Ovine myeloencephalitis-leukomyelomalacia associated with a Sarcocystis-like protozoan.

Bilateral pelvic limb paresis developed in 7 of 15 10-month-old Blueface Leicester ram lambs on a mixed enterprise farm in the North of England. Clinical signs were principally mild to severe paresis of the pelvic limbs. Two mildly affected lambs recovered. Multifocal spinal cord white matter edema and necrosis, glial nodules, and mild to moderate nonsuppurative encephalomyelitis were the principal findings in 3 severely paretic lambs examined histologically. Protozoan bodies (12.7-23.0 microns) that stained immunocytochemically for Sarcocystis epitopes were in spinal cord glial cells of 2 of 3 lambs. Protozoa did not react immunocytochemically with anti-Toxoplasma gondii or Neospora canium antisera. Serology indicated there was recent exposure to Sarcocystis spp. in some surviving lambs. These cases resembled those in previous reports of paresis due to an unidentified Sarcocystis-like protozoan in sheep (ovine protozoan myeloencephalitis) in the British Isles, the USA, France, Australia, and New Zealand.