CYSTICERCUS OVIS INFESTATION

(SHEEP MEASELS, SHEEP BLADDER WORM)

Life Cycle
Cysticercus ovis is the larval stage of Taenia ovis, a tapeworm found in the intestines of dogs and wild carnivores. Its development is similar to that of Taenia saginata. However, in the case of Taenia ovis, the definitive hosts are sheep. The cysts are found in the heart, diaphragm, masseters and the skeletal musculature of sheep. They are fully developed from 7 to 10 weeks after the ingestion of the ova. The rapid degeneration of cysts commence almost immediately after the cysts reach maximum development. When degenerated, the cysts appears as a caseous nodule in the musculature.

Antemortem findings
Usually no clinical signs are recognized.

Postmortem findings

1. The cysts are oval, measure 9 mm x 5 mm when fully developed and are most common in the heart, the masseters, the diaphragm and the skeletal musculature.
2. In older animals the cysts degenerate and calcify.
3. The degenerated cysts appears as greenish yellow caseous nodules with calcification often present.

(From : MANUAL ON MEAT INSPECTION FOR DEVELOPING COUNTRIES – FAO ANIMAL PRODUCTION AND HEALTH PAPER – ROME 1994 p 281)

Evaluation

1. Acute mild infestations with viable cysts : May be frozen at -18°C for three (3) days (as for bovine)
2. If one or more viable cysticerci are found on the majority of cut surfaces the carcass must be condemned. During the secondary meat inspection the triceps brachi and diaphragm need to be incised.
3. Carcasses with chronic degenerated calcified cysts should be condemned. These tend to present themselves as greenish-yellow caseous (at times calcified) nodules.

Prevention
Producers are encouraged to ensure regular de-worming of all dogs with a broad spectrum anti-helmintic. This is especially important in areas with working dogs in close contact with sheep. Farming conditions in the RSA suggest that wild carnivores are not an important vector in the transmission.