Neospora caninum infection in three Labrador littermates.

: Neospora caninum is a recently identified protozoan parasite which was previously confused with Toxoplasma gondii. Neosporosis in puppies commonly causes signs referable to parasitic encephalomyelitis and myositis. The parasite was identified in tissues from 3 9-week-old Labrador littermates which showed signs of progressive hind limb hyperextension and paralysis. The diagnosis was confirmed, utilising a specific avidin-biotin immunohistochemical technique. Attempts to treat the pups with clindamycin were unsuccessful. One case was additionally treated with immunosuppressive doses of corticosteroids, but showed no improvement. Two pups were euthanased and necropsied. The predominant lesions were polymyositis and multifocal encephalomyelitis. Large clusters of tachyzoites were seen in the myofibres and thick-walled parasitic tissue cysts were found in the grey and white matter of the brain and spinal cord.