Sign of Cytauxzoonosis in cats


 Cytauxzoon is the apicomplexan parasite in the Theileriidae family along with their closest relative, Theileria. C felis is transmitted to domestic cats by Lone Star Tick (scientific name is Amblyomma americanum). The natural host of C felis is a wild-tailed lynx (Bobcat – Lynx rufus); The host of the parasite includes the wildcat and the domestic cat that survived the infection.

Since the discovery of cytauxzoonosis in cats in Missouri in the mid-1970s, the spread of C felis has been widespread. C felis have been reported in domestic cats in Missouri, Arkansas, Florida, Georgia, Louisiana, Mississippi, Oklahoma, Texas, Kentucky, Kansas, Tennessee, North Carolina, South Carolina, Nebraska, Iowa, and Virginia. Anecdotal reports of C felis infection in domestic cats in other states including Alabama, southern Illinois and Ohio.

Unusual and natural hosts:

Domestic cats have been considered an unusual or lethal host of C felis due to an acute and lethal course of illness; however, there are reports of domestic cats that have survived a natural infection that requires and does not require treatment. As a natural host, the lynx often develops subclinical infection followed by a chronic parasite. Rare cases of fatal cytauxzoonosis in dumbbells have been reported. Cytauxzoonosis has been reported in a number of other cases of the feral family of cats in the United States and other countries, with both fatal and non-fatal results. Infections have been reported in Cuga, Black Panther and Tiger in the United States, and two suspected but unconfirmed cases in gazette. Cases of C felis infection of wild feline species have been reported in other countries including lion, jaguar, puma, the ocelot and the small spotted cat. In the early 1980s, inter-species C felis transmission was investigated to further identify potential natural and anomalous hosts among 91 wildlife, laboratory animals and farm animals. indoor farm. The low-tailed lynx and domestic cats are the only animals confirmed to be susceptible to C felis.

Transmission factors and risks:

C felis is transmitted by the Lonely Star tick, A americanum. Cytauxzoonosis is usually diagnosed between April and September, correlating with seasonal flea activity depending on the climate. Cats live near wooded areas, with low population density, especially close to natural or unmanaged habitats, where both ticks and close-tailed lynx are at risk. most infected. Experimental infection was induced by parenteral administration of tissue homogenates (SC: subcutaneous injection, IP: peritoneal drug symbol and IV: intravenous injection) from acutely infected cats. However, No infection was caused when these tissues were used in the stomach or when uninfected cats were kept with infected cats in the absence of arthropod vectors, suggesting that the Oral transmission and “cat to cat” does not occur. A recent study failed to document the cyclic transmission of C felis from 2 chronically infected mothers to 14 healthy kittens, suggesting that vertical transmission may not be as common, if.

Life cycle and Pathogenesis:

After passing from a tick to a cat, C felis undergoes two main stages: detachment reproduction and oocyte development. First, the infection infects WBCs (mononuclear phagocytosis) and undergoes splitting reproduction (asexual reproduction) to form schizophrenia. Schizophrenic WBCs were detected ~ 12 days after experimental infection and increased in diameter from 15 µm to 250 m. They are most commonly found in the lymph nodes, spleen, liver, lungs and bone marrow but have been noted in many organs and are sometimes seen on peripheral blood smear tests.

WBCs with schizophrenia are a major cause of morbidity and mortality; They are found mainly in the lining and often clog blood vessels. These “parasitic thrombosis” lead to ischemia and tissue necrosis. Then, WBCs infected with the schizophrenia rupture and release piroplasms (merozoite), which infect the red blood cells. The piroplasms in the red blood cells are quite harmless, with an average parasitic count of 1% –4%; however, a higher number of parasites (ie> 10%) was noted. During acute infection, detection of merozoite-infected erythrocytes is variable and is correlated with an increase in body temperature and a decrease in the number of leukocytes. If not treated, Survivors often still suffer from chronic parasites and at least one cat has been shown to be fully immune to subsequent infections. The chronic parasite has been formed through the injection of merozoite-infected red blood cells. These chronic parasitic-infected cats did not develop an overt clinical illness but were not immune to the subsequent challenge of a sputum / schizophrenic infection, indicating that a period of fragmented reproductive tissue is necessary to establish immunity in domestic cats.

Three Piroplasms C felis in erythrocytes in cat peripheral blood smear assay (50X) |  Cytauxzoonosis in cats
Three Piroplasms C felis in erythrocytes in cat peripheral blood smear assay (50X) | Cytauxzoonosis in cats

Clinical findings and injuries:

The onset of clinical signs in cats infected with C felis usually occurs 5–14 days (average ~ 10 days) after a tick-borne infection. Non-specific signs such as depression, lethargy, and loss of appetite are the most common problems. Fever and dehydration are the most common physical findings; body temperature gradually increases, possibly up to 106 ° F (41 ° C). Other findings include jaundice, lymph node enlargement, and hepatosplenomegaly. In bad condition, cats often experience hypothermia, have difficulty breathing, and vocalize as if in pain. Without treatment, death usually occurs within 2-3 days after the body reaches its maximum temperature. On autopsy often found enlarged spleen, enlarged liver, enlarged lymph nodes and kidney edema. The lungs exhibit extensive edema and congestion, accompanied by spotting haemorrhage on the serosa’s surface and throughout the interstitial spaces. There is progressive varicose veins, especially the mesenteric and renal mesenteric veins and posterior vena cava. Pericardial effusion is often seen with spotting hemorrhages of the pericardial visceral leaf.

When first described, the reported mortality from C felis infection was close to 100%. A study of C felis in northwest Arkansas and northeastern Oklahoma indicated survival after natural infection in 18 cats with and without treatment; These cats at first appear “less ill”, have no temperatures> 106 ° F (41 ° C), and never experience hypothermia. Similar sporadic reports in other regions also appeared. Some of the theories about survivability in these cats include:

  • The path of infection is not typical
  • Innate immunity in certain cats
  • Increases the ability to detect the host that carries pathogens
  • Reduced toxicity when a strain is reduced or a new strain emerges
  • Dosage of infectious vaccines
  • Duration and type of treatment.


The most common abnormalities on CBC in animals with cytauxzoonosis include leukopenia with toxic neutrophils and thrombocytopenia with normal erythrocytes, ischemic anemia seen at a later stage. The most common biochemical abnormalities are hyperbilirubinemia and hypoalbuminemia but can vary depending on the organ systems affected by parasitic thrombosis and ischemia accompanied by tissue necrosis. Other, less consistently detected, abnormalities include elevated levels of liver enzymes and hyperemia.

A rapid diagnosis requires microscopic observations of piroplasms or schizonts. Observation of piroplasms on the peripheral blood smear test is variable; they are seen with an increase in body temperature and usually manifest 1–3 days before death. There are anecdotal reports of higher sensitivity when blood is drawn from smaller vessels (eg, ear vein injections) in preparation for a peripheral smear test. On a well prepared peripheral blood smear test (most commonly Wright-Giemsa, Giemsa, Romanowsky), when detectable, merozoite can be seen on average 1% –4%, with billions Extremely high percentages (ie> 10%) were reported in some cases. They come in a variety of shapes and can be round, oval, anaplasmoid, binucleated, or rod-shaped; However, The most common circular and oval-shaped piroplasm forms. The circular form measures 1–2.2 µm, while the oval shape measures 0.8-1 µm × 1.5–2 µm. They are pale in the center and contain a small, dark red nucleus, rounded to a crescent shape on one side. When the ratio of parasites in the blood is ~ 0.5%, pairs of piriforms and Maltese cross are visible. Peripheral testing must be carefully examined to exclude Mycoplasma haemofelis, Howell-Jolly body, stain precipitate(roughly translated: precipitated stains) and water artifact.

The schizophrenic phase precedes the formation of the erythrocyte phase. Occasionally, the schizophrenia can be seen in the peripheral blood smear assay, especially at the bristles, and may be mistaken for large, low-powered clumping platelets. In the absence of detection of red or schizophrenic piroplasms on the peripheral blood smear test, a quick diagnosis should be made by performing a fine needle aspiration test (FNA- Fine Needle Aspiration) of the lymph node. peripheral, spleen or liver to identify schizophrenic cytology. These phagocytes are 15–250 µm in diameter and contain an egg-shaped nucleus with a distinctive, prominent, large, dark nucleus. The cytoplasm is often greatly swollen, with many small deep basophilic fractions representing developing merozoite.

In the absence of these observations, a diagnostic PCR test can be performed with greater sensitivity and specificity than microscopy. This test is recommended in suspected cases where parasites are not observed, as well as to confirm the identification of piroplasms or schizophrenia.

C felis schizonts A) on the fur margin of the cat peripheral blood smear test (100X) and B) in a peripheral lymph node exposure of a cat with acute cytauxzoonosis (50X) |  Cytauxzoonosis in cats
C felis schizonts A) on the fur margin of the cat peripheral blood smear test (100X) and B) in a peripheral lymph node exposure of a cat with acute cytauxzoonosis (50X) | Cytauxzoonosis in cats

Treatment and Control:

Historically, attempts to treat cytauxzoonosis with a variety of antiparasitic drugs (parvaquone, buparvaquone, trimethoprim / sulfadiazine, sodium thiacetarsamide) have been unsuccessful. In one study, five out of six cats and another cat were successfully treated with diminazene aceturate (not approved in the US) and imidocarb dipropionate (2 mg / kg, IM: intramuscularly, twice injections 3 to 7 days apart), respectively.

The successful treatment was most appropriate in a large series of cases resulting in a survival rate of 64% of cats who were given a combination of atovaquone (15 mg / kg, orally, 3 times a day for 10 days) and azithromycin (10 mg / kg / day, orally, for 10 days) and supportive care. Atovaquone is an ubiquinone analogue bound to cytochrome b. In a study of C felis-infected cats treated with atovaquone and azithromycin, a second type of C felis cytochrome b (cytb1) was associated with increased survival in cats with phenotype this second compared to other second types. The future development of a rapid means of identifying cytb1 C felis in infected cats may help to better predict survival when treated.

Supportive care, including intravenous infusion therapy and heparin (100–200 U / kg, subcutaneously, 3 times a day) should be given in all cases. Nutritional support should be provided through the esophageal tube or through the nasal feeding tube, which also facilitates the use of oral medications (eg, atovaquone and azithromycin). Oxygen therapy and blood transfusion should be performed as needed. Anti-inflammatory drugs can be ordered in the case of a fever that does not stop; however, NSAID use is contraindicated in uremic or dehydrated cats. Once the diagnosis is reached and treatment is initiated, it is recommended to minimize stress and handle with hands. Recovery, including fever reduction, is usually slow and can take 5–7 days. The surviving cats will make a full clinical recovery, including resolution of hematological and biochemical abnormalities within 2-3 weeks. Some of the cats that survive are continually infected with piroplasms and possibly a nest of infection. In one study, high-dose diaminazene diaceturate (4 mg / kg / day, IM: intramuscularly, for 5 consecutive days) did not reduce the severity of the parasite in cats with chronic C felis infection and resulted in adverse drug reactions.


Regular tick prevention should be applied to prevent cytauxzoonosis; however, it can still occur in cats even though it is treated. In one study, a cat tick necklace containing 10% imidacloprid 10% / flumethrin 4.5% prevented A americanum tick from attaching, sucking blood and transmitting C felis in 10 cats infected with the tick after wearing. ring. In the same study, the tick attached and sucked on 10 out of 10 tested cats that were not treated with a tick-proof collar, and 9 out of 10 tested cats were infected with C felis. Keeping cats away from potential tick vector (i.e. indoors only) areas is still considered the best precautionary measure.