PS 52-196 - Ecological and social factors impact pathogen burden in invasive rodents around the world

Background/Question/Methods

Commensal rodent populations are increasing globally, particularly invasive rats in cities. In addition to detrimental impacts on local ecosystems, this increases the risks of human-rat interactions and potential zoonoses. Rattus rattus and Rattus norvegicus are the two most widely distributed species of rats, with a near-global range. The aim of this study is to understand the connection between ecological and socioeconomic factors that influence pathogen load and disease burden in rats. We tested three hypotheses: (1) rats will harbor more pathogens/parasites in habitats with lower biodiversity, consistent with the dilution effect; (2) there will be a higher parasite burden in rats in regions with lower sanitation scores, GDP, and Gini Index; and (3) pathogen/parasite prevalence will increase along an urbanization gradient. To test these hypotheses, we performed a meta-analysis on a global scale. We extracted our data from papers in the Web of Science database, and collected the environmental and socioeconomic datasets from additional databases. We independently developed an urbanicity index using GIS spatial analysis.

Results/Conclusions

Our initial search returned 636 studies that we assessed for eligibility. From those, 242 studies are included in our final dataset, and 903 data points were extracted for analysis. Our dataset includes data from 64 countries and 205 pathogen or parasite species. The top pathogen represented was Leptospira spp., Bartonella spp., Toxoplasma gondii, Capillaria hepatica, and Leishmania spp. The pathogen/parasite that was tested for the most was Leptospira spp., and the pathogen/parasite that had the highest overall percent positivity was C. hepatica, a common nematode. Higher biodiversity levels were associated with lower overall pathogen/parasite burden in these rats. We also found a negative correlation between 3 of the 4 socioeconomic variables and rodent disease burden. Urbanization, temperature, precipitation, and canopy levels were not associated with pathogen/parasite load. The analyses point to the value of knowledge we can gain from looking at environmental and social factors in predicting disease prevalence. There is clearly a public health interest in understanding the disease ecology of commensal rodents and the pathogens they vector. But our study also provides a baseline understanding of the ecological correlates of infection risk, and how to use global data on rat disease ecology to make predictions in unstudied areas.