Amplification of pathogenicLeptospirainfection with greater abundance and co‐occurrence of rodent hosts across a counter‐urbanizing landscape

Abstract

Land use change can elevate disease risk by creating conditions beneficial to species that carry zoonotic pathogens. Observations of concordant global trends in increased pathogen prevalence or disease incidence and landscape change have generated concerns that urbanization could increase transmission risk of some pathogens. Yet host-pathogen relationships underlying transmission risk have not been well characterized within cities, even where contact between humans and species capable of transmitting pathogens of concern occurs. We addressed this deficit by testing the hypothesis that areas in cities experiencing greater population loss and infrastructure decline (i.e., counter-urbanization) can support a greater diversity of host species and a larger and more diverse pool of pathogens. We did so by characterizing pathogenic Leptospira infection relative to rodent host richness and abundance across a mosaic of abandonment in post-Katrina New Orleans (Louisiana, USA). We found that Leptospira infection loads were highest in areas that harboured increased rodent species richness (which ranged from one to four rodent species detected).Areas with greater host co-occurrence also harboured a greater abundance of hosts, including the host species most likely to carry high infection loads, indicating that Leptospira infection can be amplified by increases in overall and relative host abundance. Evidence of shared infection among rodent host species indicates that crossspecies transmission of Leptospira probably increases infection at sites with greater host richness. Additionally, evidence that rodent co-occurrence and abundance and Leptospira infection load parallel abandonment suggests that counter-urbanization can elevate zoonotic disease risk within cities, particularly in underserved communities that are burdened with disproportionate concentrations of derelict properties.

Rodent Virus Diversity and Differentiation across Post-Katrina New Orleans

“…The reverse was not found, suggesting that the potential for transmission is asymmetric. Consistent with this, signatures of directional transmission have been found for bacterial symbionts among co-occurring rodent host species [12,19]. We also detected several viruses in multiple host species, which is consistent with trends indicating that viruses exhibit less host specificity than bacterial symbionts [31].…”

“…For example, targeted assays of known rodent-associated bacterial and viral pathogens such as Bartonella [12,15], Rickettsia [15], Hantaviruses [15] and lymphocytic choriomeningitis virus (LCMV) [16,17] provide evidence of infection hotspots. Targeted assays of known pathogens like Leptospira also have demonstrated that infection prevalence can parallel external factors like physiography and host co-occurrence [11,[17][18][19]. Notably, exploratory surveys (e.g., unbiased metagenomic assays) have demonstrated that urban rodents can host more microbial and viral diversity than anticipated [20][21][22][23].…”

“…To gain further understanding of how disasters can influence the risk of pathogen transmission to humans, we undertook a metagenomic study of blood-borne viruses found in commensal rodents collected from across New Orleans (LA, USA) following Hurricane Katrina, which struck the city in late August 2005 [2,4,19]. We examined viral assemblages in populations of three cosmopolitan commensal species-Norway rats (Rattus norvegicus), roof rats (Rattus rattus), and house mice (Mus musculus)-from study areas that span a mosaic of habitat conditions that have arisen due to Katrina-related flooding, discriminatory post-disaster resettlement policies [39][40][41][42], and municipal differences in post-disaster land management [4,8,43].…”

Rodents harbouring zoonotic pathogens take advantage of abandoned land in post‐Katrina New Orleans

“…Yet, context and scale are critical components in predicting how relative changes in species diversity will alter pathogen transmission. In this issue of Molecular Ecology, Peterson et al (2021) examined abundance and composition of rodent communities in a highly disturbed landscape and found that Leptospira infection prevalence was actually higher at sites where rodent diversity was greatest. In addition to exotic urban species (Figure 1), additional rodent species found at unmanaged vegetated sites are native and have lower competence as pathogen reservoirs.…”

“…This is a Perspectives essay-data are associated withPeterson et al 2021, to be published concurrently. Uneven investment in post-Katrina recovery has left some neighborhoods abandoned and overgrown [Colour figure can be viewed at wileyonlinelibrary.com]…”