Atlas of livestock parasites
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Fascioloides magna (cattle)



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Fascioloides magna
Large liver fluke, large American fluke

General Description:
Adults are large and thick, as much as 10 cm in length and 3 cm 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 feces of infected deer, the normal host. The prepatent period is 3 months.


Geographical Distribution:

North America and Europe.

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 4 cm in diameter are formed around flukes.

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

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


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