Bladder worm (Cysticercus tenuicollis) appears as cysts in the liver or loosely attached to the surface of other organs. Heavy infections of bladder worm in the liver can appear like liver fluke disease (fasciolosis).
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.
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 pass out in tapeworm segments in the dog’s faeces. If these are on pasture, they can be eaten by sheep in which larvae develop and migrate from the gut 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 carcasses that contain viable cysts that develop into tapeworms in the dog’s small intestine.
No treatment for cysts in sheep is available; control is based on breaking the life cycle. Specifically, this means preventing dogs from eating sheep carcasses, meat or organs. Freezing or cooking of meat and viscera may not reliably kill all cysts.
Dogs in sheep areas should be regularly treated for tapeworm.
These parasites have two names because the cyst stage was named before it was known to be a stage of the life cycle of Taenia hydatigena.
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, also occurs in dogs, with the intermediate stage affecting sheep and sometimes humans.
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