Toxoplasma-like sporozoa in an aborted equine fetus.

Multifocal areas of necrosis and infiltrations of mononuclear cells were seen in lung specimens of an equine fetus aborted 2 months before term. Extracellular and intracellular protozoa were seen in the alveolar tissue. Individual organisms were 4 microns by 2.5 microns, and cyst-like structures were 25 microns by 18 microns. Organisms did not stain with periodic acid-Schiff or by use of the immunoperoxidase and peroxidase-antiperoxidase method for Toxoplasma gondii. Twelve days after abortion, the mare had serum antibody titer of less than 1:10 against T gondii.