Fasciolopsis buski
Fasciolopsis buski is a parasite, a fluke that infects humans, pigs, dogs and rabbits in southern Asia. It is often called the giant intestinal fluke because it is one of the largest flukes to infect people—adult worms can be 75mm (about three inches) long and 20mm (nearly an inch) wide.
Though many of us are familiar with the term “liver fluke,” F. buski does not live in the liver: these large leaf-shaped worms inhabit the upper regions of the small intestine. When there are many worms, they are also found in lower areas of the intestine and in the stomach. Fasciolopsis buski is not found in other parts of the body.
Geographical distribution and life cycle
Fasciolopsis buski has a limited geographical distribution. It is found only in Bangladesh, Cambodia, China (in the central and southern regions), India, Indonesia, Laos, Malaysia, Pakistan, Taiwan, Thailand and Vietnam. Animal reservoirs (animals that also become infected and spread the parasite in the environment), and the use of untreated human feces for fertilizer make it difficult to prevent human infections.
In other parts of the world, the giant intestinal fluke does not occur, either because the climate does not support its survival there or because the necessary intermediate hosts (plant or animal hosts that do not host the parasite during its sexually reproductive stage) are absent. To understand why the parasite does not spread further geographically, it’s necessary to understand its complicated life cycle:
- An individual infected with F. buski passes thousands of microscopic eggs in the stool—each adult worm produces 25,000 eggs every day. Eggs passed or washed into a body of fresh water continue to develop.
- After about seven weeks, tiny parasitic organisms called “miracidia” emerge. To continue development, they require one of several species of aquatic snail. If the appropriate species is present, the miracidia enter snails and reproduce. If the right species of snail is absent, the miracidia die.
- Parasites exit the snails as “cercariae,” another stage in the life cycle of the giant intestinal fluke. Cercariae find water plants and encyst on them, building little protective envelopes around themselves.
- If the water plants with “metacercariae” are eaten raw by a suitable species of animal (human, pig, dog, rabbit), the worms can mature to adults in the intestine. In about three months, they will begin producing eggs, starting the life cycle over again.
Symptoms
When only a few worms are present in the intestine, there are likely to be few or no symptoms. Heavy infections are typically marked by abdominal pain, chronic diarrhea, and bowel obstruction. Abscesses sometimes develop and worms may be passed in the stool. Some people develop a serious allergic reaction to the worms. Heavy infections can be fatal.
Risk factors for infection
More than ten million people in southern Asia may have F. buski flukes residing in their intestines. To be at risk of F. buski infection, humans must:
- Have lived or traveled in a country where the fluke is present.
- Have eaten raw water plants (water chestnuts, bamboo shoots, water caltrop, morning glory and other water plants), peeled parts of these raw plants with the teeth, or consumed contaminated water containing infective metacercariae.
Read about other parasites and related subjects:
A Parasite in the Blood Supply
Sources:
Garcia, Lynn S. and David A. Bruckner. Diagnostic Medical Parasitology 3rd ed. Washington: ASM Press, 1997.
Leventhal, Ruth and Russell F. Cheadle. Medical Parasitology 5th ed. Philadelphia: F.A. Davis, 2002.
Schmidt, Gerald D. and Larry S. Roberts. Foundations of Parasitology 6th ed. Boston: McGraw Hill, 2000.
Rosemary Drisdelle - Rosemary Drisdelle has been published many times as a nonfiction writer and several times as a poet. Her first book, Parasites: Tales of ...
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