| Cytauxzoonosis is caused by the
Theileria
-like parasites of the genus
Cytauxzoon
of the family Theileriidae. Currently there is some dispute as to its taxonomic status, but its multiplication by schizogony in mononuclear phagocytes (macrophages) rather than lymphocytes as for
Theileria
spp
is a strong argument for its classification in a separate genus. |
| Etiology and Transmission: |
|
Cytauxzoon
spp
infect ungulates in Africa while
C
felis
is a natural parasite of wild cats (bobcat [
Lynx
rufus
] and the Florida panther [
Felis
concolor
coryi
]) of North America.
C
felis
is transmitted by the Ixodid tick
Dermacentor
variabilis
; as a parasite of wild cats its pathogenicity is unknown. Tick transmission to domestic cats results in an acute and almost always fatal disease. Most cases occur in the south and southeast states of the USA and are usually associated with access to wooded areas. However, transmission by blood infection appears to result in disease with variable pathogenicity and often is not fatal. Studies of
C
felis
in northwestern Arkansas and northeastern Oklahoma indicate that less virulent strains may be present in these areas. This is evidenced by mild to asymptomatic clinical signs and recovery without treatment for infected cats.
Cytauxzoon
spp
in African ungulates are thought to be transmitted by
Rhipicephalus
appendiculatus
. Young, stressed, or immunocompromised animals are thought to be at greatest risk. |
|  |
| Clinical Findings and Lesions: |
| Onset of clinical signs for cats infected with
C
felis
usually occurs ~10 days after infection by tick transmission. Severe signs are usually evident 6 days later. Cats are febrile, anorectic, weak, depressed, dyspneic, and dehydrated. Temperatures may be as high as 105°F (40.5°C) but usually become subnormal in extremis. Mucous membranes are often icteric. |
| At necropsy, splenomegaly, hepatomegaly, enlarged lymph nodes, and renal edema are usually observed. The lungs show extensive edema and congestion with petechial hemorrhage on serosal surfaces and throughout the interstitium. There is progressive venous distension, especially the mesenteric and renal veins and the posterior vena cava. Hydropericardium is often seen with petechial hemorrhage of the epicardium. |
| |
| Diagnosis: |
|
Hematology shows a normochromic, normocytic anemia with a declining leukopenia and pronounced lymphopenia. Occasionally, mononuclear phagocytes with schizont-filled cytoplasm are observed in peripheral blood smears. Giemsa-stained peripheral blood smears reveal pleomorphic, intraerythrocytic protozoan parasites that usually appear ~10 days after infection. Parasites may be round, oval, anaplasmoid, bipolar, or rod-shaped. Round forms are
1.0-2.2 mm in diameter, while oval forms are 0.8-1.0 µm × 1.5-2.0 µm. Once the parasitemia is >0.5%, Maltese cross and paired piriforms are seen. Infection with
Cytauxzoon
spp
must be differentiated from
Babesia
spp
, which may have similar blood forms but do not have a schizont tissue stage, and the chain-forming
Haemobartonella
felis
. |
| The tissue stage of
C
felis
is schizonts in the cytoplasm of mononuclear phagocytes that are attached to the endothelium of vessels. These phagocytes (15-250 µm in diameter) can be identified in the interstitium of the spleen, popliteal lymph node, liver, and bone marrow. |
| |
| Treatment and Control: |
| Attempts to treat this pathogen have met with little success. Parvaquone (20 or 30 mg/kg, IM, sid) and buparvaquone (5 or 10 mg/kg, IM, sid) once parasites were detected were not successful. Treatment with trimethoprim/sulfadiazine (60 mg, SC, bid) with supportive therapy has been unsuccessful (1 cat) while treatment with sodium thiacetarsamide (0.1 mg/kg, IV) for 2-3 days resulted in survival of 1 of 2 cats. More recently, 6 of 7
cats were successfully treated with diminazene aceturate (not approved in the USA) or imidocarb dipropionate (2 mg/kg, IM, 2 injections 3-7 days apart). Exclusion of cats from areas likely to be infested with the tick vector is the best method of control. |
| |
;)