About 10 days after an infected lone star tick starts feeding, a cat can go from normal to a 106°F fever, yellow gums and open-mouth breathing, and untreated most die within 2–3 days of that peak. This is cytauxzoonosis, also called bobcat fever, and it is not a rare curiosity: a Kansas survey of 1,104 healthy cats found 25.8% carrying the parasite. The difference between a dead cat and a live one is usually measured in hours at the clinic, not in dollars.
What the parasite does in the first 10 days
A tick injects sporozoites into the bite wound. They enter macrophages and become schizonts that swell from roughly 15 µm to 250 µm, large enough to see on a lymph node aspirate. When they rupture, merozoites invade red blood cells, with parasitemia usually 1–4%. The kill mechanism is not the anemia but the plumbing: schizont-packed cells plug small vessels in lung, liver, spleen and brain, producing ischemia, disseminated intravascular coagulation and shock. Incubation runs 5–14 days, about 10 on average, and experimental infections have produced signs as early as 36–48 hours after heavy infestation. Before 2000 the quoted mortality was close to 100%.
Where and when the risk actually concentrates
Cases are reported across 17 states, from Missouri and Arkansas to Florida, Texas, Oklahoma, the Carolinas, Virginia, Illinois and Nebraska. The vector is Amblyomma americanum, the lone star tick; Dermacentor variabilis transmits it only weakly. Oklahoma recorded 232 cases between 1995 and 2006 on a bimodal curve: April–June, then an August–September bump, peaking in May and September, with cases in every month except December. Risk climbs in wooded, low-density housing next to unmanaged land where ticks and bobcats overlap, and Kansas cases skew toward owned male cats over 1 year.
The 36-hour rule turns the tick check into the treatment
Transmission is not instant. Experimental work puts the minimum attachment time at 36 hours, so a tick found on a morning check is close to harmless, while a grey, pea-sized one has been feeding for days. In season, check six places daily: inside the ears, under the chin, around the neck, the armpits, between the toes and the tail base. Pull straight out with fine tweezers using the 3-second removal method, without squeezing the abdomen or pre-treating with alcohol. Dog spot-ons are not a substitute; use a cat-labelled product.
Signs that mean today, not tomorrow
The early picture is vague — lethargy, hiding, refusing food — which is why the numbers below matter more than the mood of the cat. A 104–106°F fever with no other explanation in a cat with outdoor access is cytauxzoonosis until proven otherwise.
| What you see | What it means | Timing |
|---|---|---|
| Fever 104–106°F (40–41°C) | Schizonts loading the vasculature | 5–14 days after the bite |
| Yellow gums, yellow skin | Bilirubin from red cell destruction | Often 24–48 hours after fever starts |
| Pale gums, PCV dropping under 20% | Anemia, later non-regenerative | Day 2–4 of illness |
| Breathing over 40/min at rest | Pulmonary schizont thrombi | Poor prognosis marker |
| Temperature under 99°F (37°C) | Terminal shock | Hours, not days |
Pale gums are the one sign owners can grade at home; the three mucous membranes take 20 seconds and give the vet a baseline.
Diagnosis: three tests and the numbers they return
The CBC is the fastest clue: leukopenia with toxic neutrophils, thrombocytopenia, non-regenerative anemia, hyperbilirubinemia and low albumin; one study found DIC in 5 of 5 acute cases. On a stained smear, piroplasms are 0.8–2.2 µm rings with a pale centre sitting in 1–4% of red cells, and they typically appear only 1–3 days before death, so a clean smear proves nothing. Fine-needle aspiration of an enlarged lymph node or spleen can show 15–250 µm schizonts earlier. PCR is the most sensitive test and must be drawn before the first atovaquone dose.
Treatment: 10 days, two drugs, one clock
The published protocol is atovaquone at 15 mg/kg by mouth every 8 hours plus azithromycin at 10 mg/kg once daily, both for 10 days; the treating veterinarian sets the exact dose. In an 80-cat randomised trial this combination saved 60% versus 26% for a single imidocarb injection; a large case series reported 64%. Supportive care carries as much weight: IV fluids, heparin 100–200 U/kg under the skin three times a day, oxygen, a transfusion if the PCV collapses, and a feeding tube for the oral drugs. Keep handling minimal and the cage quiet; fever usually breaks in 5–7 days and blood work normalises over 2–3 weeks.
What the bill looks like
Cost is dominated by ICU time, not the antiprotozoal: published estimates for a full course run from about $500 to $5,000, tracking how many nights the cat spends on fluids.
| Item | Typical range (USD) |
|---|---|
| Emergency exam, CBC and chemistry | $200–400 |
| PCR confirmation | $100–200 |
| Atovaquone, 10-day compounded course | $80–300 |
| Azithromycin, 10 days | $20–60 |
| ICU hospitalisation, 3–7 days | $1,500–4,000 |
| Blood transfusion, if needed | $200–400 |
The arithmetic: a 4 kg cat needs 60 mg per dose, 180 mg a day, 1.8 g for the whole course. The human suspension is 750 mg per 5 mL, so the entire treatment is 12 mL — while a 300 mL bottle retails near $930 and even discounted costs $170–210. Compounded capsules avoid paying for 288 mL the cat will never take. Annual tick prevention is cheaper; monthly versus quarterly control is a $60–200 decision.
Prevention that has trial numbers behind it
There is no vaccine. An imidacloprid 10%/flumethrin 4.5% collar blocked transmission in all 10 treated cats exposed to infected ticks; ticks fed on all 10 controls and 9 became infected. A topical selamectin 6 mg/kg plus sarolaner 1 mg/kg product left 0 of 8 treated cats positive against 7 of 8 controls, with over 94.7% efficacy against lone star tick infestation across 3 consecutive months. Neither replaces checks: CAPC ranks year-round acaricide plus indoor living as the core strategy, with brush cleared and grass cut short. In an endemic state, fever makes tick paralysis and this disease both same-day problems.
If your cat survives, it is a carrier for life
Survivors clear their signs within 2–3 weeks, but most stay chronically parasitemic and symptom-free. No protocol eliminates the parasite, and survivors must never be blood donors: transfusion passes the red-cell stage. Keep tick control going, because immunity is strain-specific.
The short version: a fever over 104°F in a cat with outdoor exposure is a same-day problem in the south-central and south-eastern United States, and the smear may be negative on day one.
This article is for information and does not replace a veterinary diagnosis. Cytauxzoonosis is fatal within days without treatment; if your cat has a high fever, yellow gums or laboured breathing, call an emergency hospital now rather than waiting for an appointment.
Terms mentioned in this article
Frequently asked
Can an indoor-only cat get cytauxzoonosis?
It happens, but it is uncommon. Ticks hitch rides on dogs, clothing, cut grass and visiting people, and a tick needs 36 hours of attachment to transmit, so a tick found the same evening is usually harmless. Merck still calls indoor living the single best prevention, which tells you how much weight to give the door.
How soon after a tick bite would a cat get sick?
Signs appear 5 to 14 days after transmission, about 10 days on average, and experimental heavy infestation has produced illness in 36 to 48 hours. Because the delay is that long, the tick is usually gone by the time the cat has a fever, so not finding a tick proves nothing either way.
Is it contagious to other cats or to people?
No cat-to-cat spread has been shown without a tick, and the parasite is not known to infect people; dogs and other species are not affected, because infection is limited to felids. The one exception is blood: transfusing from a survivor can pass the red-cell stage and cause a mild infection.