Abiotic and biotic determinants of tick-borne disease risk in Central Panama

As the incidence of tick-borne disease rises globally, the need for comprehensive research into the underlying mechanisms of tick and pathogen distributions becomes increasingly urgent. Hard ticks are ectoparasites that typically feed on a vertebrate host once during each of three life stages and transmit pathogens of public health, conservation, and agricultural importance. Tick distributions are strongly influenced by abiotic factors, including temperature and humidity, and spatial abundance and temporal activity patterns vary among tick species and life stages. Abiotic variables influence off-host tick survival and may define the limits of a tick’s geographic range. However, successful completion of the life cycle is also governed by biotic factors, including abundance, composition, and diversity of vertebrate hosts. The influence of abiotic and biotic factors on tick distributions in turn affects tick-borne pathogen distributions, creating a heterogenous landscape of tick-borne disease risk. Therefore, knowledge of both abiotic and biotic determinants of current tick distributions is essential to develop accurate predictive models of the impacts of global change on future distributions of medically-important ticks and their associated pathogens. This dissertation integrates field research, conducted across three national parks spanning a precipitation gradient in Central Panama, with laboratory research on infection prevalence, to examine the abiotic and biotic determinants of tick-borne disease risk. Longitudinal tick surveys, experimental survival enclosures, and genomic screening for fungal pathogens indicated that host-seeking activity and spatial abundance patterns aligned with abiotically favorable periods for survival for several tick species and life stages. Next-generation sequencing of collected ticks for potential pathogens indicated a high overall prevalence and diversity of tick-borne pathogens, with twelve known or suspected pathogens detected, including several previously unreported in Panama. While spatial distribution of pathogens did not vary among study sites, prevalence varied both seasonally and among tick life stages for several pathogens. Notably, there was higher prevalence of rickettsial infection in the dry season and higher Ehrlichia spp. prevalence in nymphal ticks compared to adults. Camera traps were deployed to assess relationships among overall diversity, species richness, community composition, and relative abundance of terrestrial mammal species, tick species, and tick-borne pathogen species. Relative abundance of ticks was not correlated with relative abundance of associated mammal hosts. However, significant associations among mammal abundance and pathogen prevalence in ticks were detected for several mammalian species, implicating these mammal species as reservoir hosts for these pathogens. These efforts demonstrate that integrating camera trapping and pathogen screening data can be utilized as a non-invasive tool to identify potential reservoir species, leading to more targeted studies in the future. Together, this dissertation represents a comprehensive examination of the abiotic and biotic factors underlying tick-borne disease risk in Central Panama. This knowledge can be used not only to identify areas of elevated tick-borne disease risk under current climate and land-use conditions but can also be integrated into climate or land-use models to estimate how disease risk may shift as a result of future environmental change. The applicability of this research extends beyond this disease system and can serve as a framework for host-vector-pathogen studies in other regions.LimitedAuthor requested closed access (OA after 2yrs) in Vireo ETD syste