Zoonotic pathogens are the leading drivers of emerging infectious diseases in humans, and a complex suite of interactions among pathogens, hosts, and the environment can drive their emergence and spread. Zoonotic pathogens are capable of infecting more than one host species, and growing evidence suggests that community-wide host-pathogen interactions can influence disease risk. While urban areas often support reduced host diversity relative to less urbanized areas, some zoonotic host species, such as rodents, can become hyper-abundant in urban systems. Growing evidence suggests that urban rodent populations are frequently but heterogeneously infected with pathogens of human health concern, but additional study is needed to identify the relative importance of abiotic and biotic factors across scales in driving zoonotic pathogen infection in urban rodent populations.
In this study, we clarify the relative importance of environmental, community, population and individual-level factors in predicting (1) prevalence of zoonotic pathogen infection and (2) zoonotic pathogen load across a gradient of urbanization in New Orleans, Louisiana. We focused on pathogenic Leptospira, which are considered neglected pathogens of concern, but which are also the most common bacterial zoonosis worldwide. Using standardized live-trapping, we assessed rodent abundance and diversity, as well as Leptospira prevalence and quantitative infection load in rodents from four study areas (three urban neighborhoods and one uninhabited area) during summer and winter seasons over two consecutive years. We paired these on-the-ground assessments with satellite-derived imagery to determine the relative importance of abiotic and individual-to-community level factors in predicting Leptospira infection in rodent hosts.
We detected five rodent species in our New Orleans study system, with up to four species collected from a single trapping location. Results indicate that across all species Leptospira prevalence is ~27%. We have detected Leptospira infection in three rodent hosts, including the commensal species: Mus musculus (~25% infected), Rattus rattus (~20% infected) and Rattus norvegicus (~40% infected). After controlling for year, we did not find that species identity was a significant predictor of Leptospira infection, though we did find evidence of seasonal variation in infection. As in other recent studies of zoonotic infection in urban rodents, we found that Leptospira infection is geographically heterogeneous across the New Orleans study system. Landscape features, as well as host population and community-level factors may predict prevalence of infection in urban rodents.