Monday, September 22, 2014

Flukes (Class Trematoda)

Flukeworms are mainly internal parasites of higher animals. Belonging to the Trematoda Class of Platyhelmithes, they range in length form a few millimeter to several centimeters. To adapt to a parasitic life, they have lost the soft, ciliated epidermis of the free-living flatworms, but they have developed a hard, outer cuticle, which protects them from the host body fluids and immune system. Most flukes have complex life cycle, involving several hosts, one of which is almost always a snail. A common one in some parts of the world is a Chinese liver fluke, whose life cycles involves three hosts. Flukes are serious disease-producers in man and domestic animals. The ones taking the greatest toll in human life belong to the genus Schistosoma.

Fluke's Life Cycle

A human being can pick up this parasitic organism by eating raw or undercooked fish, usually a carp or a trout, which contains larvae of the parasite. The immature fluke enter man's liver, living there and causing extensive damage and producing eggs, which leave the body with the feces. If some of the fecal material reaches a body of fresh water, such as a lake, the fluke egges hatch into larvae as some of them infect snails, reaching its liver, where they reproduce asexually into another larval stage called cercaria. A single infected snail may release as many as 200,000 cercarial larvae. This second larval stage leaves the snail and burrows into through the scales and skin of a fish. The cercarial larvae form cysts in the fish muscles. The cycle starts all over again when a human being consume raw fish. Thus, all three hosts (snail, fish, and man) are needed to complete a reproducing cycle of the fluke.

Below, schematic view of a parasitic fluke's life cycle

Below, a macrophotography of an adult flukeworm