Cats surviving natural infection with Cytauxzoon felis: 18 cases (1997-1998)

Eighteen cats surviving natural infection with Cytauxzoon felis were identi fied. All cats came from a limited geographic area in northwestern Arkansas and northeastern Oklahoma. Clinical signs in most cats were similar to tho se described for cytauxzoonosis; however, 4 cats were asymptomatic. All cas es were initially diagnosed by microscopic identification of signet ring-sh aped piroplasms in erythrocytes of peripheral blood smears. Four of 4 cats tested had detectable serum antibodies to C felis. Four different cats were positive by polymerase chain reaction (PCR). Partial sequencing of the PCR product from 1 cat revealed >99% homology with the reported sequence of C felis. Repeated examination of blood smears from 12 cats revealed that he e rythroparasitemia was generally persistent for the duration of follow-up (3 -154 days). Survival did not seem dependent on treatment, as only 1 cat was treated with a drug with potential antiprotozoal activity (imidocarb dipro pionate), and 4 cars received no treatment. The findings of this study may indicate the existence of a less virulent strain of C felis.