|PARASITES - Platyhelminthes |
Echinococcus granulosus is the multicellular parasite that causes hydatid cyst disease. Adults can live in the intestinal tract of carnivorous animals like dogs where they shed their ova in the animal's feces. Human infection may result from ingestion of these ova. This can occur when ova get on a person's hands from petting an infected dog and fingers are subsequently put into the mouth without adequate hand washing. Larva, which develop from the ova, may lodge in the host's liver. Here they mature into a hydatid cyst, a fluid-filled sac which may eventually contain up to 4 gallons of fluid. Inside the cyst, buds form and grow into brood capsules where many immature scolices develop ("hydatid sand"). Three forms of Echinococcus are shown: adult, ova and hydatid sand. The adult is found in the intestine of an infected animal while the ova are shed in the animal's feces. Hydatid sand is found in an infected human, most frequently in the liver or lungs. Note that the ova of Echinococcus are indistinguishable from Taenia ova.
Symptoms of Echinococcus depend on the location of the cyst. Diagnosis is accomplished by serology or skin testing. Because an adult Echinococcus is flat, it is in the phylum Platyhelminthes . Echinococcus is a member of the class Cestoda (tapeworms). Cestodes lack a digestive tract of their own. |
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