Clinical, pathological and epidemiological findings in three outbreaks of ovine protozoan myeloencephalitis

Ovine protozoan myeloencephalitis is a disease of sheep associated with the apicomplexan protozoan Sarcocystis tenella. This paper describes the clini cal, pathological and epidemiological findings in three affected flocks fro m a well-defined geographical area. Clinical signs were restricted to sheep under one year old in their first winter and were first observed at least 42 days after they had been moved off the hill grazing areas to low ground pasture, or after they were given conserved forage. The findings are discus sed in relation to the timescale of the life cycle of S tenella and it is s uggested that clinical disease was precipitated by the change from a low le vel of exposure to infection on the hill to a high level of exposure throug h contaminated pasture or forage. Possible preventive strategies are discus sed.