Sheep oesophagus infected with Sarcocystis
The white, blister-like formations on the outside of the oesophagus are tissue cyst forms of Sarcocystis and are called sarcocysts. Each Sarcocyst contains a large number of bradyzoites - the slow growing form of the parasite and is infective for the next host in the cycle - a dog or a cat who are the final hosts for the parasite. The presence of these tissue cysts is not associated with disease in the sheep, their prime importance being when they occur in the body musculature leading to condemnation at meat inspection.The species of Sarcocystis responsible for the cysts in this photo is either S.tenella (sheep-dog cycle) or S.ovifelis (sheep-cat cycle).