| Echinococcus | |
|---|---|
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Platyhelminthes |
| Class: | Cestoda |
| Order: | Cyclophyllidea |
| Family: | Taeniidae |
| Genus: | Echinococcus |
The genus Echinococcus includes six species of cyclophyllid tapeworms to date, of the family Taeniidae. Infection with Echinococcus results in hydatid disease, also known as echinococcosis.
Echinococcus is triploblastic, i.e.it has 3 layers- outermost ectoderm, middle mesoderm and inner endoderm. Anus is absent; incomplete digestive system. Body is covered by cuticle and is divided into scolex, short neck and 3-6 proglottids. Body is ribbon-like.
In humans, this causes a disease called echinococcosis. Latency can be up to 50 years, and is mostly found in South and Central America, the Middle East, China, and the West of the U.S.A. (e.g. Arizona, New Mexico and California).
Echinococcosis is a zoonosis; humans are dead-end hosts. The final hosts are predators - dogs, wolves, foxes, lions. The adult tapeworm lives in their intestine and delivers eggs that are excreted with the stool. The intermediate hosts are infected by ingesting eggs. Sheep, wild herbivores and rodents are the usual intermediate hosts, but humans can also be infected.
The egg hatches in the digestive system of the intermediate host, producing planula larva. It penetrates the intestinal wall and is carried by bloodstream to liver, brain, lung or another organ. It settles there and turns into a bladder-like structure called hydatid cyst. From the inner lining of its wall, protoscolices (i.e. scolices with invaginated tissue layers) bud and protrude into the fluid that is filling the cyst.
After the death of the normal intermediate host, its body can be eaten by carnivores suitable as final hosts. In their intestines, protoscolices turn inside out, attach and give rise to adult tapeworms, completing the life cycle.
In humans, the cysts persist and grow for years. They are regularly found in the liver (and every possible organ: spleen, kidney, bone, brain, tongue and skin) and are asymptomatic until their growing size produces symptoms or are accidentally discovered. Disruption of the cysts (spontaneous or iatrogenic e.g. liver biopsy) can be life threatening due to anaphylactic shock.
Cysts are detected with ultrasound or CT or other tests. Antibodies can be detected with CF (complement fixation), ELISA, and various methods.