Echinostoma is a genus of trematodes (flukes), which can infect both humans and other animals. These intestinal flukes have a three-host life cycle with snails or other aquatic organisms as intermediate hosts, and a variety of animals, including humans, as their definitive hosts.
Echinostoma infect the gastrointestinal tract of humans, and can cause a disease known as echinostomiasis. The parasites are spread when humans or animals eat infected raw or undercooked food, such as bivalve molluscs or fish. however, currently 16 species have been accepted as valid species with another 10 to be validated Echinostoma are difficult to classify based on morphology alone. Many species look alike and can be considered cryptic species (different lineages are considered to be the same species, due to high morphological similarity between them). Many species of Echinostoma have been re-classified several times. For example, the species now known as Echinostoma caproni, was previously known by a variety of names including E. liei, E. paraensei and E. togoensis. The Echinostoma species in this group are now classified according to their shared morphological and biological characteristics, such as the presence of 37 collar spines.
Species
Phylogeny of most known Echinostoma species based on the mitochondrial nad1 sequences:
Adult Echinostoma have two suckers: an anterior oral sucker and a ventral sucker. The number of collar spines varies between Echinostoma species, but there are usually between 27 and 51.
Geographic distribution
The genus Echinostoma has a global distribution. These parasites are particularly common in South East Asia, in countries such as South Korea and the Philippines. However, they are also found in some European countries,
Life cycle
Echinostoma have three hosts in their life cycle: a first intermediate host, a second intermediate host and a definitive host. Snail species such as Lymnaea spp. are common intermediate hosts for Echinostoma,
Echinostoma species have low specificity for their definitive hosts, and can infect a variety of different species of animal, including amphibians, aquatic birds, mammals and humans.
thumb|right|upright=1.4|alt=An illustrated life cycle of the Echinostoma parasite, beginning with the emergence of unembryonated eggs from an infected person, and ending with mature adults in a host. The life cycle is described in the adjacent text.|Life cycle of Echinostoma.
In the first intermediate host, the miracidium undergoes asexual reproduction for several weeks, which includes sporocyst formation, a few generations of rediae and the production of cercariae.
Echinostomiasis
Infection of humans with members of the family Echinostomatidae, including Echinostoma, can lead to a disease called echinostomiasis. E. revolutum, E. echinatum, E. malaynum and E. hortense are particularly common causes of Echinostoma infections in humans. A mild infection may not have any symptoms. If symptoms are present they can include abdominal pain, diarrhoea, tiredness and weight loss.
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Echinostomiasis can be controlled at the same time as other food-borne parasite infections, using existing control programmes. Interrupting the parasite's lifecycle by efficient diagnosis and subsequent treatment of infected individuals, and preventing reinfection, may help to control this disease. As echinostomiasis is acquired through the consumption of raw or undercooked infected food, cooking food thoroughly will prevent infection.<section end=prevention />