Fascioloides magna: Giant or large American fluke

General Description: Thick, flesh-coloured oval flukes with a rounded posterior end. They are 23 to 100mm long, 11 to 26mm wide and 2 to 4.5mm thick.

Life Cycle: Indirect. Similar to Fasciola hepatica. Adults are found in deer. Eggs hatch after 4 or more weeks. Prepatent period is about 3-5 months.

Location: Liver.

Geographical Distribution: North America, particularly the northern United States and Canada.

Significance: The large American fluke is a serious problem in the sheep since relatively few parasites may kill an animal. The threat is greater where deer and sheep share pasture.

Effect on Host: Fascioloides flukes are large and migrate extensively through the liver and other organs, causing tracts of tissue damage. Bleeding occurs and scar tissue forms. Liver function is often disrupted significantly and frequently results in death. Weakness and death may be the only apparent sign.

Diagnostic Information: Eggs resemble those of F. hepatica; eggs do not usually appear in faeces of sheep. Tracts of haemorrhage are seen in the liver at slaughter. Finding parasites at necropsy is necessary for definite diagnosis.

Control: Avoid grazing of sheep in areas where deer feed, since these wild ruminants are a reservoir of Fascioloides magna. Snails should be controlled by chemical treatment of pastures where they exist. Anthelmintics have not been expensively investigated for Fascioloides infections.

F. magna migratory tracts on rumen and diaphragm		Liver from a deer infected with F.magna fibrous cysts		Typical hepatic capsule in deer liver (2 flukes/capsule)