Neuropathology of Natural Cytauxzoon felis Infection in Domestic Cats.

Cytauxzoonosis is a tick-borne disease of felids caused by the protozoan Cytauxzoon felis. This article characterizes the neuropathologic changes in 8 cases of natural C. felis infection in domestic cats with typical clinical signs and pathologic changes in multiple organs. Histologic changes in the brain included intravascular schizont-laden macrophages in leptomeningeal and parenchymal arterioles and venules. Small capillaries throughout the gray and white matter and choroid plexus also appeared occluded. Affected vessels were often surrounded by small to moderate numbers of lymphocytes and plasma cells and multiple areas of hemorrhage. Vasculitis and fibrin thrombi were occasionally present. Parenchymal changes consisted of variable degrees of vacuolation of the gray and white matter, with microgliosis, astrocytosis, astrogliosis, and multiple microhemorrhages. Multiple well-demarcated areas of necrosis observed in 4 cases were characterized by marked vacuolation of the gray or white matter, with necrotic neurons containing shrunken hypereosinophilic cytoplasm and pyknotic nuclei, nuclear debris, swollen axons, and scattered foamy macrophages. The changes in the brains of affected cats were attributed to vascular occlusion and secondary ischemia caused by the protozoal infection.