a. Sheep Liver Fluke. This parasite, Fasciola hepatica, is common in the
sheep-raising areas of the world.
(1) The adult is a fleshy, leaf-shaped, hermaphroditic flatworm. It is about
30 millimeters long by 13 millimeters wide. The worm lays immature eggs which are
passed in the feces of the host, an infected animal. The eggs must reach the water to
mature and hatch. When the eggs hatch, they release a miracidium (a ciliated larval
form). The miracidium invades some varieties of snails, the snails being the
intermediate host. In the snail, the miracidium matures into a cercaria (a tailed larva).
The cercaria leaves the snail, is free-swimming for a short time, and then encysts in the
water or on aquatic vegetation. If it is kept moist, the cyst remains alive for a long time.
(2) Man becomes infected by drinking cyst-infected water or eating cyst-
infected vegetation. The ingested cyst dissolves in the intestines, releasing the larva.
The larva migrates through the intestinal wall and into the liver and bile ducts, where it
(3) The incidence of liver fluke disease in man is on the increase in cattle
and sheep raising areas. Epidemics of watercress-borne liver fluke disease have
occurred in Europe and South America.
b. Chinese Liver Fluke. Also called Clonorchis sinensis, this parasite occurs
primarily in Japan, Korea, and most of China.
(1) The adult worm is flabby, transparent, and spatual-shaped. It is 10 to 25
millimeters long and 3 to 5 millimeters wide. Like the sheep fluke, it lays immature eggs
which must reach water to mature and hatch. When the eggs hatch, the ciliated larva is
released. This larva invades a snail, not the same genre of snails as the sheep liver
fluke, and matures into a tailed larva. The tailed larva (the cercaria) leaves the snail
and finally encysts on or in various species of freshwater fish.
(2) Humans or other animals contract Chinese liver fluke disease by eating
raw, cyst-infected fish.
c. Signs and Symptoms. From the time they are infected, most people are
permanently free of symptoms and have few worms. People with a heavy infection will
experience these signs/symptoms.
(1) Sheep liver fluke. In the early stages of the disease, there is fever, pain
over the liver, diarrhea, loss of weight, and an increase in the number of certain white
blood cells, eosinophils. These symptoms are caused by the damage done to the liver
by the young flukes which are actually feeding on the liver tissue.