A 3-year-old domestic short-haired cat from central Texas died shortly after arrival at a veterinary clinic. On gross necropsy, lesions were minimal; however, histologically every tissue examined demonstrated vascular occlusion with numerous intracytoplasmic schizonts within macrophages. The schizonts were approximately 40 microns in diameter and contained numerous 1-3 micron merozoites.
This cat died from infection with Cytauxzoon felis. C. felis is a protozoal hemoparasite that leads to rapidly progressive, systemic fatal disease in domestic felids. The protozoan is transmitted by Ixodid ticks or through ingestion of infected blood or tissue. The organisms undergo maturation phases within the erythrocytes and macrophages before becoming infective and ready for uptake by the tick again. Histologically, it is very common to find vessels in multiple organs completely occluded by large numbers of merozoites (as noted in the image).
The North American bobcat is the natural reservoir host and is often asymptomatically infected. However, when a domestic cat is infected, the results are typically fatal. C. felis is considered endemic in areas where the bobcat and tick vector coincide, but has primarily been reported in the southeastern and southern midwestern states. Treatment is difficult, because clinical signs progress to death very quickly and there are few effective treatments available.
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