Co-infection rates of small mammal hosts in central Wisconsin
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Lyme disease is the most common vector-borne illness in the United States. This disease is caused by the spirochete Borrelia burgdorferi and is transmitted by Ixodes scapularis, the black-legged tick or deer tick. Small mammals, particularly the whitefooted mouse (Peromyscus leucopus), and some birds are important in the transmission cycle of B. burgdorferi, because they serve as reservoirs of the pathogen. These small, dark-colored ticks have a 2-year life cycle composed of four developmental stages: egg, larva, nymph, and adult. Larvae feed on small animals and can acquire B. burgdorferi infection at this stage. Nymphal and adult ticks are responsible for the transmission of the pathogen when feeding on new hosts, including humans and domestic animals. Other lesser-known infectious agents that cause disease in humans may co-occur in both hosts and vectors, thereby complicating transmission of the agents and diagnosis of disease in humans. These agents include Anaplasma phagocytophilum, various species of Ehrlichia, and Babesia microti. Both ticks and mammal hosts are primarily found in woody, brushy, or forest fragments. Recently, there has been concern that deer ticks are shifting and adapting to new reservoir hosts in more open habitats, which has major human health implications. To examine co-infections by these agents in hosts, small mammals were livetrapped at Hartman Creek State Park in 2017 and 2018 to determine the influence of host species, sex, and weight of hosts on tick burdens, singular infection rates, and coinfection rates. Peromyscus maniculatus had the highest mean of 4.57 ticks per individual, while P. leucopus had 4.33 per individual and Tamias striatus had 3.86 per individual. Sex and weight characteristics did not influence tick burdens. Of 116 mammals screened, 34 (29.3%) were singularly infected, nine mammals (7.7%) were coinfected with B. burgdorferi and A. phagocytophilum, one (0.8%) was co-infected with B. burgdorferi and B. microti, and one (0.8%) was co-infected with all three pathogens. This study found no evidence of Ehrlichia infection. By understanding the ecology and behavior of mammal reservoir hosts, valuable information can be applied to interpret and predict the transmission dynamics of these poorly understood illnesses, with the ultimate goal of decreasing the likelihood of human exposure to infected ticks.
Animals as carriers of disease