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Cytauxzoon felis

  • Cytauxzoon is classified in the order Piroplasmida and family Theileriidae
    • This family has both an erythrocytic and a tissue (leukocytic) phase
  • The Babesiidae, a related family, is characterized by having a primarily erythrocytic phase in the mammalian host
    • Its morphological features are indistinguishable from the erythrocytic form of Cytauxzoon
  • Cytauxzoon felis, B. equi, and B. rodhaini have been linked to both the babesias and theilerias by RNA gene sequence analysis
    • It has been suggested that these organisms be reclassified within a separate family

Life Cycle

  • Large schizonts of C. felis develop in macrophages
    • In Theileria the exoerythrocytic stage occurs primarily within lymphocytes
  • In C. felis, schizonts develop within mononuclear phagocytes, initially as indistinct vesicular structures and later as large, distinct nucleated schizonts that actively undergo division by true schizogony and binary fission
  • Later in the course of the disease, schizonts develop buds (merozoites) that separate and eventually fill the entire host cell
  • Each schizont may contain numerous merozoites
    • Ultrastructurally, schizonts lack a parasitophorous vacuole, and individual merozoites possess rhoptries
  • The host cell ruptures, releasing merozoites into the tissue fluid and blood
  • Merozoites are then believed to enter erythrocytes to form the intraerythrocytic stage


  • Ticks are implicated as the natural vector for Cytauxzoon
    • Most cases of infection have been associated with the presence of these parasites on the hosts
    • Experimentally, Dermacentor variabilis can transmit the organism from bobcats to domestic cats. In a white tiger that developed a natural, fatal infection in Florida, two female Lone Star ticks (Amblyomma americanum) were present on the inguinal skin.
  • Clinically, the disease in cats is characterized by fever, depression, dyspnoea, anorexia, lymphadenopathy, anaemia and icterus leading to death in three to six days
  • Gross findings include pale or icteric mucous membranes, petechiae and ecchymoses in the lung, heart, lymph nodes and on mucous membranes, splenomegaly, lymphadenomegaly, and hydropericardium
  • Microscopically, numerous large schizonts are present within the cytoplasm of endothelial-associated macrophages
    • Infected macrophages become markedly enlarged (up to 75μm) and may occlude the lumen of numerous vessels of many tissues, in particular the lungs
    • Minimal inflammatory reaction is present in tissues


  • Merozoites within erythrocytes, best seen on peripheral blood or tissue impressions, are variable in morphology and can occur as round, oval, or signet ring-shaped bodies
    • Are 1-5 micrometers in diameter
    • Small, peripherally placed basophilic nucleus
  • Organisms that must be distinguished from the intraerythrocytic phase of C. felis include Babesia and Hemobartonella
    • The blood stage may appear similar to the ring forms of Hemobartonella and to the piriforms of Babesia
    • Unlike Cytauxzoon, babesiosis and hemobartonellosis do not have a tissue stage of infection
  • Differential diagnosis for the tissue phase of cytauxzoonosis includes other small (less than 5 μm), intrahistiocytic organisms such as Toxoplasma, Leishmania and Histoplasma

Cytauxzoon Learning Resources
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Piroplasmida Flashcards
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Full Text Articles
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Cytauxzoonosis. Birkenheuer, A.; The North American Veterinary Conference, Gainesville, USA, Small animal and exotics. Proceedings of the North American Veterinary Conference, Orlando, Florida, USA, 17-21 January, 2009, 2009, pp 634-635