Host abundance, distribution, and infection with two tickborne pathogens, Babesia microti and Borrelia burgdorferi in small mammals in western Pennsylvania

In the United States, tick-borne diseases are the most common vector-borne disease. Pennsylvania is consistently one of the top states for Lyme disease cases, caused by Borrelia burgdorferi bacteria. Human babesiosis, caused by Babesia microti, is endemic in the northeastern United States, but is not a reportable condition in Pennsylvania. These pathogens are transmitted through Ixodes scapularis tick vectors, which are found throughout Pennsylvania. Tick-borne pathogens, like B. burgdorferi and B. microti, are maintained in an enzootic cycle between I. scapularis ticks and a reservoir host. Peromyscus leucopus, the white-footed mouse, is considered the most competent mammalian host for both B. burgdorferi and B. microti. This study examined the abundance, distribution, and pathogen infection prevalence among small mammal hosts in southwestern Pennsylvania over a three-year collection period between 2021-2023. The most abundant species included white-footed mice, Eastern chipmunks, and shrews. These species were infected with B. burgdorferi at similar prevalences, but white-footed mice and chipmunks had significantly higher prevalence of B. microti compared to shrews, suggesting that these species are important for maintaining infection in the tick population. Collection sites were analyzed based on community type with the prevalence of B. burgdorferi being similar in urban and rural sites, but lower in suburban areas, suggesting differences in public health risks for Lyme disease. The prevalence of B. microti did not differ between community types. This study is the first to describe the establishment of B. microti among small mammal hosts in southwestern Pennsylvania.