This parasite has two names because the cyst stage was named before it was known to be a stage of the life cycle of Taenia hydatigena. The life cycle has two hosts: the definitive host—usually the domestic dog, and also the dingo; and the intermediate host—sheep, goats, cattle and pigs.
Bladder worm (Cysticercus tenuicollis) appear as cysts in the liver or loosely attached by a long thin neck to the surface of other organs. Heavy infections of bladder worm in the liver can appear like liver fluke disease (fasciolosis).
The tapeworm stage (Taenia hydatigena) occurs in the small intestine of the dog, with the tapeworm itself being up to three metres long. The adults produce eggs that are contained within the tapeworm segments, which are passed out in the dog’s faeces. The segments burst releasing the eggs. If these are on pasture, they can be eaten by sheep or goats. The larvae continue to develop in the gut of the sheep or goat and then migrate into the liver or onto the surface of various organs where large cysts, up to 60 mm long, can form.
The cycle continues when dogs eat sheep or goat carcasses that contain viable cysts that develop into tapeworms in the dog’s small intestine.
No treatment for cysts in sheep or goats is available; control is based on breaking the life cycle. Specifically, this means preventing dogs from eating infected carcasses, meat or organs. Freezing or cooking meat and viscera may not reliably kill all cysts.
Dogs in sheep or goat areas should be regularly treated for tapeworm.
Despite the name—Taenia hydatigena—they do not cause hydatid disease and cannot infect humans. They are also called ‘false hydatid’.
Other tapeworms in dogs: Taenia pisiformis, T. serialis and Dipylidium caninum are common tapeworms of dogs, foxes and dingoes and should be differentiated from T. ovis (sheep measles) and T. hydatigena. The intermediate hosts of T. pisiformis and T. serialis are the rabbit and hare. The flea and possibly the biting louse are the intermediate hosts for D. caninum.
The hydatid tapeworm, Echinococcus granulosus, is a tiny tapeworm 4–6 mm long that also occurs in dogs, with the intermediate stage affecting sheep and goats and sometimes humans.
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Roundworms
Tapeworms
Flukes
Other occasional parasites of sheep and goats
