Tracking an invader: Population genetics and the use of passive wildlife surveillance to determine the distribution and host range of ticks and the exotic Haemaphysalis longicornis

The exotic Haemaphysalis longicornis, the Asian longhorned tick, was recently detected in the United States in 2017, however archived specimens indicate that this species has been present in the United States since as early as 2010. Since its initial detection, SCWDS has been involved in research and surveillance to its population biology, pathogens, and dispersal. In general, we have developed a novel molecular assay to aide in the identification of Haemaphysalis ticks and this assay combined with passive and active surveillance has confirmed H. longicornis  in eight states in a variety of habitats (hardwood forests, grassy fields, and manicured lawns) and on a numerous host species including human, companion animal, livestock, and wildlife indicating that this tick is a habitat and host generalist. These detections resulted in some of the first host, county, and state records for H. longicornis in the United States. Additionally, pathogen surveillance detected a 12.7% prevalence of the exotic piroplasm parasite, Theileria oreintalis Ikeda, in host seeking H. longicornis from Virginia. Finally, using a restriction-site-associated DNA (RAD) sequencing approach to observe nucleotide differences across the genome, we found that native populations of H. longicornis are more diverse than introduced and invasive populations. Additional genetic variation detected within the United Sates suggests that there could have been at least five introductory events. Collectively, these studies answer important questions on the natural history of H. longicornis in the United States and what potential impacts it may have for the health of humans and animals.