Bobcat fever is a tick-borne disease in cats caused by a blood parasite called Cytauxzoon felis. It is one of the deadliest infections a domestic cat can get: without treatment, it kills up to 97% of infected cats. The disease gets its common name because bobcats are the parasite’s natural host, carrying it without getting sick, while domestic cats that pick it up from a tick bite become severely ill within days.
How Cats Get Infected
The parasite spreads through tick bites, primarily from the lone star tick. The American dog tick can also transmit it, though less commonly. A tick picks up the parasite by feeding on an infected bobcat (or, less often, an infected domestic cat that survived a previous bout), then passes it to the next cat it bites.
Clinical signs begin roughly 11 days after a cat is bitten by an infected tick. That gap between the bite and the first symptoms means many owners never connect the illness to a tick encounter, especially if the tick has already dropped off.
Most cases occur between March and September, when ticks are active. The disease is concentrated in the southern, south-central, and mid-Atlantic United States, closely tracking the range of its tick vectors. States like Arkansas, Oklahoma, Missouri, and others across the Southeast report the highest numbers, though the geographic range has been expanding in recent years.
What the Parasite Does Inside a Cat’s Body
Once inside a cat, the parasite invades two types of cells in sequence. First, it infects immune cells called macrophages, which swell dramatically and begin clogging small blood vessels throughout the body. This is the phase that makes bobcat fever so dangerous. Swollen, parasite-filled cells block blood flow to the lungs, liver, spleen, and brain, triggering organ failure.
The parasite also infects red blood cells, destroying them and causing severe anemia. The combination of blocked blood vessels and red blood cell destruction is what makes the disease progress so rapidly and lethally.
Bobcats tolerate this same parasite with minimal illness. Their immune systems keep the infection in check, allowing them to carry the parasite for years as silent reservoirs. Domestic cats that survive infection can also become carriers, creating new sources for ticks to pick up the parasite in neighborhoods far from wild bobcat territory.
Symptoms to Watch For
Bobcat fever hits hard and fast. The earliest signs are nonspecific: your cat stops eating, becomes lethargic, and develops a high fever. Within a day or two, more alarming signs appear. Yellowing of the gums, inner ears, or whites of the eyes (jaundice) is common, along with pale gums from anemia. Cats often breathe rapidly, have a racing heart rate, and may cry out or vocalize from generalized pain.
In advanced cases, cats develop neurological symptoms including uncoordinated movement, seizures, involuntary eye movements, and eventually coma. Some cats go from seemingly fine to critically ill in under 48 hours. Because the early symptoms look like many other illnesses, bobcat fever can be hard to identify without testing, especially if a veterinarian isn’t in a region where the disease is common.
How It’s Diagnosed
Veterinarians can sometimes spot the parasite on a standard blood smear viewed under a microscope, but this method is unreliable, particularly early in the infection when parasite numbers in the blood are still low. PCR testing, which detects the parasite’s DNA, is significantly more sensitive and specific. It can confirm infection even when blood smears look normal.
Blood work typically shows a cluster of abnormalities: anemia that the body hasn’t yet started to correct, low white blood cell counts, low platelet counts, elevated liver enzymes, and high bilirubin levels (a marker of red blood cell destruction). Together with the cat’s history, location, and season, these findings point strongly toward bobcat fever even before PCR results come back.
Treatment and Survival Rates
For decades, bobcat fever was considered a near-certain death sentence. The combination of two antiparasitic drugs, atovaquone and azithromycin, changed the outlook meaningfully. This treatment has reduced the mortality rate from 97% to about 40%. That still means roughly 4 in 10 treated cats don’t survive, but it represents a dramatic improvement over the era when virtually no cats pulled through.
Treatment is most effective when started early, before organ failure sets in. Cats typically need hospitalization for aggressive supportive care alongside the antiparasitic drugs. This includes intravenous fluids, nutritional support, pain management, and sometimes blood transfusions for severe anemia. Recovery takes days to weeks depending on how advanced the disease was at diagnosis.
Cats that survive can remain carriers of the parasite for life. They generally feel fine and show no ongoing symptoms, but they serve as a potential source of infection if a tick feeds on them and then bites another cat.
Preventing Bobcat Fever
Because there is no vaccine, prevention comes down to one thing: keeping ticks off your cat. Newer tick preventatives in the isoxazoline class have shown strong efficacy against the lone star tick specifically. Products containing sarolaner (available in combination formulas for cats) and esafoxolaner have demonstrated 92% to 100% preventive efficacy against lone star ticks for at least one month after application.
If you live in or travel to the southern or south-central U.S. and your cat goes outdoors, year-round tick prevention is essential, with extra vigilance from March through September. Keeping cats indoors eliminates the risk almost entirely, since the disease requires a tick bite to spread. It cannot pass directly from cat to cat.
Checking outdoor cats for ticks daily also helps. The lone star tick needs time attached to a cat’s skin to transmit the parasite, so finding and removing ticks promptly reduces the chance of infection, though it’s not a substitute for chemical prevention.