This experimental study was conducted to evaluate the susceptibility of American bison (Bison bison) to liver flukes, Fascioloides magna and Fasciola hepatica. Six bison were each experimentally inoculated with 600 metacercariae of Fascioloides magna, and three were later treated with triclabendazole suspension at 40 mg/kg of body weight. Four additional bison were each experimentally inoculated with 600 metacercariae of Fasciola hepatica. Five control bison were placebo controls. Two controls and all inoculated bison were euthanized 10 mo (Fascioloides magna) and 7 mo (Fasciola hepatica) after inoculation. None of the control bison or the bison inoculated with Fascioloides magna had flukes or lesions characteristic of fluke infection at necropsy. All four bison inoculated with Fasciola hepatica had characteristic liver fluke lesions at necropsy, and three of four bison contained four, 103, and 111 adult flukes, respectively. Fluke eggs were detected in feces of all Fasciola hepatica–inoculated bison during the experiment, but not from the Fascioloides magna–infected bison or control bison. Clinical signs of infection were not observed during the experiment, but hemoglobin and packed cell volumes were lower in the Fasciola hepatica bison when compared to controls, and eosinophil levels were increased. Triclabendazole at 40 mg/kg of body weight appeared to be safe in bison because no toxic reactions were observed. Results from this study indicated bison are susceptible to infection with Fasciola hepatica and are efficient definitive hosts. Because no Fascioloides magna were recovered, bison may have a decreased susceptibility or innate resistance to Fascioloides magna infection, which may account for a lack of reported infections in this host.

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