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. 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.

The lifecycle of E. granulosus involves dogs and wild carnivores as a definitive host for the adult tapeworm. Cysts may not initially cause symptoms, in some cases for many years. Humans can also be an intermediate host for E. granulosus, however this is uncommon and therefore humans are considered an aberrant intermediate host. Adult E. granulosus release eggs within the intestine which will be transported out of the body via feces. The cyst can cause pressure on surrounding tissue which may lead to abnormal organ function, spontaneous fracture of bones, and other neurological effects.

The frequency of offal feedings, the prevalence of the parasites within the offal, and the age of the intermediate host are factors that affect infection pressure within the definitive host.

Diagnosis

Diagnosis in the definitive host, the dog, may be done by post mortem examination of the small intestine, or with some difficulty ante mortem by purging with arecoline hydrobromate. Detection of antigens in feces by ELISA is currently the best available technique. The prevalence of Echinococcus granulosus was found to be 4.35% in a 2008 study in Bangalore, India, employing this coproantigen detection technique. Polymerase chain reaction (PCR) is also used to identify the parasite from DNA isolated from eggs or feces.

Treatment

If a human becomes infected there are a variety of methods for treatment. The most common treatment in the past years has been surgical removal of the hydatid cysts.

See also

  • Echinococcus multilocularis
  • Fasciola hepatica
  • Taenia solium

References

Further reading

  • Echinococcus from the US CDC
  • Echinococcus granulosus in the NCBI Taxonomy Browser