Cytauxzoonosis – The Dangers of Bobcat Fever in Cats

In Diaries of a Veterinarian, my human mom, Dr. Dunn, discusses life as a vet, gives vet tips, and discusses all things vet related as a guest on my blog. 

If you live in the southern, central, or mid-Atlantic areas of the  United States and own a cat, you should be aware of the potentially deadly disease, Cytauxzoonosis (or bobcat fever). Cytauxzoonosis (pronounced Sight-oh-zo-un-osis) is a life-threatening disease of domestic cats. It is caused by the protozoal parasite, Cytauxzoon felis.. The disease progresses rapidly and has an extremely high mortality rate. No vaccines are available. Therefore, all cat owners should be aware of this devastating disease and how to best protect their furry companion.

Transmission of Cytauxzoonosis

Bobcat fever gets its nickname because a bobcat serves as the natural host of infection. After an infected host is bitten by a tick, the C. felis parasite begins a process of reproduction inside the tick. The infected tick then bites a domestic cat, leading to infection. Bobcats do not become ill when infected with the parasite. However, infection often proves fatal to domestic cats.

What Happens When a Cat Gets Infected? 

About 5-14 days after an infective tick bite, the cat will begin to show signs of illness. The first stage of infection (tissue stage – schizont) occurs when the parasite infects immune cells that line blood vessels. These cells become enlarged and block blood flow to the infected organs. Multi-organ failure results. This phase leads to the most profound signs of illness. These enlarged cells will rupture, releasing tiny merozoites into the bloodstream. These tiny organisms infect the red blood cells, leading to the erythrocytic phase.

Clinical Signs and Diagnosis

The first signs of illness are typically non-specific. The cat may be less playful with a slightly decreased appetite. However, the disease progresses very rapidly. Infected cats will quickly spike an extremely high fever. Rapid breathing and pale or yellow gums are also frequent findings. In later stages of illness, the temperature will drop below normal. The cat will frequently yowl in pain. These later signs typically indicate a grave prognosis.

It should be noted that just because a tick is not visible on a cat doesn’t mean it can’t be infected. As mentioned previously, the tick bite may have occurred up to two weeks prior. Also, cats are very fastidious groomers. They often remove ticks before the owners have a chance to notice them.

Diagnosis of bobcat fever is not always straightforward. A presumptive diagnosis is often made based on clinical signs. In a patient suspected of cytauxzoonosis, the veterinarian may need to perform multiple tests to check for infection and to rule out other diseases. In the later erythrocytic phase of the disease, the tiny parasite can often be seen within red blood cells under the microscope. However, during the first tissue phase, these tiny inclusions are often not present. Send-off tests or lymph node aspirates can sometimes yield a diagnosis. However, in cats that are strongly suspected to be infected, aggressive treatment is often begun before a definitive diagnosis is made. The blood then is rechecked in a few days to confirm the diagnosis.

Treatment

Until recent years, cytauxzoonosis was considered nearly 100% fatal. A newer treatment protocol has been developed that includes a combination of the antibiotic, Azithromycin, and the anti-malarial drug, atovaquone. The cat will be hospitalized with IV fluids. Injections to decrease blockages in the blood vessels are indicated. The cat will also receive supportive care, including pain medication and nutritional support as needed.

Without early and aggressive treatment, the prognosis is grave. Even in patients treated right away, the prognosis is guarded.

How Can Bobcat Fever Be Prevented?

Unfortunately, there is no way to prevent cytauxzoonosis in 100% of animals. However, since a tick must bite a cat to lead to infection, tick prevention is the most important part of protecting a pet. Cats should be kept indoors during peak tick season (from early spring through late fall). All animals in the house with access to the outdoors need to be kept on a strict regimen of tick preventatives.

Regardless of whether or not a cat has access to the outdoors, they should receive an effective tick product as recommended by the veterinarian. Unfortunately, cats don’t have as many options for tick prevention as dogs do. An open discussion with the primary care veterinarian is warranted to determine which option is best. Currently, the most popular products are Frontline Gold (applied monthly) and a Seresto Collar (applied at least every eight months).

In cats, as with all animals, many illnesses can have similar clinical signs. Therefore, it is extremely important that owners pay attention to subtle changes in their pet’s behavior. With immediate veterinary care, cats infected with this often-fatal disease may have a chance of survival.