There are numerous species of paramphistomes (Paramphistomum spp, Calicophoron spp, Cotylophoron spp) in ruminants worldwide. The adult parasites are pear-shaped, pink or red, up to 15 mm long, and attach to the lining of the rumen. Immature forms are found in the duodenum and are 1–3 mm long.
Paramphistome eggs are passed in the feces, and miracidia hatch in the water and infect planorbid or bulinid snails. Development in the snail is similar to that in the life cycle of Fasciola hepatica, with the snail shedding cercariae that encyst on the herbage. In the ruminant host, the young flukes excyst and remain in the small intestine for 3–6 weeks before migrating forward through the reticulum to the rumen. Eggs are produced 7–14 weeks after infection.
Adult paramphistomes do not cause overt disease, and large numbers may be encountered. Immature paramphistomes attach to the duodenal and, at times, the ileal mucosa via a large posterior sucker. The severity of disease is associated with how deep the immature paramphistomes burrow into the mucosa and submucosal layers. Severe enteritis, possibly necrosis, and hemorrhage result. Affected animals exhibit anorexia, polydipsia, unthriftiness, and severe diarrhea. Extensive mortality may occur. Clinical signs are usually confined to young cattle, whereas goats and sheep remain susceptible throughout their lives.
The large, clear, operculated eggs are readily recognized; however, in acute paramphistomiasis there may be no eggs in the feces. Examination of the fluid feces may reveal immature flukes, many of which are passed in these cases. Diagnosis is commonly made at necropsy.
Control measures are as for the control of fascioliasis. Oxyclozanide (20 mg/kg, repeated after 72 hours) appears effective against mature flukes in sheep.
