Ecology and Climate Tolerance of Emerging Tick Disease Vectors in Central Appalachia/Southwestern Virginia

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Virginia Tech

Little is known about the tick populations found within the central Appalachian/southwestern region of Virginia. The main focus of this research was to better assess local tick communities in the central Appalachian-Southwestern region of Virginia, which was addressed by determining species diversity, habitat associations, seasonal phenology, pathogen prevalence, and ecological factors that influences tick presence and abundance. A field study was conducted from June 2019 - November 2020 across 8 counties and 3 habitat types. Forested habitats exhibited greater tick species diversity than pasture and urban habitats. Each tick species was observed to be associated with particular habitats. The presence of B. burgdorferi sensu stricto (causative agent of Lyme disease), the human variant of A. phagocytophilum (causative agent of human granulocytic anaplasmosis), and Powassan virus (the causative agent of Powassan encephalitis) were detected in collected field specimens, suggesting a significant threat to public health. The detection of Powassan virus RNA in local Ixodes scapularis ticks is the first evidence of this viral pathogen within the region.

The overwintering abilities of ticks, whose populations are expanding or becoming more invasive, including Haemaphysalis longicornis, Amblyomma americanum, and Amblyomma maculatum, were examined through a combination of laboratory and field experiments. Amblyomma americanum and H. longicornis nymphal ticks had a lower supercooling temperature than adult ticks, suggesting their potential to overwinter better; A. maculatum nymphs had similar average supercooling temperatures as the other two species at nymphal stage. Via a field experiment, A. americanum, H. longicornis, and A. maculatum were subjected to natural elements of a Virginian winter in a two-factor design investigating elevation and potential insulation coverage. Elevation and insulation coverage were found to have no significant impact on the overwintering survival of H. longicornis and A. americanum. However, the life-stage of the tick was determined to be a significant factor that dictated the survival of ticks of these species. Overwintering survival of Amblyomma maculatum nymphs was influenced by insulation (proxied by leaf litter); which may be attributed to this tick's preference of drier climate. Low overwintering survival suggests that a tick may not be able to establish a permanent population within the area.

ticks, vector ecology, phenology, species diversity, seasonality, pathogen prevalence, overwintering, freezing tolerance