Echinococcus granulosus

This article is about the tapeworm. For the infection, see echinococcosis.

Echinococcus granulosus
Echinococcus granulosus protoscolex
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Platyhelminthes
Class: Cestoda
Order: Cyclophyllidea
Family: Taeniidae
Genus: Echinococcus
Species:
E. granulosus
Binomial name
Echinococcus granulosus
Batsch, 1786

Echinococcus granulosus, also called the hydatid worm or dog tapeworm, is a cyclophyllid cestode that dwells in the small intestine of canids as an adult, but which has important intermediate hosts such as livestock and humans, where it causes cystic echinococcosis, also known as hydatid disease. The adult tapeworm ranges in length from 3 mm to 6 mm and has three proglottids ("segments") when intact—an immature proglottid, mature proglottid and a gravid proglottid.[1] The average number of eggs per gravid proglottid is 823. Like all cyclophyllideans, E. granulosus has four suckers on its scolex ("head"), and E. granulosus also has a rostellum with hooks. Several strains of E. granulosus have been identified, and all but two are noted to be infective in humans.[2]

The lifecycle of E. granulosus involves dogs and wild carnivores as a definitive host for the adult tapeworm.[3] Definitive hosts are where parasites reach maturity and reproduce. Wild or domesticated ungulates, such as sheep, serve as an intermediate host.[3] Transitions between life stages occur in intermediate hosts. The larval stage results in the formation of echinococcal cysts in intermediate hosts.[3] Echinococcal cysts are slow growing,[3] but can cause clinical symptoms in humans and be life-threatening.[4] Cysts may not initially cause symptoms, in some cases for many years.[3] Symptoms developed depend on location of the cyst, but most occur in the liver, lungs, or both.[4]

Echinococcus granulosus was first documented in Alaska but is distributed worldwide. It is especially prevalent in parts of Eurasia, north and east Africa, Australia, and South America.[4] Communities that practice sheep farming experience the highest risk to humans,[4] but wild animals can also serve as an avenue for transmission. For example, dingoes serve as a definitive host before larvae infect sheep in the mainland of Australia.[4] Sled dogs may expose moose or reindeer to E. granulosus in parts of North America and Eurasia.[4]

  1. ^ Pedro-Pons, Agustín (1968). Patología y Clínica Médicas (in Spanish). Vol. 6 (3rd ed.). Barcelona: Salvat. p. 955. ISBN 84-345-1106-1.
  2. ^ Eckert J, Deplazes P (January 2004). "Biological, epidemiological, and clinical aspects of echinococcosis, a zoonosis of increasing concern". Clin. Microbiol. Rev. 17 (1): 107–35. doi:10.1128/cmr.17.1.107-135.2004. PMC 321468. PMID 14726458.
  3. ^ a b c d e Cite error: The named reference Moro09 was invoked but never defined (see the help page).
  4. ^ a b c d e f McManus DP, Zhang W, Li J, Bartley PB (October 2003). "Echinococcosis". Lancet. 362 (9392): 1295–304. doi:10.1016/S0140-6736(03)14573-4. PMID 14575976. S2CID 208792285.