Sheep ingest tapeworm eggs from the pasture, these eggs can survive on pasture for up to six months but most eggs are no longer viable at four months, length of egg survival is highly dependant on the environment.
The eggs if swallowed by a sheep, hatch in the intestine and the larvae migrate through the intestinal wall into the blood stream where they eventually lodge in muscle tissue (e.g. diaphragm, heart and skeletal muscle of sheep) where they develop.
Cysts become mature in around 35 days and remain alive for up to 90 days in muscle tissue. Some cysts have been found to survive up to 18 months. Once cysts die they become hard gritty and more easily detected at processing.
The viable cysts are highly infective and one viable cysts consumed by a dog is likely to result in infection. Therefore if dogs are fed or get access to untreated meat containing viable cysts a tapeworm will develop in the dog’s gut and mature in approximately 35 days. The tape worm is extremely fecund and can shed up to three segments a day, each segment containing around 60,000-80,000 eggs. The eggs are expelled when the dog defecates.