Q: What do practitioners need to know about how cytauxzoonosis, or bobcat fever, is transmitted? Is it zoonotic? What population
of cats is most at risk?
Dr. Leah A. Cohn
A: Cytauxzoonosis is transmitted by the bite of a tick, especially the lone star tick (Amblyomma americanum). It cannot be transmitted directly from cat to cat, even through close contact.
Cytauxzoonosis is not a zoonotic infection. In fact, the protozoal pathogen (Cytauxzoon felis) infects cats of every kind, but only cats. Bobcats, cougars, and even tigers and lions can be infected, but the pathogen
cannot be transmitted to nonfelid animals.
The cats at greatest risk of contracting cytauxzoonosis are outdoor cats living in the South Central and Southeastern United
States during the spring, summer, and early autumn.
Q: What is the prevalence of cytauxzoonosis in the United States, and in which regions are we seeing this infection?
A: Infections were first recognized in the South Central United States—Missouri, Arkansas, and Oklahoma. Today, the disease has
a greatly expanded geographic region, extending all the way to the Mid-Atlantic states and throughout the Southeast as well
as the South Central states. The pathogen has even been identified in bobcats, the reservoir host, as far north as North Dakota.
The prevalence of infection is not known. In Oklahoma, the diagnosis accounted for almost 1.5% of feline hospital admissions
at the Veterinary Medical Teaching Hospital; most of these cats suffered from the acute illness. In some areas of the country,
the infection is completely unheard of. In others (like parts of southern Missouri) I am aware of clinics that see three cases
a week throughout the spring and early summer.
Bobcats, and domestic cats that survive initial infection, can remain healthy chronic carriers of the pathogen. In some regions,
prevalence of infection in bobcats is as high as 50%. In a study of domestic cats from a trap-neuter-release program, only
two of 494 cats in Florida and one of 75 cats in Tennessee were found to be presumably healthy carriers.1
Q: Are there typical presenting signs of cytauxzoonosis in domestic cats?
A: An owner first notices that his or her previously healthy cat goes off food and acts lethargic. The cat may cry out as if
in pain and may develop respiratory effort or distress. The veterinarian may recognize a high fever, icterus, pallor, splenomegaly
or lymphadenomegaly, and sometimes central nervous system signs including obtundation. Laboratory findings usually include
evidence of hemolytic anemia, disseminated intravascular coagulation, and hepatopathy. Often, affected cats die within five
to seven days of the appearance of the very first signs.
Cats that do survive initial infections remain chronic carriers for years. These cats are clinically healthy, but small numbers
of infected red blood cells may be observed on a peripheral blood smear.