Theory predicts that a primary impact of global climate change on vector-borne disease transmission will be shifts in or expansion of current vector ranges. However, few empirical studies have investigated potential mechanisms by which this could occur. Knowledge of current tick and pathogen distributions and their determinants is essential to develop accurate predictive models of the impacts of climate change on tick-borne disease. The consequences of climate change for tick distributions in Central America have received scant attention, despite the presence of several important tick-borne diseases. This study evaluates relative contributions of abiotic and biotic factors in controlling current tick and tick-borne pathogen distributions in Panama, which will inform predictions of how pathogen exposure risk will be impacted by climate change. Field efforts were conducted throughout twenty-four months at three sites spanning a natural precipitation gradient across Panama, which provides a proxy for future climate change, wherein conditions at the driest site represent the predicted result of climate change for wetter regions. Tick abundance and survival were monitored weekly at each of these sites, and local mammal species richness was estimated using camera traps. Pathogen screening of ticks was performed using polymerase chain reaction and reverse line blot hybridization.
Overall, tick abundances were significantly higher at the medium and dry sites compared to the wet site. Results from generalized linear mixed models suggest that abundance of adults is negatively related to precipitation. However, juvenile life stages display genus-level differences in associations with precipitation. Overall, juvenile ticks experienced higher mortality than adults, but both life stages experienced highest mortality at the dry site and in the dry season, suggesting that conditions at the dry end of the gradient are more stressful. Preliminary pathogen screening indicated that 12.3% of ticks tested were infected with Spotted Fever Group Rickettsiae. Together, my preliminary results suggest that under projected drier conditions induced by climate change, an increase in tick abundance may be offset by an increase in tick mortality, requiring a sophisticated modeling approach to understand the relative contributions of each factor. Ultimately, I will use pathogen data in combination with field data on tick distribution, tick survival, and mammal communities to construct a structural equation model to estimate the potential effects of climate change on tick-borne disease risk. The applicability of this model extends beyond this disease system and can serve as a framework for studies of climate change-vector interactions in other regions.