PROJECT SUMMARY/ABSTRACT
The south-central U.S. has among the highest human incidences of tick-borne diseases (TbDs) like spotted
fever group rickettsiosis and Ehrlichiosis. Yet, it is one of the least-studied regions with regard to the ecology of
tick species and hosts, and their associations with human-caused environmental change. A pervasive form of
human-caused land cover change ongoing globally, including in the south-central U.S., is encroachment of
woody plants in grasslands and shrublands (woody plant encroachment; WPE). WPE’s ecological impacts
(e.g., alteration of microclimates and arthropod communities) mirror mechanisms by which other land cover
changes influence transmission of pathogens, including tick-borne pathogens (TbPs). However, WPE’s
wholesale transformation of ecosystems makes it fundamentally different from other well-studied woody cover
changes like deforestation and non-native shrub invasions in forests. A virtually unstudied consequence of
WPE is its potential foundational role in influencing distributions of tick vectors and spatiotemporal patterns of
TbP transmission. Our long-term goal is to clarify how WPE affects tick-borne diseases in the south-central
U.S., and to apply this knowledge to better predict human disease risk and target public health resources and
WPE management that benefit human health. Our overall aim is to assess relationships between WPE by
eastern redcedar (ERC; Juniperus virginiana), the primary encroaching species in the south-central U.S, and
TbP transmission systems in Oklahoma (where WPE extent is 5-7x greater than elsewhere in the U.S.). Our
central hypothesis is that the many WPE-caused changes to ecosystems facilitate spatial expansion and
persistence of key tick vectors and increase rates of vector infection for multiple pathogens. To address this
hypothesis, we propose 2 objectives: 1) Quantify tick abundance and diversity relative to ERC encroachment;
and 2) Evaluate links between TbP infection prevalence and ERC encroachment. Preliminary studies indicate
that numbers of key tick species (Amblyomma americanum & Dermacentor variabilis), and of ticks infected
with SFG rickettsia and Ehrlichia spp., are higher with ERC encroachment. This study will include 2 years of
field sampling ticks at 40 sites representing 4 ERC encroachment stages, including control sites with no ERC.
Ticks will be identified and tested for 5 pathogen groups, and we will analyze whether ERC stage is related to
tick diversity, abundance, and TbP prevalence. This study is innovative because no research globally has
considered effects of WPE under a whole-disease system framework. Addressing our objectives will increase
understanding of WPE’s impact on ticks and TbP transmission dynamics; future research will address other
mechanisms including WPE effects on reservoir hosts and tick-host interactions. This study will provide critical
information that improves public health by informing tick control strategies based on assessment of land cover
characteristics, and by focusing distribution of public health resources and enactment of WPE management.
