Cytauxzoon felis Kier, 1979
(Figures 1-24 and 1-25)
ETYMOLOGY: Kytos (cell) + auxe (an increase) + zoon (animal) and felis (cat).
SYNONYMS:Theileria felis (Kier, Wagner and Moorehouse, 1982) Le vine, 1982.
HISTORY: This parasite was first observed in African ungulates and described as a genus distinct from Theileria based on the fact that schizogony in Cytauxzoon occurred in histiocytes while schizogony in Theileria occurs in lymphocytes. The parasite was first reported as a parasite of the domestic cat by Wagner in 1976. In 1979, Kier described in her doctoral dissertation the parasite observed in the cat as a new species, Cytauxzoon felis. In 1982, Levine considered Cytauxzoon synonymous with the genus Theileria and transferred the name "felis" to this genus. If one accepts the differentiation of Cytauxzoon and Theileria on the basis that schizogony occurs in histiocytes in the former and lymphocytes in the latter then the name would be Cytauxzoon felis. It is possible that a species of Babesia observed in a blood smear from an American bobcat (Lynx rufus) by Wenyon and Hamerton in 1930 was Cytauxzoon, but it was not recognized as such.
GEOGRAPHICAL DISTRIBUTION: Most of the cases of cytauxzoonosis have been reported from the south central and southeastern United States (Motzel and Wagner, 1990). There is a single case of cytauxzoonosis like disease reported from Zimbabwe (Foggin and Roberts, 1982), but it is difficult to ascertain the validity of this claim on the basis of the published material.
LOCATION IN HOST: Merozoites can be found in erythrocytes; typical parasitemias are 1% to 4% of the red blood cells. Due to the fulminant course of disease in the cat, it is more typical to observe the large schizonts in the walls of the venous system in histopathologic sections. Schizonts may also be observed in bone-marrow aspirates.
PARASITE IDENTIFICATION: In the erythrocytes, the merozoites are characterized by their small size. There is typically a single organism per red blood cell, but occasionally two to four organisms may be present. The ultrastructural morphology of the intraerythrocytic form was described by Simpson et al. (1985a).
Schizonts may be found in veinules of the lung, liver, spleen, bone marrow, kidney and brain (Fig. 1-24 & 1-25). The developing schizonts cause an enlargement of the infected cell which may reach 75 m in diameter. The ultrastructure of the schizont has been described (Simpson et al., 1985b). The morphology of schizonts within bone-marrow aspirates are much like those observed in histopathologic section. Again, the cells become very large and contain large numbers of developing organisms.
Cytauxzoon felis has been shown to be antigenically distinct from Babesia felis using an indirect fluorescent antibody test (Uilenberg et al., 1987).
LIFE CYCLE: The life cycle has been poorly described, and, basically, descriptions have been developed using parallels with what is known concerning the related genus Theileria. In the blood of the felid, merozoites circulate within the red blood cells (It is believed that gametogony may not occur until after the red blood cells are in the stomach of the tick.). Within the tick's stomach, it is presumed that the gametocytes undergo development and sexual fusion and ultimately produce sporozoites within the salivary glands of the tick. Once inoculated into the cat, it is not known where the sporozoites first take up residence; however, within a few days, schizonts are found within histiocytes of veins and veinules of various organs including the liver, lungs, spleen, lymph nodes, brain, and kidneys. Within 6 to 8 days after inoculation, merozoites can be found in the peripheral blood (Franks et al., 1988). It is not known how long after the appearance of organisms in the blood that infectivity for the tick vector develops.
CLINICAL PRESENTATION AND PATHOGENESIS: Usually, by the time the cat is presented, it is severely ill. Signs include anemia and depression that may be accompanied by high fever, dehydration, icterus, splenomegaly, and hepatomegaly. Packed cell volumes decrease markedly by 6 days after infection, but the anemia is regenerative (Franks et al., 1988). Plasma appears icteric on the last day or two of life. The platelet count is decrease but prothrombin or activated partial thromboplastin times are normal. Although there are no significant changes in total leucocyte counts or absolute neutrophil, monocyte, or basophil counts, lymphocyte and eosinophil counts are decreased markedly within 8 days after infection. Bone-marrow aspirates often contain large mononuclear cells containing schizonts. Almost all cats die within 9 to 15 days after infection. The percentage of red blood cells containing organisms is typically between 1% to 4%; although as many as 25% of red blood cells may be infected.
Inoculation of cats with blood from bobcats containing the merozoite stage will produce persistent parasitemias in red blood cells without inducing cytauxzoonosis (Kier et al., 1982; Blouin et al., 1984). It is believed this is due to the stage being passed being the stage that is restricted to the blood cells and that passage through the tick vector is required to produce the schizogonous stages that can typically be induced by the inoculation of splenic tissue.
TREATMENT: Attempts have been made to treat experimentally induced cytauxzoonosis with parvaquone (ClexonR) and buparvaquone (ButalexR); both drugs have been shown to be successful in treating theileriosis in cattle. In the regimen employed, the disease still proved fatal. Over a twenty-four hour period, a cat that presented with a 2-day history of lethargy and anorexia became seriously icteric and had dark brown urine (Walker and Cowell, 1995). The cat was treated with a 10 day course of enrofloxacin followed by a five-day course of tetracycline. Organisms were present in the cat after the ten-day course of enrofloxacin, but were not present in blood samples collected 6 and 15 weeks after discharge. It is not known why this cat survived; enrofloxacin is not known to be effective against protozoa. Most success in treatment has been achieved with diminizine and imidocarb. One very ill cat responded rapidly to intravenous fluids, heparin (to treat DIC) enrofloxacin and diminizine aceturate responded well. Diminizine (2mg/kg IM) was repeated weekly for 2 more treatments. Imidocarb dipropionate (5mg/kg IM, twice, 2 weeks apart) has been found to produce a 50% cure rate (Greene, 1998).
EPIZOOTIOLOGY: The life cycle appears to involve the bobcat, Lynx rufus, as the mammalian reservoir of infection (Glenn et al., 1982) and ticks, including Dermacentor variabilis, as vectors (Blouin et al., 1984). The domestic cat apparently enters the life cycle typically when it is bitten by an infected tick. After the cat is bitten by an infected tick, it will usually die of the infection in two weeks.
Cytauxzoon felis has also been found to be present in the blood of the Florida panther (Felis concolor coryi). From the infected panther, it was transmitted to a domestic cat in the buffy coat of a blood sample, and in the cat, it induced fatal disease (Butt et al., 1991). Cytauxzoon-like organisms have been observed in the erythrocytes of two cheetahs (Acinonyx jubatus) that were born and raised in Oregon, USA, and which had spent two months being trained to hunt in Namibia, Africa, as part of a release program (Zinkl et al., 1981). Inoculation of a cat with blood from one of these cheetahs produced no signs of disease or demonstrable parasitemia.
HAZARD TO OTHER ANIMALS: The fatal disease typically induced in the cat prevents it from being an important reservoir of infection. A wide range of mammalian hosts have been inoculated with Cytauxzoon felis without the induction of parasitemias (Kier et al., 1982) with sheep being the only host that appear to develop a persistent, but low, level of circulating organisms.
HAZARD TO HUMANS:Cytauxzoon felis is not known to infect humans although transmission to primates using stages from ticks have not been tried.
CONTROL/PREVENTION: The only form of control is to prevent cats that share the same geographical distribution as the bobcat from being bitten by ticks. The inoculation of a cat with stages grown in tissue culture appeared to induce an immunity (Ferris, 1979), and thus, it may be possible to someday prevent the disease in cats by vaccination.
Blouin EF, Kocan AA, Glenn BL, Kocan KM. 1984. Transmission of Cytauxzoon felis Kier, 1979 from Bobcats, Felis rufus (Schreber), to domestic cats by Dermacentor variabilis (Say). J Wildl Dis 20:241-242.
Butt MT, Bowman DD, Barr MC, Roelke ME. Iatrogenic transmission of Cytauxzoon felis from a Florida panther (Felix concolor coryi) to a domestic cat. J WIldl Dis 27:342-347.
Ferris DH. 1979. A progress report on the status of a new disease of american cats: cytauxzoonosis. Comp Immunol Microbiol Infect Dis 1:269-276.
Foggin CM, Roberts HM. 1982. A cytauxzoonosis-like disease in a cat in Zimbabwe. Zimbabwe Vet J 13:28-29.
Franks PT, Harvey JW, Shield RP, Lawman MJP. 1988. Hematological findings in experimental feline cytauxzoonosis. J Am An Hosp Assoc 24:395-401.
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Kier AB. 1979. The etiology and pathogenesis of feline cytauxzoonosis. PhD Dissertation, University of Missouri, Columbia, MO
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Simpson CH, Harvey JW, Carlisle JW. 1985a. Ultrastructure of the intraerythrocytic stage of Cytauxzoon felis. Am J Vet Res 46:1178-1180.
Simpson CH, Harvey JW, Lawman MJP, Murray J, Kocan AA, Carlisle JW. 1985b. Ultrastructure of schizonts in the liver of cats with experimentally induced cytauxzoonosis. Am J Vet Res 46:384-390.
Uilenberg G, Franssen FFJ, Perié NM. 1987. Relationships between Cytauxzoon felis and African piroplasmids. Vet Parasitol 26:21-28.
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Walker DB, Cowell RL. 1995. Survival of a domestic cat with naturally acquired cytauxzoonosis. JAVMA. 206:1363-1365.
Wenyon CM, Hamerton AE. 1930. Piroplasms of the West African civet cat (Viverra civetta) and the Bay lynx (Felis rufa) of North America. Trans Roy Soc Trop Med Hyg 24:7-8.
Zinkl JG, McDonald SE, Kier AB, Cippa SJ, Small PJ. 1981. Cytauxzoon-like organisms in erythrocytes of two cheetahs. JAVMA 179:1261-1262.
Figure 1-24.Cytauxzoonfelis schizonts in a hematoxylin and eosin stained section of the lung of a cat that died after being inoculated with the bood of a Florida panther. Schizonts can be observed lining the blood vessels in this section of lung.
Figure 1-25.Cytauxzoonfelis schizonts in a hematoxylin and eosin stained section of the lung of a cat that died after being inoculated witht the blood of a Florida panther. In this higher power image of another blood vessel in the lung shown in Fig 1-11, the schzionts can be observed to be occluding the lumen of the blood vessel.