Vector-borne disease exposure and transmission is influenced through multiple pathways affecting vector abundances. Despite the major threat to public health from vector-borne diseases the relative importance of direct versus indirect drivers, and whether the interrelated effects of multiple pathways on vector abundances are synergistic or antagonistic, are poorly understood. We are working to disentangle the relative effects of direct factors such as host density, from indirect factors, such as land management, on the risk of exposure to tick-borne diseases (TBDs). Specifically, we are examining the effects of fire management and resulting vegetation composition and structure on the densities of ticks and wildlife hosts on Department of Defense (DoD) installations across the Southeast United States. Our overarching hypothesis is that fire management and vegetation communities are dominant and interrelated factors affecting exposure risk to TBDs. During 2017 and 2018 we established 95 plots across nine DoD installations primarily in pine-dominated landscapes that last experienced fire between 0 and 11 years ago. In each plot, we measured tree basal area and density, quantified plant community diversity and structure, and quantified densities of ticks and their wildlife-hosts.
Results/Conclusions
A path analysis revealed that time since fire was the dominant factor influencing tick density. Increasing time since fire had a direct positive effect on tick density and an indirect positive effect through increasing litter biomass and overstory canopy cover. Interestingly, we did not find a direct effect of host density on tick density, nor a relationship between host density and time since fire. The lack of relationship between host density and tick density suggests that microclimate conditions and associated drivers such as vegetation are more important than host densities for predicting tick densities in these landscapes. Our results provide evidence that fire and forest vegetation structure are related factors affecting TBD risk as we predicted. In addition to direct destruction of ticks, fires reduce vegetation and litter cover, likely resulting in hotter and drier microclimates that are less favorable for tick survival. More frequent application of prescribed fires, a key management tool in maintaining pine ecosystems in the southeastern US, may also protect public health by lowering tick abundances and TBD risk in these landscapes.