Overview

• Infection with the protozoan Cytauxzoon felis.
• Affects vascular system of lungs, liver, spleen, kidneys, and brain; bone marrow; developmental stages of RBCs.
• Uncommon in most regions, but common during the spring and summer in endemic regions.
• Affects feral and domestic cats in south-central, southeastern, and mid-Atlantic United States. Range appears to be expanding towards the eastern and northeastern United States.

Signalment

• Feral and domestic cats of all ages
• No breed or sex predilection

Signs

• Most cats have severe illness at presentation.
• Pale mucous membranes.
• Depression.
• Anorexia.
• Dehydration.
• High fever.
• Icterus.
• Splenomegaly.
• Hepatomegaly.
• Some cats may be infected but asymptomatic.

Causes & Risk Factors

• Bite of infected tick (Amblyomma americanum or Dermacentor variabilis).
• Roaming in areas shared by reservoir hosts (bobcat, Florida panther).
• Living in the same household as a cat diagnosed with cytauxzoonosis.

Differential Diagnosis

• Other causes of pancytopenia such as sepsis and panleukopenia.
• Other causes of fever and jaundice such as pancreatitis, hepatitis, and cholangitis.

CBC/Biochemistry/Urinalysis

• Bi-cytopenia or pancytopenia are the most common findings. Thrombocytopenia is almost always present.
• Moderate hyperbilirubinemia and bilirubinuria.
• Normal to mildly increased ALT.
• Mild hyperglycemia.
• Reflect changes associated with the severe anemia, caused by combination of hemolysis and hemorrhage.

Other Laboratory Tests

• Fresh blood smear-Cytauxzoon erythrocytic form; 1–3 µm in diameter; shape of a signet ring or safety pin.
• Splenic, lymph node, liver, or bone marrow aspirate-best suited to demonstrate extra-erythrocytic form.
• A PCR assay is commercially available.

Imaging

N/A

Diagnostic Procedures

N/A

Pathologic Findings

Organisms inside myeloid cells in bone marrow aspirate and in dramatically enlarged myeloid cells in vessels of multiple organs including lung, liver, spleen, kidney, and brain.

Drug(s)

• Combination of atovaquone (15 mg/kg PO q8h with a fatty meal) and azithromycin (10 mg/kg PO q24h) and supportive care is associated with survival rates of 60%.
• Imidocarb dipropionate 5 mg IM two injections 14 days apart has been recommended but is associated with survival rates of approximately 27%.
• Heparin (100–300 U/kg SC q8h or 300–900 U/kg/day as a CRI) until time of discharge (longer if develop significant coagulation problems such as pulmonary thromoboembolism).

Contraindications/Possible Interactions

N/A

Expected Course and Prognosis

• With aggressive supportive care and treatment expect 3–7 days of hospitalization with severe illness.
• Some cats develop pleural effusion (presumably secondary to pulmonary hypertension) and require thoracocentesis.
• However, cats that survive will return to normal within 2–4 weeks of discharge and appear immune to re-infection.
• Some cats remain persistently infected with the intra-erythrocytic form without overt signs.
• Without treatment, most infected cats have died within 5 days of presentation.

Zoonotic Potential

• No known risk to humans.
• Cannot be directly transmitted to another cat except by blood or tissue inoculation

Abbreviations

• PCR = polymerase chain reaction
• RBC = red blood cell

Internet Resources

http://www.vet.uga.edu/vpp/clerk/Dailey/index.htm.