Echinostoma revolutum

Echinostoma revolutum is the most widely distributed species of the known 20 Echinostomatidae species; it is found in Asia, Oceania, Europe, and the Americas.[3] In Asian countries the disease is endemic to humans. Outbreaks have been reported in North America after travellers returned from Kenya and Tanzania.[4]

The worms are leaflike, elongated, and an average of 8.8 mm long (8.0–9.5 mm) and 1.7 mm wide (1.2–2.1 mm). When first passed in the feces, they were pinkish red and coiled in a "c" or "e" shape. The eggs in uteri were an average of 105 μm long (97–117 μm) and 63 μm wide (61–65 μm).[1]

Cercariae of Echinostoma revolutum from snails

Infection of Echinostoma revolutum usually results from ingestion of raw snails or frogs that serve as an intermediate host. This parasite is predominantly found throughout North America. Two asexual generations occur in a snail or mollusc.[5] The first snail host is penetrated by a miracidium, producing a sporocyst. Many sporocysts are produced and mother rediae emerge. Mother rediae asexually reproduce daughter rediae, which also multiply. Each rediae then develop into a cercariae, which penetrates a second host. The second host could be another snail or a tadpole, in which development into metacercaria occurs. Cercariae typically find a snail host through chemotaxis. The cercariae are attracted to the slime of the snail, which contains small peptides. The first larval stage is the miracidium, and are found to be attracted to macrocmolecular glycoconjugates associated with a possible snail host. Environmental stimuli such as light and gravity can also be used to assist in searching for a host.

In Pursat Province, Cambodia, children eating undercooked snails or clams were identified as a possible source of infection in humans.[1]

Kelly, Cynthia (2009). "Echinostoma revolutum". Archived from the original on 13 August 2007. Retrieved 2017-02-17.