Confirmation of Amblyomma americanum (Acari: Ixodidae) as a vector for Cytauxzoon felis (Piroplasmorida: Theileriidae) to domestic cats

Amblyomma americanum was confirmed as a competent vector in the transmission of Cytauxzoon felis to domestic cats. Infection with C. felis was produced and replicated in four domestic felines by the bite of A. americanum adults that were acquisition fed as nymphs on a domestic cat that survived cytauxzoonosis. Numerous attempts to transmit C. felis with Dermacentor variabilis at the same time were not successful. All cats upon which infected A. americanum were transmission fed exhibited disease typical of cytauxzoonosis, and the eitiologic agent's presence was confirmed. Clinical signs including fever, inappetence, depression, and lethargy were observed beginning 13 d postinfestation. Pale mucus membranes, splenomegaly, icterus, and dyspnea were also observed during the course of the disease. Rectal temperatures of the C. felis-infected principal cats fluctuated from high to subnormal before returning to the normal range. Clinical signs of cytauxzoonsis improved by 24 d postinfestation in all but one cat, with survivors remaining parasitemic and subclinically infected with C. felis. Unengorged A. americanum and D. variabilis were collected from wild habitats to determine the minimum infection rate of C. felis in ticks from an enzootic area. Infection of C. felis was found only in wild-collected A. americanum. The minimum infection rate of C. felis in A. americanum was 0.5% (one of 178) in males, 0.8% (three of 393) in nymphs, and 1.5% (three of 197) in females. We found no wild-collected D. variabilis infected with C. felis. Our results confirm that A. americanum is a primary vector of C. felis.

Experimental infection of domestic cats (Felis domesticus) with Cytauxzoon manul from Pallas' cats (Otocolobus manul)

In a random, blind study, six domestic cats were assigned to two treatment groups that received either sterile water or dexamethasone by subcutaneous injection prior to intravenous inoculation with Pallas' cat (Otocolobus manul) blood infected with Cytauxzoon manul. A seventh domestic cat served as a control and was inoculated only with sterile water. Cats were monitored for clinical signs consistent with cytauxzoonosis, and periodically screened for hemoparasitemia. All domestic cats (6/6) that received Pallas' cat blood infected with C. manul developed a low but detectible parasitemia by 9 days post-inoculation, yet remained clinically healthy. All domestic cats (7/7) were subsequently challenged with Cytauxzoon felis and developed clinical signs typical of cytauxzoonosis within 5 days post-challenge. Affected animals were euthanized and cytauxzoonosis was confirmed by histopathology. While inoculation of domestic cats with Pallas' cat blood infected with C. manul induced a parasitemia, it did not cause disease or provide protection against challenge with C. felis. Further studies are warranted to determine the potential for interspecies transmission and disease with C. manul.

A redescription of schizogony of Cytauxzoon felis in the domestic cat

Cytauxzoon felis is a protozoan parasite that is transmitted by Dermacentor variabilis ticks and causes a uniformly fatal disease in domestic cats. In order to study schizogony and merozoite formation, D. variabilis nymphs were allowed to feed on domestic cats experimentally infected with C. felis, after which the molted adult ticks were fed on susceptible cats. Lung and liver tissues were collected from the cats during clinical cytauxzoonosis and were fixed for light and transmission electron microscopy. Some stages of parasite development were evident with light microscopy, but specific events associated with merogony could be documented only with electron microscopy. Schizogony was observed in endothelial macrophages of all tissues examined. The parasite appeared first as a multinucleated syncytium in which nuclear proliferation was evident. As the parasite syncytium developed, it became an increasingly elaborate labyrinth with extensive branches that were interconnected by thin processes of parasite cytoplasm. Organelles, including mitochondria and rhoptries, became apparent. Merozoite formation seemed to occur by rapid sequential fission along the margins of the multinucleated sporont in the cytoplasm of the host cell. As the sporont became smaller, merozoites were produced in a rosette-like configuration from the remaining parasite mass. Merozoites entered erythrocytes directly by endocytosis, without apparent injury to these cells. The sequence of events associated with merozoite formation in Cytauxzoon felis described herein differs from the previous description for this species and appears to be analogous to that described for the genus Theileria.