Larval Tapeworm Life Cycle: Hydatids, Beef Measles and Bladder Worm (predator-prey)

These are indirect life cycles with cattle as intermediate (prey) hosts in which the larval tapeworms develop, and the final host is a predator such as a dog for hydatid worms (Echinococcus granluosus)(Figure 1), or a human for beef measles (Taenia saginata, or Cysticercus bovis) and bladder worm (Taenia hydatigena)(Figure 2).

Note:

• Hydatid worms are regularly reported from cattle processing plants and are linked to reduced animal weight gains.
• Beef measles is uncommon in Australia but is of economic importance because visible cysts cause downgrading of expensive commercial cuts of meat during meat inspection.
• Bladder worm has a low incidence of infection in cattle in Australia, and infected animals are little affected.

Hydatid larval tapeworm lifecycle

(Echinococcus granulosus)

Beef measles and bladder worm larval tapeworm lifecycle

(Taenia saginata or Cysticercus bovis and Taenia hydatigena)

Intermediate (prey) host stage: cattle

Cattle become infected by ingesting vegetation contaminated with mature tapeworm segments containing eggs, which were passed by the dog or human host.

• In the small intestine of cattle, larval tapeworms penetrate the gut wall and are carried in the blood to their preferred attachment sites, e.g. liver and lungs (hydatids), striated and smooth muscles (beef measles), or the peritoneum (bladder worm).
• Once there they further develop, grow in size and form cysts.
  • Accidental ingestion of hydatid eggs by humans can lead to cysts developing in various organs causing hydatid disease (Figure 1).

Final (predator) host stage: dog or man

Man becomes infected with hydatids and beef measles by eating raw or undercooked beef. Hydatids can be transmitted to humans by many intermediate hosts including cattle, as well as by ingesting eggs released in dog faeces, which stick to the dog’s coat and can then be transmitted to humans by patting the dog.

Dogs are infected with bladder worm if allowed to scavenge, or if they are fed infected carcass meat or organs.

• Adult tapeworms live in the small intestine of either man or dog.
• Mature segments containing eggs are shed from the tapeworm and exit the host in the faeces.
• Segments in the dung burst, releasing eggs.
• Eggs can survive for days to months in the environment.