Cytauxzoonosis is a protozoan infection of cats that is spread via tick bites. It is a serious condition — most infected cats die as a result.
Cytauxzoonosis affects only cats and poses no known risk to people. An infected cat cannot directly transfer the infection to another cat — the tick vector is essential for transmission.
This disease was first diagnosed in 1976 in Missouri. Since then it has been identified in 12 states, mainly in the southeastern and south-central regions of the United States. It is thought bobcats may provide a reservoir of infection, possibly with mountain lion involvement in some regions.
The tick Dermacentor variabilis, a flat, reddish-brown tick, is responsible for transferring infection between animals.
Cytauxzoonosis has an incubation period of about 2 weeks from the tick bite to the first signs of illness. After symptoms show up, the deterioration tends to be rapid, with most cats dying 1 week later.
In the early stages, the symptoms are quite general, but serious nonetheless. These include:
- High fever
- Severe lack of energy
- Appetite loss
- Breathing difficulties
- Serious weakness
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The cause of this distressing condition is a protozoan (single-celled) parasite called Cytauxzoon felis.
Cytauxzoon is injected into the cat’s bloodstream by the bite of an infected tick. The parasite reproduces inside tissue cells and reaches such numbers that they block blood vessels, resulting in tissue damage.
As the infection progresses and the Cytauxzoon completes its life cycle, the parasite moves into blood cells. This is the terminal stage where cats usually succumb to the illness.
Diagnosis can be tricky. By the time the clinical signs show, the tick that bit and introduced the infection is long gone. Given the vague nature of the symptoms, the veterinarian’s suspicions may be aroused if an ill cat lives in a region where Dermacentor is endemic.
Again, diagnosis is made even more difficult in that invasion of the red blood cells happens only at the very end, just before death. This is frustrating because it is possible to see the parasites inside the blood cells on microscopy — but many cats must be euthanized before a definitive diagnosis is made.
Changes on routine blood tests are suggestive of liver damage and anemia, and can point toward the problem but do not definitively diagnose it.
This student slideshow provides an overview of this condition (and you’ll learn how to pronounce it):
Despite valiant attempts to find an effective treatment, these efforts are largely unsuccessful. Vets have tried various antibiotic, antimalarial and antiprotozoal drugs, but no reliable treatment has been found.
There are anecdotal reports of occasional responses from cats given the drug imidocarb. Apart from this, the only other options are supportive care with intravenous fluids to prevent shock and antibiotics to reduce the likelihood of secondary bacterial infections to which the patient is vulnerable because of being so ill.
The most constructive means of prevention is to keep cats away from woods in regions where Dermacentor is endemic.
Also, it is imperative to keep the cat protected with products that kill ticks to decrease the likelihood of being bitten. However, even when exposed to effective products, ticks do not necessarily die straight away, and there is still a risk the cat will be bitten — and infection will be transferred — before the tick dies.
- “Feline cytauxzoonosis — a case report and literature review.” Meier & Moore. JAAHA, 36: 493–496.
- “The pathology of experimental cytauxzoonosis.” Bet et al. J Comp. Pathol, 97: 415–432.
This pet health content was written by a veterinarian, Dr. Pippa Elliott, BVMS, MRCVS. It was last reviewed March 1, 2017.