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Echinostoma is a genus of Trematoda (flukes), which can infect both humans and other . These intestinal trematoda 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 bivalvia or fish.
Methods for classifying Echinostoma species, such as the Echinostoma revolutum group, were devised by Kanev. 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.
Molecular methods, such as sequencing mitochondrial DNA and ribosomal DNA, are also used to distinguish between species of Echinostoma as an alternative to morphological classification methods.
Further confirmed species are E. lindoense Sandground & Bonne, 1940 and E. luisreyi Maldonado, Vieira & Lanfredi, 2003, these are not included in the phylogeny because of a lack of genetic material. Unconfirmed species are E. acuticauda, E. barbosai, E. chloephagae, E. echinatum, E. jurini, E. nudicaudatum, E. parvocirrus, E. pinnicaudatum, E. ralli, and E. rodriguesi.
The length and width of adult Echinostoma varies between species, but they tend to be approximately 2-10mm × 1-2mm in size.
Adult Echinostoma have two suckers: an anterior oral sucker and a ventral sucker. They also have a characteristic head collar with spines surrounding their oral sucker. The number of collar spines varies between Echinostoma species, but there are usually between 27 and 51. These spines can be arranged in one or two circles around the sucker, and their arrangement may be a characteristic feature of an Echinostoma species.
Echinostoma have a digestive system consisting of a pharynx, esophagus and an excretory pore.
Echinostoma are , and have both male and female reproductive organs. The testicle are found in the posterior part of the fluke's body, in the area furthest from the mouth. The ovary is also found in this location, close to the testes.
The (ova) of Echinostoma are operculate and vary in size, but are typically in the range of 80–135 × 55–80 μm.
Echinostoma species have low specificity for their definitive hosts, and can infection a variety of different species of animal, including , water bird, and humans. A definitive host which is infected with Echinostoma will shed unembryonated Echinostoma in their faeces. When the eggs are in contact with fresh water they may become embryonated, and will then hatch and release miracidia. The miracidia stage of Echinostoma is free-swimming, and actively penetrates the first intermediate snail host, which then becomes infected.
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. The cercariae are released from the snail host into water and are also free-swimming. The cercariae penetrate a second intermediate host, or they remain in the first intermediate host, where they form metacercariae. Definitive hosts become infected by eating secondary hosts which are infected with metacercariae. Once the metacercariae have been eaten, they excyst in the intestine of the definitive host where the parasite then develops into an adult.
Echinostoma are . A single adult individual has both male and female reproductive organs, and is capable of self-fertilization. Sexual reproduction of adult Echinostoma in the definitive host leads to the production of unembryonated eggs. The life cycle of Echinostoma is temperature dependent, and occurs quicker at higher temperatures. Echinostoma eggs can survive for about 5 months and still have the ability to hatch and develop into the next life cycle stage.
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.
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