Echinostomes in humans

Abstract

A total of 20 species belonging to nine genera of Echinostomatidae are known to cause human infections around the world. They constitute an important group of food-borne trematodes of public health importance chiefly in the Southeast Asia and Far East. The largest genus is Echinostoma (seven species), followed by Echinochasmus (five species) and others (1–2 species for each genus), i.e., Acanthoparyphium, Artyfechinostomum, Echinoparyphium, Episthmium, Himasthla, Hypoderaeum, and Isthmiophora. Various types of food animals, including freshwater fish, brackish water fish, freshwater snails, brackish water snails (gastropods and bivalves), and amphibians are the sources of human infection. The pathogenicity and host-parasite relationships have been studied extensively in several species, including Echinostoma hortense (human-infecting species) and Echinostoma trivolvis and Echinostoma caproni (animal-infecting species). Mechanical damages by the worms and toxic effects by their metabolites seem to be important factors in the pathogenesis of human echinostomiasis. Mucosal ulcerations and bleeding at the upper part of the duodenum or at the distal part of the stomach are occasionally encountered in gastroduodenal endoscopy of human E. hortense infections. However, clinical importance of each echinostome species, as well as mucosal defense mechanisms of different hosts, is yet poorly understood. Diagnosis of echinostomiasis can be done by recovery of eggs in the feces, but specific diagnosis is difficult because of morphological similarity of eggs. Praziquantel has been proved to be effective against echinostomiasis. Epidemiological surveys and detection of human infections are required for better understanding of the geographical distribution and endemicity of each echinostome species.