An Analysis of The Influence of Human Disease Pathogens on Core Behaviors of The Black-Legged Tick

Ixodes scapularis, the black-legged or deer tick, is a vector for several different disease-causing microbes, including the causative agent of Lyme disease. As such, it is a major health concern for people living within its range in the eastern half of the United States, a habitation area that is increasing due to climate change. Despite its medical relevance as a disease vector, there is still much to learn about the basic behavior of these arachnids in the wild. Thus, the major hypothesis of this thesis is that ticks that are infected with specific human disease-causing microbes behave differently than those that are free of those pathogens. If the hypothesis is correct, this information might be used to develop more effective ways to control or prevent bites from pathogen-infected animals. My thesis analyzed 143 wild-caught ticks from 3 counties in Western Pennsylvania. I tested each tick for its activity over 1 day, a response to a stimulatory puff of carbon dioxide, and their respiration over 4 hours. After the behavioral analyses were complete, the ticks were molecularly characterized to ascertain if any human disease pathogens were present. Although 44 ticks were infected with Borrelia burgdorferi (the pathogen that causes Lyme disease), 16 were infected with Anaplasma phagocytophilum (the pathogen that causes anaplasmosis), 12 were infected Babesia microti (the causative agent of babesiosis), 2 were infected with Borrelia miyamotoi (the pathogen that causes Borrelia miyamotoi disease), 1 was infected with virus that causes Powassan virus disease, 8 were co-infected with two pathogens, and 2 were co-infected with 3 pathogens, none of these ticks displayed behaviors that were significantly different from the wild-caught animals that were free from the above pathogens. The implications of this study are that the ticks infected with specific human pathogens do not grossly affect their overall behavior, perhaps because the microbe load of the pathogens is small in comparison to the overall microbiota of animals in the wild. It is interesting to note that there are some reports of infection with human disease pathogens affecting the behavior of lab-reared ticks, so increasing the number of animals to assay in order to determine if more subtle differences occur would be a goal of future research.