Sheep measles, otherwise known as cysticercosis, are small cysts found in the meat of sheep and goats. The consequence of these "measles" is partial or whole-carcass condemnation at the processing plant.
The cysts are found throughout the meat. Only a small portion are on or near the surface. Cysts are most easily seen in the diaphragm, heart, jaw muscles, and tongue. They are not known to pose a human health risk.
So where do these cysts come from?
From man’s best friends -- dogs! Sheep measles are caused by the tapeworm Taenia Ovis. The definitive host for this tapeworm is the dog, meaning the adult form of the worm lives in the dog’s digestive tract. There it grows and reproduces to the point that one dog can shed up to 250,000 eggs per day!
Like many internal parasites, this worm then goes through a larval form in an intermediate host – sheep. The sheep graze contaminated pastures or feed, ingest the eggs, which hatch into larva and migrate through the lamb’s body, eventually becoming encysted in the skeletal and heart muscle.
So, what can a producer do to prevent this life cycle?
Generally, tapeworms do not cause clinical illness in dogs (or sheep), so a healthy-appearing dog does not mean it doesn’t have tapeworms. Guardian dogs and herding dogs should be on a deworming program for tapeworms.
Tapeworms are the hardy sort and the over-the-counter dewormers that work on other worms are NOT effective against tapeworms. The only readily available and effective treatment for tapeworms is Praziquantel.
The next step a producer can take to reduce the risk of cysticercosis is to not feed dogs raw sheep meat. Controlling scavenging of sheep carcasses by domestic dogs, as well as the wild canids in the area is also necessary. Producers should restrict access of other dogs to their property, unless the dogs have been dewormed for tapeworms.
Prevention of the tapeworm in the dog is key to preventing sheep measles. There is no treatment for the larval form in sheep.
Sheep Measles: A Profit Drain for Producers (ASI)
Stop the life cycle of sheep measles (ASI)
Sheep Measles and Bladder Worm brochure (PDF)
Sheep Measles presentation at 2007 annual ASI meeting (PDF)