Spatial variation in the parasite communities and genomic structure of urban rats in New York City

Abstract

Brown rats (Rattus norvegicus) are a globally distributed pest. Urban habitats can support large infestations of rats, posing a potential risk to public health from the parasites and pathogens they carry. Despite the potential influence of rodent-borne zoonotic diseases on human health, it is unclear how urban habitats affect the structure and transmission dynamics of ectoparasite and microbial communities (all referred to as "parasites" hereafter) among rat colonies. In this study, we use ecological data on parasites and genomic sequencing of their rat hosts to examine associations between spatial proximity, genetic relatedness and the parasite communities associated with 133 rats at five sites in sections of New York City with persistent rat infestations. We build on previous work showing that rats in New York carry a wide variety of parasites and report that these communities differ significantly among sites, even across small geographical distances. Ectoparasite community similarity was positively associated with geographical proximity; however, there was no general association between distance and microbial communities of rats. Sites with greater overall parasite diversity also had rats with greater infection levels and parasite species richness. Parasite community similarity among sites was not linked to genetic relatedness of rats, suggesting that these communities are not associated with genetic similarity among host individuals or host dispersal among sites. Discriminant analysis identified site-specific associations of several parasite species, suggesting that the presence of some species within parasite communities may allow researchers to determine the sites of origin for newly sampled rats. The results of our study help clarify the roles that colony structure and geographical proximity play in determining the ecology of R. norvegicus as a significant urban reservoir of zoonotic diseases. Our study also highlights the spatial variation present in urban rat parasite communities, indicating that rats across New York City are not reservoirs for a homogenous set of parasites and pathogens. As a result, the epidemiological risks may be similarly heterogeneous for people in urban habitats.

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

“…Interestingly, limited movement was supported by an analysis of the ectoparasite communities of urban Norway rats. In this study, Angley et al (2018) found that rats located near each other geographically had more similar assemblages of ectoparasites than did rats located further apart. Because rat ectoparasites are transmitted among individuals via close contact, this implied that rats near each other came into contact with each other more frequently than those further apart.…”

“…Although such extended movements are infrequent [e.g., 19 of 230 black rats (8.2%) were classified as migrants in Sahel Niger (Berthier et al, 2016)], evidence of gene flow among Norway rat colonies from 1.5 to 3 km apart suggests that connectivity among populations is maintained by immigration amongst colonies (Gardner-Santana et al, 2009;Combs et al, 2018a). This dispersal may be nonrandom, whereby individuals move among similar habitat types (e.g., residential areas vs. mixed-used; Angley et al, 2018) and may also be facilitated anthropogenically, such as by commercial transport along road networks (Berthier et al, 2016).…”

Significant Genetic Impacts Accompany an Urban Rat Control Campaign in Salvador, Brazil

“…It is possible that urban rats benefit from sharing colonies with closely related individuals (e.g., territory defense, stable social structure), and may avoid some inbreeding tradeoffs by having relatively accelerated reproductive life cycles. One benefit may be less diverse parasite and pathogen communities harbored by isolated rats, and dispersal and culling can disrupt these relatively insular colonies (Angley et al, 2018;Lee et al, 2018;Minter et al, 2019).…”

“…The current study is part of a multi-disciplinary effort to reduce the risk of leptospirosis for Pau da Lima residents, and a primary strategy is to reduce the population of Norway rats that serve as reservoirs of this bacterial pathogen (Ko et al, 1999;Costa et al, 2014;Richardson et al, 2017). Cities around the world are focused on reducing rat populations for reasons related to public health, quality of life, and protection of infrastructure (Bonnefoy et al, 2008;de Masi et al, 2009;Angley et al, 2018). The lethal control campaigns typically implemented are often successful at reducing the number of rats in the targeted areas yet are generally followed by a period of rapid population increase-the "boomerang effect" (Smith, 1963;de Masi et al, 2009).…”

Helminths of urban rats in developed countries: a systematic review to identify research gaps

“…Despite their close proximity with humans, the biology and ecology of urban rats have been understudied (Himsworth et al 2013 ). If bacterial and viral organisms carried by rats know nowadays an increasing scientific interest (particularly if they are zoonotic) (Himsworth et al 2013 ; Desvars-Larrive et al 2017 ; Angley et al 2018 ; Strand and Lundkvist 2019 ), studies on the helminth fauna of urban rats remain scarce. Helminths can modify wildlife host population dynamics (Hudson et al 1998 ; Albon et al 2002 ), communities (Mouritsen and Poulin 2002 ) and health status (Tompkins et al 2011 ).…”