Echinococcus granulosus: Hydatid tapeworm.

General Description: A small tapeworm for which dogs and related carnivores are principal hosts. This tapeworm has only 3 to 4 proglottids and is 2 to 5cm long. Most mammals can serve as intermediate hosts, including cattle, sheep, pigs, and man.

Life Cycle: Indirect cestode life cycle. Adults in dogs pass gravid proglottids with eggs in faeces. When ingested by mammals (such as cattle) 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 cattle 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: Virtually no effect on cattle unless the cyst becomes very large. Adult worms in dogs are not significant.

Diagnostic Information: Usually diagnosis is not made until carcasses 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