of management strategies for safeguarding Ontario livestock and wildlife populations.