Rats About Town: A Systematic Review of Rat Movement in Urban Ecosystems

Norway and black rats (Rattus norvegicus and Rattus rattus) are ubiquitous urban pests, inhabiting cities worldwide. Despite their close association with people, urban rats remain difficult to control. This can be partly attributed to a general lack of information on basic rat ecology to inform management efforts. In this systematic review and narrative synthesis, we collate the published literature to provide a comprehensive description of what is known about urban rat movement, including information on home range, site fidelity, dispersal, movement patterns, barriers to, and factors impacting, movement. We also discuss the methodologies used to track and infer rat movement, as well as the advantages and limitations of employing these techniques. Our review suggests that the distances traveled by urban rats are location-specific, determined by both local resource availability and barriers to movement such as roadways. Although roads may impede rat movement, genetic techniques suggest that rats traverse roadways more often than revealed by capture-based tools, while long-distance dispersal events by either natural migration or facilitated by humans (i.e., as stowaways in transport vehicles) can maintain connectivity among distant populations. Because rat movement patterns are related to the transmission of rat-associated pathogens and the success of rodent control programs, these results have implications for city planners, pest control efforts, and public health. Therefore, we emphasize the importance of understanding local rat movement patterns in order to devise and deploy efficient and effective rat mitigation initiatives in urban centers

Tails of Two Cities: Age and Wounding Are Associated With Carriage of Leptospira interrogans by Norway Rats (Rattus norvegicus) in Ecologically Distinct Urban Environments

Leptospirosis is a zoonotic disease for which rats are the primary reservoir in urban environments. It is transmitted from rats to people via urine, and is responsible for significant human morbidity and mortality in under-resourced settings. To mitigate the risks posed to people, it is important to understand the ecology of the causative agent Leptospira interrogans. The overarching objective of this study was to compare L. interrogans carriage in urban Norway rats in two ecologically distinct urban environments. We trapped Norway rats (Rattus norvegicus) in Vancouver, Canada (N = 525) and Salvador, Brazil (N = 433) to evaluate whether rat characteristics (i.e., sex, weight, sexual maturity, pregnancy, and the presence of wounds) and location of capture were associated with L. interrogans status. Using generalized linear mixed models to control for clustering by trapping location, we found a greater prevalence of L. interrogans in Salvador (79%) than in Vancouver (12%), and greater spatial heterogeneity in pathogen prevalence in Vancouver than in Salvador. In both locations, we found that older rats and rats with more bite wounds had greater odds of L. interrogans carriage, although wounding influenced pathogen status more for younger animals. Additionally, we found that juvenile rats in Salvador were more likely to leave the nest infected with L. interrogans than were rats in Vancouver, suggesting that potential differences in early-life transmission dynamics exist between the two locations. Together, these results elucidate both general L. interrogans ecology, as well as the importance of geographical location in determining transmission among rats

Rat in a Cage: Trappability of Urban Norway Rats (Rattus norvegicus)

Understanding the local ecology of urban Norway rats (Rattus norevgicus) is necessary to inform effective rat mitigation strategies. While Capture-Mark-Recapture (CMR) methods can be used to acquire such ecological information (e.g., abundance, movement patterns, and habitat use), these techniques assume that all individuals of the study population are equally trappable. To test whether urban rats adhere to this assumption, we conducted a 4-week CMR study in an urban neighborhood of Vancouver, Canada, to evaluate whether rat characteristics (i.e., age, sex, size, wound status, and infection with the pathogen Leptospira spp.) were associated with trappability. We found that the majority of rats entered traps in the first 2 weeks of trapping, and that larger rats were caught earlier in the trapping period. However, smaller, sexually immature rats were recaught more often than were larger, sexually mature rats, suggesting that prior capture affects the ability to recapture urban Norway rats. This highlights the need for CMR studies to account for size, sexual maturity, and prior capture when interpreting data

Tails of Two Cities: Age and Wounding Are Associated With Carriage of Leptospira interrogans by Norway Rats (Rattus norvegicus) in Ecologically Distinct Urban Environments

Leptospirosis is a zoonotic disease for which rats are the primary reservoir in urban environments. It is transmitted from rats to people via urine, and is responsible for significant human morbidity and mortality in under-resourced settings. To mitigate the risks posed to people, it is important to understand the ecology of the causative agent Leptospira interrogans. The overarching objective of this study was to compare L. interrogans carriage in urban Norway rats in two ecologically distinct urban environments. We trapped Norway rats (Rattus norvegicus) in Vancouver, Canada (N = 525) and Salvador, Brazil (N = 433) to evaluate whether rat characteristics (i.e., sex, weight, sexual maturity, pregnancy, and the presence of wounds) and location of capture were associated with L. interrogans status. Using generalized linear mixed models to control for clustering by trapping location, we found a greater prevalence of L. interrogans in Salvador (79%) than in Vancouver (12%), and greater spatial heterogeneity in pathogen prevalence in Vancouver than in Salvador. In both locations, we found that older rats and rats with more bite wounds had greater odds of L. interrogans carriage, although wounding influenced pathogen status more for younger animals. Additionally, we found that juvenile rats in Salvador were more likely to leave the nest infected with L. interrogans than were rats in Vancouver, suggesting that potential differences in early-life transmission dynamics exist between the two locations. Together, these results elucidate both general L. interrogans ecology, as well as the importance of geographical location in determining transmission among rats

Global population divergence and admixture of the brown rat (Rattus norvegicus)

Native to China and Mongolia, the brown rat (Rattus norvegicus) now enjoys a worldwide distribution. While black rats and the house mouse tracked the regional development of human agricultural settlements, brown rats did not appear in Europe until the 1500s, suggesting their range expansion was a response to relatively recent increases in global trade. We inferred the global phylogeography of brown rats using 32 k SNPs, and detected 13 evolutionary clusters within five expansion routes. One cluster arose following a southward expansion into Southeast Asia. Three additional clusters arose from two independent eastward expansions: one expansion from Russia to the Aleutian Archipelago, and a second to western North America. Westward expansion resulted in the colonization of Europe from which subsequent rapid colonization of Africa, the Americas and Australasia occurred, and multiple evolutionary clusters were detected. An astonishing degree of fine-grained clustering between and within sampling sites underscored the extent to which urban heterogeneity shaped genetic structure of commensal rodents. Surprisingly, few individuals were recent migrants, suggesting that recruitment into established populations is limited. Understanding the global population structure of R. norvegicus offers novel perspectives on the forces driving the spread of zoonotic disease, and aids in development of rat eradication programmes

Development of cpn60-Based Real-Time Quantitative PCR Assays for the Detection of 14 Campylobacter Species and Application to Screening of Canine Fecal Samples▿ †

Campylobacter species are important organisms in both human and animal health. The identification of Campylobacter currently requires the growth of organisms from complex samples and biochemical identification. In many cases, the condition of the sample being tested and/or the fastidious nature of many Campylobacter species has limited the detection of campylobacters in a laboratory setting. To address this, we have designed a set of real-time quantitative PCR (qPCR) assays to detect and quantify 14 Campylobacter species, C. coli, C. concisus, C. curvus, C. fetus, C. gracilis, C. helveticus, C. hyointestinalis, C. jejuni, C. lari, C. mucosalis, C. rectus, C. showae, C. sputorum, and C. upsaliensis, directly from DNA extracted from feces. By use of a region of the cpn60 (also known as hsp60 or groEL) gene, which encodes the universally conserved 60-kDa chaperonin, species-specific assays were designed and validated. These assays were then employed to determine the prevalence of Campylobacter species in fecal samples from dogs. Fecal samples were found to contain detectable and quantifiable levels of C. fetus, C. gracilis, C. helveticus, C. jejuni, C. showae, and C. upsaliensis, with the majority of samples containing multiple Campylobacter species. This study represents the first report of C. fetus, C. gracilis, C. mucosalis, and C. showae detection in dogs and implicates dogs as a reservoir for these species. The qPCR assays described offer investigators a new tool to study many Campylobacter species in a culture-independent manner