Cytauxzoon felis is an emerging infectious disease of domestic cats. Historically, infection of domestic cats with this tick-transmitted protozoal agent has been considered uniformly fatal. For this reason, domestic cats were not believed to be a source of infection for other cats. Recently, anecdotal reports of cats that survive the acute infection have been published. These recovered cats seem to harbor the infectious red cell parasite for years and may serve as a reservoir of infection for other cats. This could help explain the seeming recent expansion in the geographic regions reporting this disease, which now covers the South Central, Southeastern, and Mid- Atlantic USA. As more cats survive infection, they could pose a risk of spreading the infection if the organism cannot be eliminated. The researchers propose to compare the ability of two anti-protozoal drug regimens to eliminate the chronic stage of infection in these cats.