Tick species and tick-borne disease surveillance in southern Illinois

Author

Victoria Phillips, Southern Illinois University CarbondaleFollow

Date of Award

12-1-2020

Degree Name

Master of Science

Department

Zoology

First Advisor

Jiménez, Agustín

Abstract

Human alteration of the landscape and environment is favoring the expansion of ticks and the pathogens they vector throughout the United States. The changes in these distributions are documented through literature and the deposition of specimens in scientific collections. In southern Illinois, tick species records are sporadic and inconsistent with what is actually found in the region. This information is necessary for public health officials to develop prevention strategies against tick-borne illnesses. I conducted research from 2018-2020 to accomplish the following: (1) conduct a ticks species and tick-borne disease survey of southern Illinois, (2) create habitat maps for Amblyomma americanum and Dermacentor variabilis in the region, and (3) attempt to identify microhabitat variables influencing tick abundance. To accomplish my first objective, I sampled 26 sites from 11 counties in southern Illinois utilizing the tick drag method. Ticks were then tested for their associated pathogens using quantitative PCR. Four species of tick, Amblyomma americanum (the lone star tick), Dermacentor variabilis (the American dog tick), Ixodes scapularis (the black-legged deer tick), and Amblyomma maculatum (the Gulf Coast tick) were identified. Rickettsia rickettsii and Rickettsia parkeri causative agents of human rickettsiosis, Ehrilichia ewingii and Ehrlichia chaffeensis, causative agents of human granulocytic ehrlichiosis, and Rickettsia amblyommii whose effects are not known, were all found in the study region. The second objective, lone star and American dog tick species distribution models (SDMs), was accomplished using the popular SDM program, Maxent. Maxent uses species presence data and their associated environmental characteristics to create predictions of habitat suitability. The resulting models indicate a correlation for both species with the Shawnee National Forest, likely due to the fragmented habitat structure as indicated by the strong impact of cultivated and managed vegetation on both species models. Lastly, I attempted to identify microhabitat characteristics that influence tick species abundance. Temperature, humidity, canopy closure, and wind speed were measured and recorded and vegetation density estimates and soil moisture were recorded categorically at each site, each visit. Using a chi-squared test I proved that tick abundance is not static, and varies throughout the summer months. I then used a principal component analysis (PCA) to assess correlation between habitat variables and tick abundance, but no signal was detected. This study established a baseline for tick species and tick-borne disease presence in southern Illinois. The information resulting from this study can be used to inform public health officials and inform future tick-borne disease prevention strategies. I recommend continued surveillance of the area to monitor species distributions and resulting pathogen risk to residents.