Host Disease and Environmental Factors Associated with Zoonotic Pathogens in Urban Norway Rats (Rattus norvegicus)
The purpose of this research was to investigate the role of environmental and intra-host factors in the epidemiology and ecology of zoonotic pathogen carriage by urban Norway rats (Rattus norvegicus). Rats are the hosts of many zoonotic pathogens, including Yersinia pestis and Leptospira interrogans, the causative agents of plague and leptospirosis, respectively. Knowledge of the ecology and epidemiology of zoonotic pathogens in their rat hosts is important for understanding and mitigating the risk to people. Most studies of rat-associated zoonotic pathogens investigate rat demographic characteristics. But many factors across hierarchical levels of biological organization can influence pathogens in hosts. These include environmental and intra-host factors such as co-infections and disease. Using samples and data collected during a year-long trap and removal study of rats set in Vancouver, British Columbia, I first assessed microenvironmental features, time-lagged weather variables and rat abundance for associations with four potentially zoonotic pathogens carried by rats (Bartonella tribocorum, Clostridium difficile, antimicrobial resistant Escherichia coli and methicillin-resistant Staphylococcus aureus). Significant factors included temperature, precipitation, specific land use and pavement condition. No pathogens were associated with rat abundance. These results may inform predictive modeling, targeted surveillance activities and specific interventions. Next, I used pathological analyses to document the spectrum of macroscopic and microscopic disease found in these rats. The most severe and frequent lesions were infectious and inflammatory. Finally, I assessed the most common lesions and parasite infections for associations with three zoonotic pathogens (B. tribocorum, C. difficile and L. interrogans). Parasite infections were associated with B. tribocorum, while C. difficile and L. interrogans were associated with specific lesions, and rats were rarely co-infected with multiple zoonotic pathogens. The impact of the environment, weather, lesions and parasitic infections varied depending on the zoonotic pathogen. Collectively, these results suggest a possible dynamic interplay among these factors, adding to the growing knowledge of zoonotic pathogen ecology in rats. The disease ecology methods and concepts developed by this research are broadly applicable to the study of the epidemiology and ecology of zoonoses in other hosts and ecosystems.