Feline Leukemia (FeLV): One Virus, Three Very Different Outcomes

Feline leukemia virus is the diagnosis owners fear most, and the name does it no favors. Here is the fact that reorganizes everything else on this page: exposure to FeLV is not one outcome. It is three, and they differ so much that one of them shortens a life dramatically while another may never matter at all. The test result that starts the conversation is not the end of it.

FeLV is a retrovirus, a family of viruses that write themselves into a cat's own genome. Cornell's feline health center states the practical consequence plainly: the virus can be incorporated into the cat's DNA, which is why "cured or not" is the wrong frame and "which outcome" is the right one. Outside a cat's body the virus is fragile, surviving "probably less than a few hours under normal household conditions" in Cornell's words. It infects cats only. People and dogs are not at risk.

How cats catch it

The virus travels in saliva above all, and also in nasal secretions, urine, feces and milk. The routes are intimate ones: mutual grooming, shared food and water bowls, shared litter boxes, bite wounds, and a mother nursing her kittens. Kittens can be infected before birth or through milk, and they are the most vulnerable group by far. The other grave disease of young cats, FIP, is unrelated but shares exactly this youth skew.

Two practical consequences follow. First, a cat that goes outdoors and meets unfamiliar cats carries a real exposure risk, while a solitary indoor cat carries very little. Second, the incubation is long: Cats Protection notes that months or sometimes years can pass between infection and the first signs, which is why testing exists at all.

The three outcomes, with their real numbers

When a cat meets FeLV, its immune system decides what happens next, and the modern testing vocabulary splits the result into categories. Cornell's ranges for exposed cats: at least 20 to 30% develop an abortive infection and eliminate the virus outright. About 30 to 40% develop a regressive infection: the virus is written into the genome but the immune system pins it down, the cat does not shed virus in any meaningful way, and many of these cats live unremarkable lives. And 30 to 40% develop a progressive infection, where the virus replicates continuously in the bone marrow. Progressive infection is the one the grim statistics describe.

How likely each outcome is depends enormously on who the cat is and where it lives. The cleanest single dataset comes from Australia, where researchers tested two populations side by side in the same 2019 study:

Read that last column twice. Progressive infection was roughly forty times more common in the group-housing population than among healthy owned pets. Housing and exposure, not bad luck, drive most of the risk. A four-country European study using the same categories found overall prevalence ranging from about 9% of tested cats in France and Germany to about 21% in Italy and Portugal, so geography moves the needle too.

Testing: why one test is rarely the whole answer

The in-clinic screening test detects viral antigen, a protein from the virus itself, in blood. It is the right first step and an imperfect last word. The professional guidance is consistent on three points:

• A recent exposure needs a retest. Cornell's guidance: repeat the test 3 to 6 weeks after a possible exposure, and follow up most positive results 6 to 12 weeks later, because early results can change as the infection resolves or settles.
• A positive in a healthy cat deserves confirmation. The European advisory board's guideline is explicit that in low-prevalence areas a positive screening result in a healthy cat should be confirmed, preferably by PCR. The 2025 Australian guidelines say the same for their market: point-of-care positives should be confirmed with PCR for proviral DNA, because false positives occur in low-prevalence settings.
• PCR is what separates the outcomes. Antigen tests see active virus; PCR sees the virus written into the genome. The 2020 American retrovirus guidelines introduced a two-tier system combining a sensitive antigen test with quantitative PCR precisely because that pairing can distinguish a regressive infection from a progressive one, and those two words carry very different futures.

One testing myth needs killing here: the idea that a kitten's maternal antibodies cause false-positive FeLV tests. FeLV screening detects antigen, a piece of the virus, not antibodies. That caveat belongs to FIV testing, which is antibody-based, and the two get conflated all over the internet.

The vaccine question changes with your passport

Whether your cat should be vaccinated against FeLV has a genuinely different official answer depending on the country, and this is one of the sharpest four-market splits we have found on any health topic.

New Zealand, which shares Australia's guideline document, has no FeLV vaccine available at all, so its veterinarians receive no vaccine recommendation whatsoever. Same virus, four rulebooks. Wherever you live, one rule is universal: test before vaccinating, because vaccinating an already infected cat does nothing.

Boosters and the wider schedule belong to our vaccination guide, which covers the laws and the sarcoma question honestly.

What FeLV actually does to a cat

There is no signature symptom. FeLV suppresses the immune system and interferes with the bone marrow, so what owners actually see is the aftermath: weight loss, appetite loss, a coat gone dull, pale gums, sore or inflamed gums, fevers that keep returning, infections that keep returning, enlarged lymph nodes, diarrhea, and in some cats neurological signs or eye disease. The professional shorthand for the serious progressive-infection diseases: acquired immunodeficiency, aplastic anemia, lymphoma and leukemia.

Because none of that is specific, the honest rule is the one this site repeats everywhere: a cat that is off its food, losing weight or repeatedly unwell needs a veterinarian, and the test, not the symptom pattern, answers the FeLV question.

How long do FeLV-positive cats live? Honest numbers, with their populations

Survival statistics for FeLV are quoted everywhere and sourced almost nowhere, so here are the measured ones with their populations attached, because the population is the number.

• Cornell: median survival after diagnosis around 2.5 years, and explicitly longer for regressive infections.
• Merck's manual: average 2.4 years after diagnosis in large studies, with 50% mortality by two years and 80% by three. These figures describe diagnosed, largely progressive infections.
• A 2025 hospital study followed 176 cats and recorded a median survival of just 30 days in its progressively infected group. Before that number frightens you: these were cats already sick enough to be at a referral hospital, and in the same study the regressively infected cats' survival curve was indistinguishable from uninfected controls. The population is the number.
• The 2025 Australian guidelines add the line every anxious owner should hear: cats should not be euthanized because of a positive FeLV test alone, as some remain healthy for years.

You will also meet the claim that FeLV is "the second leading cause of death in cats." We looked for its source and could not find one anywhere: no study, no data year, just the same sentence copied between websites, probably since before modern vaccines existed. We do not repeat it as fact.

Living with an FeLV-positive cat

Two rules carry almost all of the guidance. The first: an FeLV-positive cat lives indoors, both to protect other cats from the virus and to protect an immunosuppressed cat from everything else. The Australian guidelines accept secure outdoor enclosures as an equivalent.

The second is the one most websites blur, and it is where FeLV and FIV part ways completely. The American retrovirus guidelines take opposite positions for the two viruses: FeLV transmits readily enough within a household that FeLV-positive cats should be adopted into homes only with other FeLV-positive cats, or as single cats. FIV, by contrast, transmits so poorly between stable, neutered housemates that mixed FIV households are considered low-risk. If you have absorbed the "retrovirus cats can live with anyone" idea, it comes from FIV guidance, and it does not carry over. Our FIV guide covers that half of the story.

Beyond that: keep the cat fully vaccinated against everything else, feed a complete diet, skip raw feeding for an immunosuppressed animal, and see the vet at the first sign of trouble rather than the fifth.

Treatment, honestly

There is no cure for FeLV, and every reputable body says so in those words. Supportive and symptomatic care is real care: secondary infections are often treatable, and treated cats can feel well for long stretches.

One genuine four-market wrinkle: an antiviral immune modulator, recombinant feline interferon omega, is licensed for FeLV treatment in Europe, Japan and Australia. It has no US approval, so American owners reading European sites may be offered hope their own vet legally cannot prescribe. Evidence for it is modest and your vet's judgment governs. For FeLV-associated lymphoma, chemotherapy protocols exist and buy real time for some cats; that conversation belongs with an oncologist.

What to take away

• Feline leukemia virus spreads through friendly, everyday contact: mutual grooming, shared bowls and litter boxes, and a mother nursing her kittens; kittens are by far the most vulnerable.
• One virus, three outcomes (abortive, regressive, progressive), and only testing tells you which one you are looking at.
• A positive in-clinic screen in a healthy cat calls for a confirmatory PCR test, not a verdict; FeLV screening detects antigen, so maternal antibodies do not cause kitten false positives (that caveat belongs to FIV).
• The US guidelines make the FeLV vaccine core for every kitten (two doses from 8 weeks), then risk-based after age one; Australia's 2025 guidelines reserve it for demonstrable exposure risk.
• Cohabitation advice is the opposite of FIV's: FeLV-positive cats belong in FeLV-positive or single-cat homes, indoors.
• A positive diagnosis, even progressive, is a management plan (six-monthly checks, prompt attention to any infection), not an immediate goodbye.