Distribution and Abundance of the Tick-Borne Piroplasm Theileria cervi Parasitizing White-Tailed Deer (Odocoileus virginianus) in Massachusetts

Pathogen surveillance contributes to the prediction of outbreaks and implementation of strategies to minimize disease transmission. White-tailed deer (Odocoileus virginianus) host important disease vectors and often support the proliferation of associated pathogens. Such vectors include ticks: hematophagous acarids that facilitate pathogen transmission between animals through blood feeding. Piroplasmida, an order of blood-borne protozoa including Babesia and Theileria, exploits this feeding to infect definitive hosts. Accordingly, we investigated the prevalence of Theileria cervi infections in Massachusetts white-tailed deer. Conventional polymerase chain reaction (PCR) was used to detect parasite gene fragments encoding the small ribosomal subunit (18S rRNA). Confirmation of species identity was determined by Oxford nanopore sequencing and Sequencher analysis. This revealed a 32.6% prevalence of T. cervi across Massachusetts. Whilst surveillance of deer blood uncovers parasite abundance and distribution, inversely, this allows us to also monitor vector populations. As Amblyomma americanum is the only vector implicated in the transmission of T. cervi, the detection of T. cervi in regions without anticipated Amblyomma presence may indicate expansion of vector populations. These findings provide valuable insights into the prevalence and ecology of this piroplasm and its vector, with possible implications for veterinary and public health.