Concurrent biodiversity loss and increases in zoonotic pathogen emergence have spurned growing interest in identifying relationships between diversity and infectious disease dynamics. A number of studies have indicated that biodiversity loss can increase the risk of pathogen and parasite transmission, especially when a pathogen is capable of infecting multiple hosts with varying competence, and when increasing diversity predictably reduces the relative abundance of the more competent host(s). In this work, we tested the hypothesis that diversity tempers disease risk by characterizing pathogenic Leptospira infection relative to rodent host diversity and abundance across a gradient of counter-urbanization in New Orleans (LA, USA).
The City of New Orleans (Louisiana, USA) presents exceptional conditions for investigating relationships between rodent diversity and risk of Leptospira infection. Catastrophic flooding and differences in post-disaster landscape management transformed the city following Hurricane Katrina in 2005. Notably, abandoned and vacant properties have accrued unevenly across the city, resulting in public health concerns that reinforce persistent legacies of sociocultural disparity. Foremost among these are gradients in rodent diversity and abundance.
In this study we assessed whether (1) Leptospira infection prevalence and load differ among rodent species; and whether (2) host abundance and infection prevalence and loads vary with species richness. To address the possibility that risk is driven by spill over among co-occurring host species, we also assessed whether (3) the same Leptospira species infect different host species, including different species found at the same location. Finally, we assessed whether (4) environmental, rodent assemblage, or host features best predict Leptospira infection in rodents to assess the nature and range of conditions that shape disease risk across post-Katrina New Orleans.
Results/Conclusions
We found variation in infection loads and prevalence among rodent host species. Additionally, we found that Leptospira infection loads were higher in urban areas with a greater number of rodent species. Areas with higher species richness also harbored a greater abundance of hosts, including the most competent hosts, indicating that the observed amplification effect reflects shifts in overall and relative host abundance. We also found evidence of potential spillover of Leptospira species among rodent hosts. Suggesting that cross-species transmission of Leptospira likely increases infection at sites with greater syntopy. Evidence that rodent diversity and Leptospira infection load parallel abandonment indicates that ‘greening’ from counter-urbanization can elevate zoonotic disease risk within cities, particularly in underserved communities that are burdened with disproportionate concentrations of abandoned and vacant properties.