Fascioloides magna: Large liver fluke, large American fluke.

General Description: Adults are large and thick, as much as 10cm in length and 3cm. wide.

Life Cycle: Indirect, with snail as intermediate host. Eggs hatch in 4 or more weeks and must develop in snails for about 7 to 8 weeks before becoming infective for cattle. In cattle, a capsule is formed around the fluke which prevents passage of eggs. Fascioloides eggs are passed in the faeces of infected deer, the normal host. The prepatent period is 3 months.

Location: Liver.

Geographical Distribution: North America and Europe.

Significance: Cysts in livers cause condemnation at slaughter. Deer and elk are normal hosts. F. magna is not normally a parasite in cattle but infection occurs when cattle graze in the same areas as deer.

Effect on Host: When infection does exist in cattle, cysts that successfully isolate the worms are made by the host. The only damage may be obstruction of the liver, where cysts or capsules up to 4cm in diameter are formed around flukes.

Diagnostic Information: Encapsulated flukes do not pass eggs. Cysts may be noticed in liver at necropsy.

Control: Keep deer away from grazing areas. Elimination of snails is difficult, as is treatment of infected cattle because of the resistance of encysted flukes.

Comparative size immature vs mature F. magna in deer

Lesions on liver capsule		F.magna cysts in liver cattle