Cytauxzoonosis

Lore & Background

Cytauxzoon felis is a protozoan that infects blood cells of cats and is transmitted by tick bites, primarily the Lone star tick. The natural reservoir is the bobcat, which carries the organism without severe illness. Domestic cats were historically considered dead-end hosts because infection was thought to invariably lead to death. The disease was originally believed limited to the south central and southeastern United States, but cases have appeared in the mid-Atlantic region and as far north as Pennsylvania and North Dakota in bobcats.

The life cycle includes a tissue phase (schizogony in mononuclear phagocytic cells) and an erythrocytic phase. The tissue phase, where infected macrophages clog venules in organs, is associated with clinical disease. Diagnosis is made by finding piroplasms on blood smear, by needle aspirates of affected organs, or by PCR testing. Key rule-outs include Mycoplasma haemofelis and tularemia.

Treatment has evolved: imidocarb dipropionate with supportive care yields only 25% survival, while a combination of atovaquone and azithromycin with supportive care achieves 60% survival. Cats that survive become persistent carriers and should be kept indoors to prevent further tick-borne transmission.

Reader's Guide

Cytauxzoonosis represents a significant emerging infectious disease in domestic cats, with its geographic range expanding beyond its original description in the south central United States. The disease highlights the interplay between wildlife reservoirs (bobcats) and domestic animals, and the role of tick vectors in disease emergence. Historically considered a death sentence, the shift in understanding—that some cats survive and that treatment can be effective—has changed veterinary practice. The 60% survival rate with atovaquone and azithromycin combination therapy marks a major advance. The disease also illustrates the importance of accurate diagnosis, as its signs mimic other conditions like Mycoplasma haemofelis and tularemia. Ongoing uncertainties remain, including why some cats develop severe disease while others remain asymptomatic, and whether different strains of C. felis vary in virulence. Prevention focuses on keeping cats indoors and using tick treatments, though these do not fully prevent bites. Surviving cats pose a risk as carriers, potentially infecting other cats via ticks. Cytauxzoonosis thus serves as a model for understanding vector-borne diseases that cross wildlife-domestic animal boundaries.

Did You Know?

• Cytauxzoon felis is a protozoan, not a bacterium, virus, or fungus.
• The disease poses no zoonotic or agricultural risk because it infects only the family Felidae.
• A combination of atovaquone and azithromycin with supportive care yields a 60% survival rate in sick cats.
• Bobcats are the natural reservoir host and remain persistent carriers after mild or subclinical infection.