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Grand Teton National Park Report

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The role of parasitism, whether macro- or microparasites, and whether endo- or ectoparasites, in the demographic machinery of microtines is poorly understood. In a review of the parasites of Microtus, Timm (1985) lists no protozoan endoparasites whatsoever for this genus and observes that one of the most challenging and fruitful directions of future research with Microtus will be the statistical quantification of the cost of parasitism. Babesia microti, a parasitic protozoan, is transmitted by a tick vector and reproduces in the erythrocytes of its mammalian host. Initially, Babesia was thought to be restricted to small mammals, however, in 1970 the first human cases were diagnosed in residents of Nantucket Island, Massachusetts (Western et al. 1970). In the United States, human babesiosis is caused by B. microti. As hunians insert themselves into places where they have historically been present only occasionally, they often contract new diseases. A second protozoan parasite, Hepatozoon sp., which is widespread in small mammals in Europe, is also found in reptiles throughout the world. The record of Hepatozoon in North American small mammals is not extensive. Like Babesia, Hepatozoon is a two-host parasite. Unlike Babesia, for which the intermediate host is always a tick, the intermediate host of Hepatozoon may be a tick, a mite, a flea, or a mosquito. The method of transmission by the vector also differs in the two parasites. Babesia is transmitted in the tick's saliva when it bites, whereas Hepatozoon infection requires the vertebrate host to swallow the vector. In our 1995 studies, we sought more data on these two parasites. The objectives for 1995 were: to sample specific populations of M. montanus, in which we have previously documented Hepatozoon infections, to determine whether there were differences in the infection rates at different study sites in the park, and to search for any additional vectors of Hepatozoon sp. infections in M. montanus by examining ectoparasites. Our long-term objectives are to document the effects and cost of parasitism on M. montanus populations.