pathogens, and transient commensals (colonizing the tick without marked detrimental effects), or as pathogens (see Clay and Fuqua, Appendix A).

In this chapter, five scientists examined the natural history of ticks and their wildlife and domestic hosts; outlined the contributions of animal health experts to understanding human TBD; explored genetic diversity among pathogens, vectors, and hosts; and showed how scientists investigate the microbial community found within the ticks to better understand the human risk for tick-borne diseases.


Ulrike G. Munderloh, D.V.M., Ph.D. Department of Entomology, University of Minnesota

Ticks are efficient vectors of multiple pathogens due to their potential interactions with several different vertebrate hosts during their life cycle. As a result, they have the opportunity to acquire a large array of different types of organisms that are present in the blood of these hosts. The microbial community in ticks includes viruses, bacteria, protozoa, and fungi, and serve as symbionts, commensals, and pathogens. In fact, the organisms that comprise the tick microbiome vastly outnumber recognized human pathogens. This microbial community can influence the acquisition, transmission, and virulence of human pathogens. Furthermore, as the tick feeds for extended periods, it interacts with its vertebrate host and has the ability to suppress the host’s immune system by dampening down the immune response and binding up antibodies that the host might have made in an attempt to rid itself of the blood-sucking parasite. These attributes ensure that a pathogen can be acquired from or transmitted to a bite site that is suppressed and immunologically inactive.

Anaplasma phagocytophilum shares a vector, the black-legged tick, with Lyme disease spirochetes, a vector that is expanding its range, which helps to explain the increasing incidence of human granulocytic anaplasmosis. The white blood cells, specifically the neutrophils, are infected in reservoir mammalian hosts in the peripheral blood, and in lungs, heart, spleen, and gut. Animals also serve as models to account for the multiple signs of disease that infected people may present. There is a need to understand how these pathogens can survive and flourish in a broad range of mammalian hosts and a number of organs within the host, as well as in vector ticks. This can be done with new techniques to analyze how microbes use their genomes during passage in mammals and ticks. Live imaging can further reveal in real time how arthropod-associated pathogens and symbionts

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