Rat-Associated and Emerging Zoonotic Pathogens in Norway Rats (Rattus norvegicus) in Ontario, Canada: Surveillance, Epidemiology, and Ecology
Norway rats (Rattus norvegicus) thrive in close cohabitation with humans and carry a diversity of pathogens of public health and veterinary significance. This thesis was both an evaluation of zoonotic pathogen surveillance through partnerships with pest control professionals and an investigation of the ecology and epidemiology of rat-associated and emerging zoonotic pathogens in Norway rats. While zoonotic pathogen occurrence is well-documented in Norway rats in some regions, there are significant challenges associated with field studies of urban rats and a paucity of knowledge on the presence and ecology of these pathogens in Ontario. Based on a sample of rats collected by pest control professionals in Windsor, Ontario, I determined that pest control sourced carcasses were in adequate condition for the collection of a variety of tissue samples that could be used for surveillance of a range of pathogens. After establishing this as a feasible method of disease surveillance, I continued to collaborate with pest control professionals working in southern Ontario to investigate two emerging zoonotic pathogens: SARS-CoV-2 and hepatitis E virus (HEV) in Norway rats from southern Ontario. We did not detect SARS-CoV-2 RNA in any rats tested; 1.4% (2/138) were seropositive. Hepatitis E virus was detected in 5.6% (21/372) of rats. Phylogenetic analysis of partial ORF1-derived sequences indicated that all infections were Rocahepevirus ratti genotype C1 (rat HEV), which has been recently reported as the cause of multiple human cases of hepatitis E. Using regression analyses, I examined environmental and sociodemographic factors and their association with two rat-associated zoonotic pathogens (i.e., Leptospira interrogans and Bartonella spp.) in Norway rats from Windsor, Ontario. Leptospira interrogans and Bartonella spp. were detected in 12.7% (32/252) and 16.3% (37/227) of rats, respectively. I identified associations between infection status and environmental (i.e., building density, population density, and uncollected garbage) and sociodemographic factors (i.e., median household income and proportion of dwellings built in 1960 or before). This thesis adds to our current understanding of rat-associated and emerging zoonotic pathogen distribution and ecology in Norway rats.