Date Thesis Awarded
Honors Thesis -- Open Access
Bachelors of Science (BS)
Tick-borne diseases pose a growing threat to human health globally. Many proposed environmental factors may be driving these disease patterns, but research is limited to a small number of tick species and their tick-borne diseases. Many studies to date focus on Lyme disease (causative agent Borrelia burgdorferi) in the black-legged tick (Ixodes scapularis), but little is known of other tick species and pathogens. In addition, many are limited to nymph ticks with little regard for adults. The pathogenic bacterium, Ehrlichia chaffeensis and its host, the lone star tick (Amblyomma americanum), has caused growing concern in recent years as it is the causative agent of a potentially fatal disease, Human Monocytic Ehrlichiosis. Despite increased attention, few studies have investigated long-term changes in prevalence of E. chaffeensis and many focused solely on nymphs. Here, we investigate E. chaffeensis prevalence in nymph and adult A. americanum as it pertains to seasonal weather variation over five years in the Virginia and Middle Peninsulas.
We found E. chaffeensis prevalence to vary among years with fluctuations tracking between adults and nymphs. Adults showed consistently higher prevalence, ranging from 6.5% to 23.5% and nymphs from 0.6% to 3.7%. Mixed-effect linear regression modeling relating pathogen occurrence to temperature, precipitation, humidity, and vapor pressure deficit showed similar results in both age classes. Summer precipitation was negatively associated with pathogen occurrence in adults and positively associated with nymphs. Winter temperature of the year leading up to sampling positively related to both adults and nymphs, suggesting that warmer winters projected under climate change could potentially lead to higher rates of E. chaffeensis in the lowlying lands of Southeast Virginia. Our results are temporally limited and do not account for geographic variables. Temporal broadening and spatial analyses would provide deeper insight into the study system.
Spencer, Olivia, "Five-year study highlights that variation in weather relates similarly to prevalence of Ehrlichia chaffeensis in adult and nymph lone star ticks (Amblyomma americanum)" (2020). Undergraduate Honors Theses. William & Mary. Paper 1546.