Flukes: Trematoda

Physical characteristics: Adult Fasciola hepatica (abbreviated to F. hepatica) are a little more than 1 inch (3 centimeters) long and three-eighths of an inch (1 centimeter) wide. They have a spiny outer covering. The front end has a mouth sucker and a cone-shaped tip, and the rear end is tapered. The sucker on the fluke's lower surface is larger than the mouth sucker.

Geographic range: F. hepatica live all over the world but mainly in Europe, Mexico, and Central America.

Habitat: F. hepatica live in swampy freshwater areas inhabited by snails. Snails are their sole intermediate hosts. The primary hosts include grazing mammals such as sheep, cattle, and horses; farm animals such as hogs; pets such as dogs, cats, and rabbits; and humans.

Diet: F. hepatica feed on the lining of the ducts, or tubes, in the liver, causing hardening of the ducts.

Behavior and reproduction: The eggs of Fasciola hepatica, which are deposited in the environment in the primary host's feces, hatch in Fasciola hepatica feed on the lining of the ducts, or tubes, in the liver, causing hardening of the ducts. (Illustration by Bruce Worden. Reproduced by permission.) freshwater areas, usually within about ten days, longer if temperatures are cool. These flukes have been known to survive in particularly cold water for several years. The embryos develop into larvae, which quickly swim to and penetrate the soft tissue of snails. The larvae produce more larvae, which transform. Larvae in their final stage live in the snails for four to eight weeks, then exit and swim to plants lying just below the water line. Passing plant-eating animals become infected when they eat the plants, often grass. Humans typically become infected by drinking water containing flukes or by eating greens such as watercress. The flukes travel to the abdominal cavity in the first twenty-four hours, then to the liver over the next few days. Within six to eight weeks, the flukes reach the liver ducts, where they mature and lay eggs. The eggs are then carried to the intestine and pass into the feces. The flukes sometimes spread to the lungs as well as the liver.

Fasciola hepatica and people: Humans infected with F. hepatica may have symptoms ranging from skin inflammation to pneumonia. Fluke infection can result in massive bleeding in horses, a reduction of milk production in dairy cattle, and death in sheep.

Conservation status: Fasciola hepatica are not threatened or endangered. ∎