Urban Norway and black rats (Rattus norvegicus and Rattus rattus) are the source of a number of pathogens responsible for significant human morbidity and mortality in cities around the world. These pathogens include zoonotic bacteria (Leptospira interrogans, Yersina pestis, Rickettsia typhi, Bartonella spp., Streptobacillus moniliformis), viruses (Seoul hantavirus), and parasites (Angiostrongylus cantonensis). A more complete understanding of the ecology of these pathogens in people and rats is critical for determining the public health risks associated with urban rats and for developing strategies to monitor and mitigate those risks. Although the ecology of rat-associated zoonoses is complex, due to the multiple ways in which rats, people, pathogens, vectors, and the environment may interact, common determinants of human disease can still be identified. This review summarizes the ecology of zoonoses associated with urban rats with a view to identifying similarities, critical differences, and avenues for further study.

Wild animals not normally exposed to antimicrobial agents can acquire antimicrobial agent-resistant bacteria through contact with humans and domestic animals and through the environment. In this study we assessed the frequency of antimicrobial resistance in generic Escherichia coli isolates from wild small mammals (mice, voles, and shrews) and the effect of their habitat (farm or natural area) on antimicrobial resistance. Additionally, we compared the types and frequency of antimicrobial resistance in E. coli isolates from swine on the same farms from which wild small mammals were collected. Animals residing in the vicinity of farms were five times more likely to carry E. coli isolates with tetracycline resistance determinants than animals living in natural areas; resistance to tetracycline was also the most frequently observed resistance in isolates recovered from swine (83%). Our results suggest that E. coli isolates from wild small mammals living on farms have higher rates of resistance and are more frequently multiresistant than E. coli isolates from environments, such as natural areas, that are less impacted by human and agricultural activities. No Salmonella isolates were recovered from any of the wild small mammal feces. This study suggests that close proximity to food animal agriculture increases the likelihood that E. coli isolates from wild animals are resistant to some antimicrobials, possibly due to exposure to resistant E. coli isolates from livestock, to the resistance genes of these isolates, or to antimicrobials through contact with animal feed.

Background Leptospira interrogans is a bacterial zoonosis with a worldwide distribution for which rats (Rattus spp.) are the primary reservoir in urban settings. In order to assess, monitor, and mitigate the risk to humans, it is important to understand the ecology of this pathogen in rats. The objective of this study was to characterize the ecology of L. interrogans in Norway rats (Rattus norvegicus) in an impoverished inner-city neighborhood of Vancouver, Canada.Methodology/Principal FindingsTrapping was performed in 43 city blocks, and one location within the adjacent port, over a 12 month period. Kidney samples were tested for the presence of L. interrogans using PCR and sequencing. A multivariable model was built to predict L. interrogans infection status in individual rats using season and morphometric data (e.g., weight, sex, maturity, condition, etc.) as independent variables. Spatial analysis was undertaken to identify clusters of high and low L. interrogans prevalence. The prevalence of L. interrogans varied remarkably among blocks (0–66.7%), and spatial clusters of both high and low L. interrogans prevalence were identified. In the final cluster-controlled model, characteristics associated with L. interrogans-infection in rats included weight (OR = 1.14, 95% CI = 1.07–1.20), increased internal fat (OR = 2.12, 95% CI = 1.06–4.25), and number of bite wounds (OR = 1.20, 95% CI = 0.96–1.49).Conclusions/SignificanceBecause L. interrogans prevalence varied with weight, body fat, and bite wounds, this study suggests that social structure and interactions among rats may influence transmission. The prevalence and distribution of L. interrogans in rats was also highly variable even over a short geographic distance. These factors should be considered in future risk management efforts.

Widespread circulation of SARS-CoV-2 in humans raises the theoretical risk of reverse zoonosis events with wildlife, reintroductions of SARS-CoV-2 into permissive nondomesticated animals. Here we report that North American deer mice (Peromyscus maniculatus) are susceptible to SARS-CoV-2 infection following intranasal exposure to a human isolate, resulting in viral replication in the upper and lower respiratory tract with little or no signs of disease. Further, shed infectious virus is detectable in nasal washes, oropharyngeal and rectal swabs, and viral RNA is detectable in feces and occasionally urine. We further show that deer mice are capable of transmitting SARS-CoV-2 to naïve deer mice through direct contact. The extent to which these observations may translate to wild deer mouse populations remains unclear, and the risk of reverse zoonosis and/or the potential for the establishment of Peromyscus rodents as a North American reservoir for SARS-CoV-2 remains unknown.

Norway and black rats (Rattus norvegicus and Rattus rattus) are among the most ubiquitous urban wildlife species and are the source of a number of zoonotic diseases responsible for significant human morbidity and mortality in cities around the world. Rodent ecology is a primary determinant of the dynamics of zoonotic pathogens in rodent populations and the risk of pathogen transmission to people, yet many studies of rat-associated zoonoses do not account for the ecological characteristics of urban rat populations. This hinders the development of an in-depth understanding of the ecology of rat-associated zoonoses, limits comparability among studies, and can lead to erroneous conclusions. We conducted a year-long trapping-removal study to describe the ecological characteristics of urban rat populations in an inner-city neighborhood of Vancouver, Canada. The study focused on factors that might influence the ecology of zoonotic pathogens in these populations and/or our understanding of that ecology. We found that rat population density varied remarkably over short geographical distances, which could explain observed spatial distributions of rat-associated zoonoses and have implications for sampling and data analysis during research and surveillance. Season appeared to influence rat population composition even within the urban environment, which could cause temporal variation in pathogen prevalence. Body mass and bite wounds, which are often used in epidemiologic analyses as simple proxies for age and aggression, were shown to be more complex than previously thought. Finally, we found that factors associated with trapping can determine the size and composition of sampled rat population, and thus influence inferences made about the source population. These findings may help guide future studies of rats and rat-associated zoonoses.