Investigations of leptospira in small mammalian host species in the Hawaiian islands

Abstract

Considered the most widespread and prevalent of zoonoses, the emergent infectious leptospirosis disease is found throughout tropical regions in particular, with annual mean incidence rates in Hawaii consistently the highest in the United States. As a tropical archipelago with relatively low host and leptospiral diversity, Hawaii represents an exceptional opportunity for investigations in the ecology and evolution of this bacterial pathogen. In an effort to gain a better understanding of disease transmission dynamics and environmental drivers in Hawaii, the studies presented in this dissertation each take a distinct approach to examining the associations between three main components underlying the ecology of leptospirosis across the archipelago; namely, the Leptospira pathogen, animal hosts, and climate. First, I employed a longitudinal dataset of animal infection prevalence from a period of 14 consecutive years across five maintenance host species and three main islands to describe the epizootiological distribution of pathogenic leptospires in Hawaii. In a second study, I combined field biology and molecular lab techniques to characterize the 16S rRNA genetic diversity of Leptospira amongst a community of small mammals in a local rainforest. Finally, Hosmer-Lemeshow goodness-of-fit and Wald assessments of multivariate logistic regression models were used to investigate the association between rainfall and leptospiral animal infection prevalence at multiple spatio-temporal scales. The key findings in this dissertation address evolutionary patterns of host specificity, provide a preliminary examination of leptospiral genetic diversity in host vectors, and show that precipitation is an environmental driver of host infection prevalence at specific spatial and temporal scales. These results shed light on leptospiral transmission dynamics in a tropical region enzootic for the bacterial pathogen, and lay the foundation for an integrated eco-evolutionary model of leptospirosis in Hawaii.