Echinococcus granulosus: dogs and human hydatid disease
7-year-old Mastiff guarding a flock of sheep on an extensive farm in Castile and León. It has access to the remains of dead lambs and sheep. The family ask about hydatid disease after hearing of a case in the village.
Which statement is correct?
chevron_right Show answer and explanation
A. People are infected mainly by eating undercooked lamb meat or offal
The hydatid cyst in sheep infects only the definitive host (the dog). People are accidental intermediate hosts and become infected by ingesting eggs.
B. The dog harbours the adult worm in its intestine, usually without signs, and sheds eggs that infect people by the faecal–oral route
Correct. The dog is infected by eating hydatid cysts in sheep offal. The eggs contaminate the coat, soil, water and vegetables, and in people they form hydatid cysts, mainly in the liver and lungs.
C. The dog develops severe hepatic hydatid cysts and is the main animal affected
The dog is the definitive host: the adults are a few millimetres long, live in the intestine and rarely cause signs. Cysts form in intermediate hosts.
D. The eggs need weeks in the environment to become infective, so contact with the dog poses no risk
That applies to Toxocara. Echinococcus eggs are infective as soon as they are passed and very resistant in the environment; they can stick to the dog's coat.
lightbulb Key takeaway
Hydatid disease is still present in Spain, especially in areas of extensive sheep farming. The cycle is broken by preventing dogs from eating raw offal (proper disposal of carcasses and condemned viscera) and deworming them with praziquantel. Stress handwashing after handling at-risk dogs.
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Updated: October 31, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.