Cytauxzoonosis in Cats

What Is Cytauxzoonosis in Cats?

Cytauxzoonosis is a tick-borne (transmitted by tick bites) parasitic disease caused by Cytauxzoon felis, a protozoal (single-celled) organism that infects the blood cells of cats.

The parasite infects white blood cells in the immune system, causing cells to swell. The swollen cell then blocks or clogs blood vessels throughout the body, resulting in inflammation and damage to tissues and organs. A parasite can also infect red blood cells, resulting in anemia that further damages tissues and organs due to a lack of oxygen.

Geographically, cytauxzoonosis has been reported in South America, Europe, Asia, and the United States. Within the United States, Cytauxzoon felis has been identified primarily in the Central, South-central, Southeastern, and mid-Atlantic regions. Cytauxzoonosis is most diagnosed from April to September, correlating with tick season.

Cytauxzoonosis was first reported in the United States in 1976 and is considered an emergency disease. While it is still uncommon in domestic cats, it is reported to affect up to 79% of wild cats in endemic regions.

Symptoms of Cytauxzoonosis in Cats

Clinical signs of cytauxzoonosis in cats start off minor but can quickly progress to a life-threatening illness. Clinical signs typically become apparent 5 to 14 days after infection.

Some common symptoms include:

• Fever (90 percent of cats with cytauxzoonosis will have a fever up to 106°F)

• Anorexia

• Vomiting 

• Depression

• Lethargy  

• Dehydration

• Weakness 

• Paleness

• Jaundice (yellowing of the skin, mucous membranes, and whites of the eyes)

• Abdominal pain (enlargement of liver or spleen)

• Enlarged lymph nodes

• Increased heart rate and/or respiratory rate

• Seizures

• Coma

Causes of Cytauxzoonosis in Cats

Cytauxzoon felis is spread through tick bites—most commonly the lone star tick (Amblyomma americanum) or the American dog tick (Dermacentor variabilis). It is commonly referred to as “bobcat fever” because the natural host is the bobcat (Lynx rufus). Most bobcats will not show any signs of illness but serve as asymptomatic carriers that infect the local tick population.

The ticks go on to infect other members of the cat family, wild or domestic. Unfortunately, cytauxzoonosis can be deadly to most other types of cats. Cats cannot transmit cytauxzoonosis to each other but must be bitten by a tick for transmission to occur. Additionally, cats cannot acquire cytauxzoonosis from ingesting a tick; the tick must bite the cat.

Cytauxzoonosis is limited to the cat family and cannot infect humans or dogs.

How Veterinarians Diagnose Cytauxzoonosis in Cats

Your veterinarian will conduct a thorough physical examination to assess for fever, jaundice, and abdominal pain. Providing your vet with a detailed history of travel and recent tick exposure can be useful when evaluating for cytauxzoonosis. A complete blood count, serum blood chemistry, and urinalysis may all be recommended for a baseline evaluation.

Ultimately, the diagnosis will likely be made by identifying the parasitic organism under a microscope from a blood smear (a drop of blood on a slide) or fine-needle aspirate of affected organs (such as liver or spleen). Cytauxzoon felis will appear as a signet-ring-shaped body within the red blood cell. It can look similar to—and occasionally be confused with—other parasites such as Mycoplasma hemofelis or Babesia felis.

Early in the course of the disease, the organism will not be visible in the blood, so repeating the test in 12 to 24 hours is recommended if cytauxzoonosis is suspected.

For confirmation, polymerase chain reaction testing for the presence of the parasite Cytauxzoon felis can be performed on blood or tissue samples.

Treatment of Cytauxzoonosis in Cats

Early diagnosis and aggressive treatment are needed for successful management of cytauxzoonosis. Without treatment, the death rate in domestic cats is nearly 100%, but this drops to around 40 percent with early, intensive therapy.

Cats will need to be hospitalized for IV fluids to correct dehydration and any electrolyte abnormalities, as well as initiating supportive care treatments such as anti-nausea or pain medications, blood transfusions, and nutrition (including feeding tubes and appetite stimulants). The current treatment of choice for Cytauxzoon felis is antiprotozoal therapy with atovaquone and azithromycin, which has shown a 50-60% survival rate.

Recovery and Management of Cytauxzoonosis in Cats

Cytauxzoonosis is deadly in cats, and even with intensive care, only 60% will survive. Typically, those who succumb to the disease do so within the first 24 hours of admission to the ICU. Most cats will remain hospitalized for 7 to 10 days on IV fluids, supportive care, and the antiprotozoal protocol (Atovaquone/Azithromycin).

Cats that survive will recover over the next two to three weeks and are expected to return to normal lives. Most cats that survive acute cytauxzoonosis will remain chronically infected, but clinically asymptomatic for life. They will not need to stay on medications but will never completely be clear of the Cytauxzoon felis infection. This makes them a natural reservoir source for tick transmission, similar to the natural host of the bobcat.

Given the role of ticks in the transmission of cytauxzoonosis, monthly flea and tick prevention are highly recommended. If you live in an area of high prevalence of cytauxzoonosis, it is ideal to keep your cat indoors only to minimize exposure and risk.