Felis ISSN 2398-2950


Contributor(s): Leah Cohn, Maggie Fisher, Hany Elsheikha


  • Cause: often fatal tick-borne protozoal infections of cats in the US, caused by Cytauxzoon felis Cytauxzoon felis. Cytauxzoon spp identified in Europe differs from C. felis and is probably less virulent.
  • Tick transmitted hemoparasite.
  • Mainly affects cats with outdoor access in areas where tick vectors are prevalent.
  • Signs: non-specific in the acute phase, with sudden onset of fever, depression, anorexia, anemia, jaundice and dyspnea.
  • Treatment: attempted treatments have not been very effective and infected cats usually die.



  • Disease in the USA is caused by the infection of cats with Cytauxzoon felis.
  • Disease in Europe is caused by Cytauxzoon spp which seems less virulent and causes a mild form of the disease.


  • A tick-transmitted protozoal infection in which the endothelial-associated mononuclear cells, and then the red blood cells are parasitized.
  • Incubation following the bite of an infected tick takes just over two weeks, then cats rapidly become acutely ill.
  • Following infection, tissue macrophages become laden with the schizont stage of the protozoal infection.  It is this tissue stage of infection that is associated with clinical illness.
  • Schizonts form by binary fission - these enlarge until they block blood vessels and result in tissue damage, thrombosis, circulatory impairment, and a severe systemic inflammatory response, which can lead to multi-organ failure and death.
  • Merizoites erupt from the mononuclear cell and are endocytosed by red blood cells, resulting in erythrocytic infection with piroplasms. These piroplasms may appear as small anaplasmoid forms, bipolar forms or Maltese crosses.
  • Erythrocytic forms seen in blood from as early as 10 days post-infection, but death may occur prior to overt erythrocytic infection.  The number of infected RBC typically increases until the cat succumbs.
  • Red blood cells parasitized in large numbers - removed from the circulation - results in anemia and sometimes jaundice.
  • Death normally follows within days of clinical signs appearing.
  • Pyrexia, often severe, is a near uniform finding in the early stages of illness.
  • Hypothermia Hypothermia is often identified in the final stages of infection, shortly prior to death.


  • Incubation period of about two weeks from bite of the infected tick.
  • Rapid course of the disease resulting in death within a week of clinical signs appearing.


  • Believed to be transmitted by the ticks Dermacentor variabilis and Ambylomma americanum in the USA. The tick vector in Europe is not identified yet.
  • The bobcat (Lynx rufus) is the natural reservoir host, but chronically infected domestic cats play a role in this geographic expansion.
  • Not transmitted from cat to cat, even with close contact.
  • Usually associated with an outdoor lifestyle.
  • Cytauxzoon spp infections have been reported in domestic and wild felids in Spain, Portugal, France, Italy, Romania and Turkey.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Legroux J P, Halos L, René-Martellet M (2017) First clinical case report of Cytauxzoon sp. infection in a domestic cat in France. BMC Vet Res 13 (1), 81 PubMed.
  • Wang J L, Li T T, Liu G H et al (2017) Two tales of Cytauxzoon felis infections in domestic cats. Clin Microbiol Rev 30 (4), 861-885 PubMed.
  • Alho A M, Silva J, Fonseca M J et al (2016) First report of Cytauxzoon sp. infection in a domestic cat from Portugal. Parasit Vectors (1), 220 PubMed.
  • Conner B J, Hanel R M, Brooks M B et al (2015) Coagulation abnormalities in 5 cats with naturally occurring cytauxzoonosis. J Vet Emerg Crit Care (San Antonio) 25 (4), 538-545 PubMed.
  • Frontera-Acevedo K & Sakamoto K (2015) Local pulmonary immune responses in domestic cats naturally infected with Cytauxzoon felis. Vet Immunol Immunopathol 163 (1-2), 1-7 PubMed.
  • Lloret A, Addie D D, Boucraut-Baralon C et al (2015) Cytauxzoonosis in cats: ABCD guidelines on prevention and management. J Feline Med Surg 17 (7), 637-641 PubMed.
  • Sherrill M K, Cohn L A (2015) Cytauxzoonosis: Diagnosis and treatment of an emerging disease. J Feline Med Surg 17 (11), 940-948 PubMed.
  • Cohn L A, Birkenheuer A J, Brunker J D et al (2011) Efficacy of atovaquone and azithromycin or imidocarb dipropionate in cats with acute cytauxzoonosis. JVIM 25 (1), 55-60 PubMed.
  • Allison R W, Fielder S E, Meinkoth J H (2010) What is your diagnosis? Blood film from an icteric cat. Vet Clinic Pathol 39 (1), 125-126 PubMed.
  • Birkenheuer A J, Le J A, Valenzisi A M et al (2006) Cytauxzoon felis infection in cats in the mid-Atlantic states: 34 cases (1998-2004). JAVMA 228 (4), 568-571 PubMed.
  • Meier H T & Moore L E (2000) Feline cytauxzoonosis - a case report and literature review. JAAHA 36 (6), 493-496 PubMed
  • Kier A B, Wagner J E, Kinden D A et al (1987) The pathology of experimental cytauxzoonosis. J Comp Pathol 97 (4), 415-432 PubMed.
  • MacWilliams P S (1987) Erythrocytic rickettsia and protozoa of the dog and cat. Vet Clin NA Small Anim Pract 17 (6), 1443-1461 PubMed.

Other sources of information

  • Day M J (2016) Arthropod-borne Infectious Diseases of the Dog and Cat. 2nd edn. CRC Press.
  • Elsheikha H M & Naveed Khan (2011) Essentials of Veterinary Parasitology. 1st edn. Caister Academic Press, UK.