Paramphlstomum cervi, Paramphlstomum microbothrlum, Cotylophoron cotylophorum
Light red, pear-shaped flukes, 5 to 13 mm long and 2 to 5 mm wide with a large posterior sucker.
Indirect, with a variety of aquatic snails as intermediate hosts. Eggs pass in feces; the miracidium hatches in 12 to 17 days and swims free in water before penetrating a snail. Cercariae which develop and mature in the snails, are shed, and encyst as metacercariae on vegetation. Total development in snails requires about 34 days. The metacercariae may live on pasture for about three months. Sheep are infected by ingesting cysts on grass. Digestion releases metacercariae in the intestine where they attach and mature for 6 to 8 weeks before migrating forward to the rumen. Prepatent period is 3 to 4 months.
Rumen; immature forms live in small intestine.
Infected sheep do not feed or digest efficiently and become unthrifty.
Effect on Host:
Immature flukes attached to the wall of the small intestine cause serious inflammation. Digestion and absorption are impaired; bleeding may occur. Appetite is also depressed. Infected animals, therefore, eat less; what feed is consumed is incompletely digested and absorbed. Diarrhea results. Sheep lose weight and become weak. Bleeding for a prolonged period may cause anemia to occur, which further weakens the host.
Eggs in feces indicate presence of adult rumen flukes, which themselves do not cause disease. Demonstration of the diarrhea is a better indication of damage being caused by immature flukes of Paramphistomum cervi.
Paramphistomum egg (fig.1)
Length 160 µm
Width 90 µm
Operculum on one pole
Pale grey to greenish colour
Snails live on wet pasture, which can be drained or fenced off. Anthelmintic treatment of infected sheep has not been very successful.