Have You Heard? A new treatment option for feline cytauxzoonosis (script)

One of the scariest tick-borne pathogens is Cytauxzoon felis. While cats with cytauxzoonosis have been known to survive the illness with or without specific drug therapy, this disease is generally considered fatal. No antiprotozoal protocol has been successful in altering the course of this disease, but supportive care and treatment with imidocarb dipropionate has become the accepted therapy.

Recently, a study was conducted to compare the efficacy of two treatment options—a combination of atovaquone and azithromycin or imidocarb dipropionate alone. In a preliminary study, use of this combination of an antimalarial and antibacterial drug was encouraging.

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Eighty cats with acute cytauxzoonosis from a variety of veterinary clinics in five endemic states participated in this study. Most of the cats were young adults with outdoor access and presented with vague clinical signs of lethargy and anorexia.

After diagnosis, each cat was randomly assigned to one of two treatment groups. One group was treated for 10 days with atovaquone (15 mg/kg orally three times daily) and azithromycin (10 mg/kg orally once daily). Cats in the imidocarb group were pretreated with subcutaneous atropine and 15 minutes later received an intramuscular injection of imidocarb dipropionate at a dose of 3.5 mg/kg. The injection procedure was repeated seven days later. Treating veterinarians were at liberty to provide supportive care and other concomitant treatments. The cats were discharged when they were afebrile and eating voluntarily.

All therapies were recorded, and medical records were provided to the study authors. Anticoagulated blood samples were used for PCR identification of C. felis. Parasitemia was quantified, and the specific pathogens were genotyped. The primary endpoint for each participant was either survival to discharge, or death.

The findings revealed that 60% of the cats treated with the atovaquone-azithromycin combination survived, as compared with only 26% of those in the imidocarb treatment group. Another interesting finding was that regardless of treatment, cats with lower parasitemia were more likely to survive, as were cats with higher white blood cell counts and lower total bilirubin concentrations. However, the authors of this study caution that because of the small study size, these parameters cannot be used as predictors of outcome. The results also showed that the cats were infected with a variety of pathogen genotypes, and several individuals were infected with multiple isolates.

The results of this study indicate that treatment with atovaquone and azithromycin improves survival to discharge for cats with acute cytauxzoonosis, although mortality remains high. As noted by the authors, the high rate of mortality associated with this infection should prompt veterinarians to focus their efforts on prevention by minimizing cats' exposure to ticks.

Cohn LA, Birkenheuer AH, Brunker JD, et al. Efficacy of atovaquone and azithromycin or imidocarb dipropionate in cats with acute cytauxzoonosis. J Vet Intern Med 2011;25:55-60.