Second illness due to subsequent Cytauxzoon felis infection in a domestic cat

A castrated male domestic shorthair cat from a wooded area in Missouri had recovered from typical severe cytauxzoonosis at 4 years of age, after intensive in-hospital supportive care and administration of atovaquone and azithromycin. At 11 years of age, the same cat again experienced an acute febrile illness compatible with cytauxzoonosis. Intraerythrocytic piroplasms typical of Cytauxzoon felis were identified by cytology. The owners opted for euthanasia but allowed collection of splenic and hepatic tissue for histopathologic examination. Schizont-laden macrophages were identified in both tissue specimens, confirming active cytauxzoonosis at the time of the cat's death.

Although cats that have recovered from cytauxzoonosis can harbor red blood cell piroplasms for many years without apparent clinical illness, repeat illness owing to either disease recrudescence or repeat infection has never been documented. In fact, recovered cats have been thought to be resistant to reinfection and subsequent illness. This report describes a cat that had recovered from documented cytauxzoonosis 7 years previously and then developed a subsequent clinical illness typical of cytauxzoonosis, which was accompanied not only by intraerythrocytic piroplasms, but also by schizont-laden tissue macrophages pathognomonic of clinical cytauxzoonosis.