This parasite has two names: the cyst stage, Cysticercus tenuicollis was named before it was known to be connected to the life cycle of the false hydatid tapeworm of dogs, Taenia hydatigena. Bladder worm does not cause hydatid disease and it does not infect humans.
Figure 1. Bladder worm Cysticercus tenuicollis larvae. Image courtesy of Constantin Constantinoiu
Taenia hydatigena in dogs is not to be confused with the hydatid tapeworm, Echinococcus granulosus that also occurs in dogs and produces cysts in cattle and most other warm-blooded animals (including humans).
Taenia saginata, the beef tapeworm of man, also produces cysts in cattle called beef measles.
Bladder worms appear as fluid filled sacs or cysts close to the liver surface or loosely attached to the mesentery of the peritoneum (the lining of the abdominal cavity). Usually single pendulous cysts are common but occasionally many cysts may cover both the visceral and parietal surfaces. Heavy infections of bladder worm in the liver can resemble liver fluke disease.
The incidence of infection in cattle is much lower than it is in sheep.
Figure 2. Bladder worm Cysticercus tenuicollis larvae attached to the peritoneum. Image courtesy of Constantin Constantinoiu
Adult tapeworms are located in the small intestine of dogs. The larval cysts in cattle are found in the peritoneal cavity.
Cattle are little affected.
This is an indirect predator/prey life cycle. The predator hosts are usually domestic dogs and dingoes, and the intermediate hosts for the cysts are usually sheep and goats, but also cattle and pigs.
The adult tapeworms in the small intestine of dogs produce eggs that are contained within the tapeworm segments, which, when passed out in the dog’s faeces burst open releasing the eggs containing a hexacanth (6 toothed) embryo. Cattle ingest these during grazing. The hexacanth embryo, once released in the gut of cattle, migrates through the gut wall and into the liver or onto the surface of various organs where large cysts, up to 60-85 mm in diameter, can form.
The cycle continues when dogs eat carcasses containing viable cysts. Once in the small intestine of the dog, cysts release the larval tapeworm which then develops into an adult tapeworm.
No treatment for cysts is available or necessary; control is based on breaking the life cycle. Specifically, by preventing dogs from eating infected carcasses. Freezing or cooking meat and viscera may not reliably kill all cysts. Dogs in endemic areas should be regularly treated for tapeworms, especially for the more important T. saginata and hydatids.