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Endoparasites - Hydactic Cyst

Hydatid cyst: Intermediary stage of Echinococcus granulosus.

General Description: Echinococcus granulosus is a small tapeworm for which dogs and related carnivores are principal hosts. This tapeworm has only 3 to 4 proglottides and is 2 to 5cm long. Most mammals including sheep, cattle, pigs, and man can serve as intermediate hosts of the hydatid cyst form.

Life Cycle: Indirect cestode life cycle. Adults in dogs pass gravid proglottides with eggs in faeces. When ingested by mammals (such as sheep), these eggs hatch. The hexacanths develop to metacestodes, penetrate the gut wall, and enter the blood stream, which carries them to various organs, typically the liver and lungs, where bladder worms or hydatid cysts develop. These are large cysts filled with fluid and several tapeworm heads. Principal hosts are infected by eating organs containing cysts.

Location: Tapeworms live in the small intestine of the principal host. Hydatid cysts can be in any organ of the intermediate host. Predilection sites are lungs and liver.

Geographical Distribution: Worldwide.

Significance: Feeding uncooked viscera of intermediate hosts to dogs, dingoes, or coyotes may cause infection. Hydatid disease in sheep is not usually a problem, but infected organs are condemned at slaughter. Infections in farm animals provide a reserve to keep hydatid tapeworm infection in dogs. In man it is a very serious problem.

Effect on Intermediate Host: Pathogenicity depends on the severity of the infection and location of the cyst.

Diagnostic Information: Usually diagnosis is not made until viscera are examined at slaughter, when hydatid cysts may be seen in tissue. Infected dogs pass Taenia-type eggs in faeces.

Control: Treat dogs regularly for tapeworms. Dogs should not be fed uncooked viscera.

Scolex – in intestine of dog   Hydatid cyst in lung   Hydatid cysts – sheep liver


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