Types of Trematoda

Trematoda are flukes, a class of Platyhelminthes that are intestinal parasites found in humans and other animals. Trematoda cause infections resulting from ingesting inadequately cooked fish, crustaceans and vegetation containing their larvae or swimming in contaminated water. Trematoda are flatworms with a thick outer cuticle and one or more suckers or hooks used for attaching themselves to host tissue. Anyone traveling outside the U.S. should educate themselves about flukes.

Blood Flukes

• Blood flukes live primarily in intestinal blood vessels of marine life found in Southeast Asia, North Africa and other tropical regions. Flukes produce hundreds of thousands of eggs, causing its host's blood vessels to burst open. Blood and eggs leak into the intestine of the host where they expel with feces. Ingesting larvae is where health problems begin.

Tematoda Host

• Once trematoda eggs enter water systems they become larvae that swim to find a host, typically snails. A snail is an intermediate host where flukes reproduce asexually, resulting in new worms that enter the water system. Humans swimming in infested waters of underdeveloped countries commonly contract flukes. Flukes bore through human skin and eat their way into blood vessels where they travel to the heart lungs and intestine. Once inside an organ, the flukes live as adult worms, making humans very ill.

Human Liver Fluke

• Certain freshwater fish found in Asia and the south Pacific, including China, Korea, Vietnam, Taiwan, Japan, ingest the human liver fluke. Stone moroko fish and grass carp are the main sources of liver fluke infection in humans. Any fish-eating vertebrate is a potential host for this deadly fluke.

Effects on Humans

• Humans infected with flukes become weak and often die, either as a direct result of flukes or by contracting other diseases during their weakened state. As of 2011, only two types of blood flukes exist in U.S. lakes and streams. Primary hosts in the U.S. are fish and water birds. As of yet, flukes in the U.S. have not evolved into human parasites and cannot live in the human body, but not for a lack of trying. Flukes cause a condition known as swimmers itch when they try to burrow through the skin.

Lung Fluke

• The lung fluke lives in Japan, Korea, China, The Philippines, Indonesia, parts of Africa and South America. This fluke inhabits crabs and crayfish, then are ingested by humans who become infected. Once inside the lungs, the parasite encases itself in fibrous tissue, forming a capsule. A lung infection caused by a fluke resembles tuberculosis.