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Ectoparasites of Big Brown Bats

Ectoparasites of the urban population of big brown bats in Fort Collins were investigated during summers 2002, 2003, and 2004. Eleven species of ectoparasites were found (Acanthophthirius caudata, Alabidocarpus eptesicus, Basilia forcipata, Carios kelleyi, Cimex pilosellus, Demodex sp., Leptotrombidium myotis, Myodopsylla borealis, Pteracarus aculeus, Spinturnix bakeri, and Steatonyssus occidentalis). Five species were analyzed by prevalence and intensity (C. pilosellus, M. borealis, L. myotis, S. bakeri, and S. occidentalis) based on 2,161 counts of 1,702 marked individual bats over the 3 summer study periods. We investigated 4 factors potentially influencing prevalence and intensity: age class of the host, reproductive status of adult female hosts, roosts in which the hosts were found, and abiotic conditions during the years sampled. The macronyssid mite, S. occidentalis, was the most prevalent and abundant ectoparasite. Adult bats tended to have more ectoparasites than volant juveniles for most of the species analyzed. In a sample of known age bats at one large colony, bats of 4 years of age or greater tended to have a higher ectoparasite load of S. occidentalis and S. bakeri when compared to younger bats. Lactating female bats had the highest prevalence and intensities of most ectoparasites. Annual differences in ectoparasite prevalence and intensity were related to temperature and humidity, which can affect the nidicolous species of ectoparasites. Residents of 2 buildings sprayed insecticides in response to Cimex, and this appeared to reduce ectoparasitism in 2 of the 3 species present at these buildings. Intensity of the abundant S. occidentalis had no influence on annual survival of big brown bats.

Recently, bat ectoparasites have been demonstrated to harbor pathogens of potential importance to humans. We conducted a post-hoc analysis to investigate the relative importance of colony size, year, age class, colony size and year interaction, as well as intensities of three ectoparasite species (Steatonyssus occidentalis, Cimex pilosellus, and Spinturnix bakeri) in exposure of big brown bats (Eptesicus fuscus) to the rabies virus. We utilized serum samples and ectoparasite counts collected on big brown bats in 2002 and 2003. We found that colony size and year were the most important variables associated with exposure of rabies virus in big brown bats using logistic regression and AIC model selection procedures. Two ectoparasites (S. occidentalis and S. bakeri) were also relatively important in AICc models explaining seroprevalence of antirabies antibodies. However, both ectoparasites had higher intensities on seronegative rather than seropositive bats, suggesting that these ectoparasites do not directly influence exposure patterns of big brown bats to the rabies virus.

Cimex pilosellus (Bat bug)

Steatonyssus occidentalis (female)

Steatonyssus occidentalis (nymph)

Leptotrombidium myotis

Basilia forcipata

Carios kelleyi

Myodopsylla borealis

Alabidocarpus eptesicus

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