Effect of woody plant encroachment by eastern redcedar on the abundance of ticks and prevalence of tick-borne pathogens

Tick-borne pathogens are the most common vector-borne diseases in the United States, accounting for over 75% of nationally reported cases. Over the past two decades, several tick-borne diseases, including Ehrlichiosis and Spotted Fever Group Rickettsiosis, have increased. Additionally, two relatively new pathogens, Panola Mountain Ehrlichia and Borrelia lonestari, have emerged, posing risks to human health. As the distribution of medically important ticks and pathogens continues to increase, it is crucial to understand the factors driving their expansion. To address this gap, we examined how woody plant encroachment by eastern redcedar (Juniperus virginiana, ERC) influences tick ecology by assessing the abundance of three tick species, Amblyomma americanum, Dermacentor variabilis, and Amblyomma maculatum, in grasslands undergoing ERC encroachment in Oklahoma. We also investigated the prevalence of tick-borne pathogens detected within these ticks and evaluated whether pathogen prevalence varies across different stages of ERC encroachment. Our study found that ERC encroachment in the southern Great Plains creates favorable conditions for higher densities of A. americanum and D. variabilis compared to open grasslands. Furthermore, distinct species-specific patterns emerged, with tick densities significantly correlated with different levels of ERC encroachment. Although species-specific trends exist, our results show that early-stage ERC encroachment supports the highest tick densities compared to open grasslands and more densely encroached areas. While no significant differences were found in the prevalence of four Rickettsia species or B. lonestari across encroachment stages, Ehrlichia prevalence in A. americanum varied significantly among stages. This suggests that the most effective strategy to reduce tick populations in grasslands is to prevent ERC encroachment early or remove it before it progresses. Landowners, managers of public and private lands, and public health officials should be aware of the health risks associated with ERC encroachment and consider new educational and management protocols to protect their communities.