Sparganosis

Sparganosis is maintained in nature primarily by contamination of natural or artificial bodies of water (lagoons, marshes, lakes, and others) with faeces from cats and dogs and infected with Spirometra spp. Secondary and intermediate hosts are aquatic crustaceans and other aquatic animals that ingest them, such as frogs. Then various mammal and bird species become infected by feeding on parasitized frogs or snakes.

The infection rate in humans is low, compared to the rate in other animals. Humans acquire sparganosis mainly by ingesting larvae contained in raw or undercooked meat of animals infected with spargana, such as amphibians, reptiles, birds, and wild mammals. Another mode of infection, also by larval transfer, is by contact. In Vietnam and Thailand, frog muscles are applied as poultices. This custom is responsible for ocular sparganosis. It is also probable that humans can acquire sparganosis via drinking-water by ingesting copepods infected with procercoids (first larvae).

Humans are an accidental host and do not usually play any role in the life cycle of the parasite. However, under ecologic conditions in some regions of central Africa, it is suspected that humans act as an intermediate host. In this region, hyenas are the definitive hosts of Spirometra, and humans are apparently the only host infected with Spargana. In these circumstances, the infection cycle is maintained as a result of the tribal custom of letting hyenas devour human corpses.

Sparganosis is found throughout the world, but human infection is not common. Just over 450 cases are known, mostly from Japan, China, Korea, and Southeast Asia.