Paramphistomum microbothrioides in American bison and domestic beef cattle.

Intestinal paramphistomiosis was diagnosed in a bull and cow with severe diarrhea and weight loss, and subsequent investigation suggested that the infection was transmitted from American bison (Bison bison). The rumen fluke, Paramphistomum microbothrioides, was recovered from the rumen of 3 bison on the farm or origin. Single operculate eggs of P microbothrioides measuring 130 x 69 micrometers were recovered from the feces of the bull, from 9 of 10 bison, and from 3 of 9 other beef cattle. Snails of the genera Physa and Helisoma were collected at the farm of origin. Ostertagiosis and paratuberculosis were considered in the differential diagnosis but were ruled out on the basis of fecal, plasma, and mucosal tests. In view of the lack of approved drugs for treatment of paramphistomes in the United States, treatment was attempted with an 8 times normal dose of thiabendazole (528 mg/kg). Advice was given on grazing management strategies designed to reduce exposure of susceptible cattle to metacercariae, and the owner was advised to drain a large snail habitat.