The Characteristics of Wild Rat (Rattus spp.) Populations from an Inner-City Neighborhood with a Focus on Factors Critical to the Understanding of Rat-Associated Zoonoses

Abstract

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.

Indigenous house mice dominate small mammal communities in northern Afghan military bases

“…The results of previous research [33,34] as well as this study imply that rodent communities dominated by house mice may form spontaneously in sites like Camp Marmal due to the habitat structure and food sources introduced by the construction of the military bases. In contrast to this species, house mice are known to be carriers of other pathogens such as lymphocytic choriomeningitis virus, Leptospira spp., Rickettsia spp.…”

“…This setting therefore may select small mammal communities for commensals such as M. musculus due to both easy accesses in and out of the base but also offers easy access to food resources. In contrast to the patchy rodent population composition and density in an urban environment observed in Vancouver [33], the communities in Camp Marmal, PRT Kunduz and PRT Fayzabad showed a relatively similar composition concerning the dominance of house mice and occurrence of gray dwarf hamsters. This could be due to the modular and standardized design of makeshift military bases developed for missions such as ISAF.…”

“…Previous studies from Vancouver, Canada [33], and Buenos Aires, Argentina [34], have shown that urban small mammal communities are dominated by Rattus norvegicus, Rattus rattus or Mus musculus. A pivotal factor determining which of the three species dominates an urban environment is the structure and microenvironment provided by the specific location.…”

Studies of Sociosexual Interactions in Rats in an Externally Valid Procedure: Are They Relevant for Understanding Human Sexual Behavior?

“…A rough estimate based on the data provided in Davis, Emlen, & Stokes (1948) show that the density of wild rats is 0.02 rats per m2, which is much lower than that in the seminatural environment (1.25 rats per m2). Even though wild rat population density can vary remarkably even over short geographical distances, it does not reach the level of the seminatural environment (Himsworth, Jardine, Parsons, Feng, & Patrick, 2014). This means that even in a context with high population density, a group of rats rarely displays aggressive interactions.…”

The role of rodents in avian influenza outbreaks in poultry farms: a review

“…Therefore, effective hygiene measures such as reducing the availability of food sources and good habitat management can have a relatively large effect on a rodent problem. The density of a population of brown and black rats can be surprisingly heterogeneous when compared to the structure of the environment and availability of food sources (Himsworth et al 2014b). In a trapping study of brown and black rats in an inner city environment, the catch frequency over 43 contiguous city blocks was analysed compared to the urban functions of the trap locations.…”