Q: How do we diagnose this infection in domestic cats?
A: Microscopic examination of a peripheral blood smear will reveal signet-ring-shaped piroplasms in the red blood cells (Figure 1) of most acutely infected cats, but since illness can occur before the red blood cell stage of infection, negative smears
should be re-evaluated the next day. Alternatively, schizont-distended mononuclear cells accompany clinical illness (Figures 2A & 2B). These large cells are commonly found on aspirates of lymph nodes or spleen and are occasionally observed on blood smears.
The infection can also be confirmed by polymerase chain reaction testing.
1. Signet-ring shaped Cytauxzoon felis. (Courtesy of Dr. Marlyn Whitney, University of Missouri Veterinary Medical Diagnostic
Q: What is the latest on how we should treat cytauxzoonosis in domestic cats?
A: In a recent study, the combination of an antimalarial drug, atovaquone, and the antibiotic azithromycin was demonstrated to
result in improved survival of acutely ill cats compared with cats treated with the antiprotozoal drug imidocarb dipropionate.2 All cats also received supportive care including fluid therapy and blood transfusions when required. While only 26% of the
imidocarb-treated cats survived, 60% of those treated with the combination drug therapy lived. However, the antimalarial drug
is expensive and not readily available from nearby pharmacies.
2A & 2B. Schizont-laden macrophage (2A 100X; 2B 1000X). (Courtesy of Dr. Marlyn Whitney, University of Missouri Veterinary
Medical Diagnostic Laboratory.)
Q: How do we prevent cytauxzoonosis in domestic cats?
A: Since the infection is transmitted only by ticks, tick prevention is key. Because there are no acaricides that can prevent
tick bites perfectly, in endemic regions the most effective prevention is to apply products such as fipronyl and to keep cats
indoors to minimize exposure.
Leah A. Cohn, DVM, PhD, DACVIM
Department of Veterinary Medicine and Surgery
College of Veterinary Medicine
University of Missouri
Columbia, MO 65211
1. Haber MD, Tucker MD, Marr HS, et al. The detection of Cytauxzoon felis in apparently healthy free-roaming cats in the USA. Vet Parasitol 2007;146(3-4):316-320.
2. Cohn LA, Birkenheuer AJ, Brunker JD et al. Improved survival of cats with acute cytauxzoonosis treated with atovaquone and
azithromycin as compared to imidocarb dipropionate. J Vet Intern Med 2011;25(1):55-60.