Toxoplasma
Sheep and all vertebrates (including humans) are intermediate hosts. Cats are the final host. It is found in cooler climates. The coccidial cycle occurs in cats.

Ingesting sporulated oocysts from areas contaminated with cat faeces infects sheep. Parasites migrate throughout the body and lodge in any of several organs and may also pass to the foetus if the animal (or human) is pregnant. In the tissues they divide within cysts and cause focal lesions. Cats ingest cysts in sheep meat (or sporulated oocysts) to continue the cycle.

Toxoplasma can cause early or late abortion in ewes having their first lamb. Death of young lambs may also occur. These are microscopic protozoa and cysts. Sometimes white flecks are found on the placenta in infected animals. To confirm the diagnosis, send placenta and serum from unfed lambs to laboratory.

Sarcocystis (S tenella, S gigantia, S medusiformis) Sheep are the intermediate hosts. Dogs are the final host for one species (S. tenella), and cats for S. gigantia and S. medusiformis. The lifecycle is indirect. Sheep are infected by eating sporocysts in dog or cat faeces. These develop to a further stage (the equivalent of meronts) in walls of blood vessels and muscle. Dogs or cats eat muscle cysts where they pursue a coccidial cycle.

Appearance
S. tenella: microscopic muscle cysts, S. gigantia & S. medusiformis: large white cysts. Oocysts in the faeces of cats and dogs are microscopic.

Distribution
Cooler climates associated with dogs or cats.

Disease
Mostly not apparent, severely affected animals may be stunted or may abort.

Diagnosis
Cysts in muscle and often the oesophagus are seen at post mortem. Macrocysts in oesophagus of sheep.