Echinostoma is an important genus

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 that includes many parasites

Parasitism

Parasitism is a type of symbiotic relationship between organisms of different species where one organism, the parasite, benefits at the expense of the other, the host. Traditionally parasite referred to organisms with lifestages that needed more than one host . These are now called macroparasites...

.

Human echinostomiasis is an intestinal parasitic disease caused by one of at least sixteen trematode flukes from the genus Echinostoma. Found largely in southeast Asia

Asia

Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...

 and the Far East, mainly in cosmopolitan areas. It has extensive vitelline glands for egg yolk production and tandem, oval testes. Echinostomiasis is transmitted through the ingestion of one of several possible intermediate hosts, which could include snail

Snail

Snail is a common name applied to most of the members of the molluscan class Gastropoda that have coiled shells in the adult stage. When the word is used in its most general sense, it includes sea snails, land snails and freshwater snails. The word snail without any qualifier is however more often...

s or other mollusks, certain freshwater fish, crustacean

Crustacean

Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...

s or amphibian

Amphibian

Amphibians , are a class of vertebrate animals including animals such as toads, frogs, caecilians, and salamanders. They are characterized as non-amniote ectothermic tetrapods...

s. These flukes are of moderate size, about 2 mm, and are distinguished by an oral sucker surrounded by a characteristic collar of spines.

Adults are in the small intestine

Intestine

In human anatomy, the intestine is the segment of the alimentary canal extending from the pyloric sphincter of the stomach to the anus and, in humans and other mammals, consists of two segments, the small intestine and the large intestine...

s of vertebrate definitive hosts. Eggs are released through the feces and embryonated. The egg becomes a miracidium

Miracidium

Trematodes are small parasitic flatworms that use vertebrates as their definitive host, and molluscs as their intermediate host. In order to accomplish this, they have several varied lifecyle stages....

 with an operculum, which penetrates a snail, the first intermediate host

Intermediate host

A secondary host or intermediate host is a host that harbors the parasite only for a short transition period, during which some developmental stage is completed. For trypanosomes, the cause of sleeping sickness, humans are the primary host, while the tsetse fly is the secondary host...

. Upon penetration, it becomes a mother sporocyst

Sporocyst

Sporocyst is a common name of a lifecycle stage in two unrelated groups of species:*Apicomplexa parasites: see Apicomplexa lifecycle stages*Trematode flatworms: see Trematode lifecycle stages...

, producing many mother rediae. Each of these mother redia produce many daughter rediae, which each produce many free-swimming cercariae. Each of these cercaria encysts in a freshwater mollusc, the second intermediate host, becoming a metacercaria. These mollusc are eaten by a vertebrate, the definitive host.

Upon infection of the human host

Host (biology)

In biology, a host is an organism that harbors a parasite, or a mutual or commensal symbiont, typically providing nourishment and shelter. In botany, a host plant is one that supplies food resources and substrate for certain insects or other fauna...

, the worms aggregate in the small intestine where they may cause no symptoms, mild symptoms, or severe symptoms in rare cases, depending on the number of worms present. Diarrhea

Diarrhea

Diarrhea , also spelled diarrhoea, is the condition of having three or more loose or liquid bowel movements per day. It is a common cause of death in developing countries and the second most common cause of infant deaths worldwide. The loss of fluids through diarrhea can cause dehydration and...

 is a result of heavy infections. Effective drugs for treatment do exist, but the disease still remains a problem in endemic areas.

Prevention and control is possible through measures such as health education

Health education

Health education is the profession of educating people about health. Areas within this profession encompass environmental health, physical health, social health, emotional health, intellectual health, and spiritual health...

; altered eating habits to exclude ingestion of raw fish, mollusks and other sources of the disease; and removing of wastewater

Wastewater

Wastewater is any water that has been adversely affected in quality by anthropogenic influence. It comprises liquid waste discharged by domestic residences, commercial properties, industry, and/or agriculture and can encompass a wide range of potential contaminants and concentrations...

and industrial discharge that may be home to the parasite.