Phylum – Platyhelminthes
Class – Cestoda
Genus – Echinococcus
Species – E. granulosus
Echinococcosis is a parasitic disease caused by infection with tiny tapeworms of the genus Echinocococcus. Humans are accidental host, infection is caused with the ingestion of larval (egg) stage of Echinococcus granulosus, a tapeworm found in dogs (definitive host) and sheep, cattle, goats, and pigs (intermediate hosts). The parasite is transmitted to dogs when they ingest the organs of other animals that contain hydatid cysts. The cysts develop into adult tapeworms in the dog. Infected dogs shed tapeworm eggs in their feces which contaminate the ground. Sheep, cattle, goats, and pigs ingest tapeworm eggs in the contaminated ground.
Habitat and geographical distribution
Adult form of parasite resides in the intestine of dog, while larval form in liver, lungs of man.
The infection is distributed worldwide, but is specifically found in cattle-rearing countries, where dogs are able to ingest organs from infected animals.
Life cycle of E. granulosus
The adult Echinococcus granulosus (2—7 mm long) resides in the small intestine of the definitive host (dog). Gravid proglottids release eggs that are passed in the feces, and are immediately infectious. After ingestion by a suitable intermediate host, eggs hatch in the small intestine and release six-hooked oncospheres, that penetrate the intestinal wall and migrate through the circulatory system into various organs, especially the liver and lungs. In these organs, the oncosphere develops into a thick-walled hydatid cyst that enlarges gradually, producing protoscolices and daughter cysts that fills the cyst interior. The definitive host becomes infected by ingesting the cyst-containing organs of the infected intermediate host. After ingestion, the protoscolices evaginate, attach to the intestinal mucosa , and develop into adult stages in 32 to 80 days.
Humans are aberrant/accidental intermediate hosts, and become infected by ingesting eggs. Oncospheres are released in the intestine, and hydatid cysts develop in a variety of organs. If cysts rupture, the liberated protoscolices may create secondary cysts in other sites within the body (secondary echinococcosis).
Clinical manifestation of echinococcosis
Persons with cystic echinococcosis often remain asymptomatic until hydatid cysts containing the larval parasites grow large enough to cause discomfort, pain, nausea, and vomiting.
The cysts grow over the course of several years before reaching maturity and the rate at which symptoms appear typically depends on the location of the cyst.
The cysts are mainly found in the liver and lungs but can also appear in the spleen, kidneys, heart, bone, and central nervous system, including the brain and eyes.
Cyst rupture is most frequently caused by trauma and may cause mild to severe anaphylactic (allergic) reactions, even death, as a result of the release of cystic fluid.
the presence of a cyst-like mass in a person with a history of exposure to sheepdogs in an area where E. granulosus is endemic suggests a diagnosis of cystic echinococcosis.
Imaging techniques, such as CT scans, ultrasonography, and MRIs, are used to detect cysts. After a cyst has been detected, serologic tests (IHA, ELISA) may be used to confirm the diagnosis.
Treatment, prevention and control
- surgery remains the most effective treatment to remove the cyst and can lead to a complete cure. Some cysts are not causing any symptoms and are inactive; those cysts often go away without any treatment.
- Prevent dogs from feeding on the carcasses of infected sheep.
- Control stray dog populations.
- Restrict home slaughter of sheep and other livestock.
- Do not consume any food or water that may have been contaminated by fecal matter from dogs.
- Wash your hands with soap and warm water after handling dogs, and before handling food.
- Teach children the importance of washing hands to prevent infection.