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Abstract
Although cytauxzoonosis has historically been nearly 100% fatal in domestic cats, increasing numbers of reports of infected cats demonstrating less severe disease suggest the development of different strains of Cytauxzoon felis. To test this hypothesis, the genetic variability of C. felis in both current and historical samples was assessed, determining if unique genetic sequences varied geographically, in different felid hosts, and in pathogenicity to domestic cats. In addition, the existence of asymptomatic C. felis infection in domestic cats was examined. The genetic variability of C. felis was evaluated from both surviving and fatally infected domestic cats from Arkansas and Georgia, using the first and second ribosomal internal transcribed spacer (ITS) regions as markers to assess genotypic variability. The identification of unique C. felis genotypes obtained from different geographic areas and the association of particular ITS genotypes with outcome of infection support the existence of distinct parasite strains. ITS sequencing of C. felis obtained from historical histologic specimens from infected cats diagnosed with cytauxzoonosis at necropsy identified genetically distinct C. felis populations and, together with data from contemporary samples, supports a diverse population structure for C. felis. Finally, real-time PCR was utilized to identify C. felis infection among a population of domestic cats that were clinically healthy but at higher risk for parasite exposure. Genetically distinct parasite populations that were identical to those detected from clinically ill infected cats were identified within the asymptomatically infected domestic cats and were also present in samples from bobcats, the known reservoir host. In total, this investigation demonstrates that C. felis sequence diversity exists among infected North American felids. However, sequence variations within the ITS regions do not appear to be useful as markers of C. felis pathogenicity in domestic felid hosts. The detection of asymptomatic C. felis infection in clinical healthy domestic cats warrants further investigation to determine if these naturally infected domestic cats can serve as an additional reservoir host for C. felis, altering the currently accepted paradigm of C. felis transmission to domestic cats solely through bobcats as the reservoir host.