A cat that tests FeLV positive has been exposed to feline leukemia virus, a contagious virus that affects the immune system and bone marrow. But a positive test result doesn’t automatically mean your cat is sick or will become sick. How the virus affects your cat depends on which type of infection develops, and roughly 30 to 40% of exposed cats fight off the worst of it on their own.
How FeLV Infects a Cat’s Body
Feline leukemia virus typically enters through the mouth and throat, often through close contact with an infected cat’s saliva during grooming, sharing food bowls, or bite wounds. From there, the virus moves into the tonsils and nearby lymph nodes, where it begins replicating. Infected immune cells then carry the virus through the bloodstream in what’s called a primary viremia, essentially the first wave of virus circulating in the blood.
What happens next determines everything. If the virus reaches the bone marrow and begins infecting the cells that produce white blood cells and platelets, a second, persistent wave of infection takes hold. This is when the virus becomes deeply embedded and much harder for the immune system to control. Not every cat reaches this stage, though, and that’s where the different infection categories come in.
Three Types of FeLV Infection
Not all FeLV-positive cats have the same prognosis. After exposure, a cat’s immune system responds in one of three main ways.
Progressive Infection
About 30 to 40% of exposed cats develop a progressive infection. Their immune system fails to stop the virus from establishing itself in the bone marrow, leading to persistent virus in the bloodstream. These cats actively shed the virus and can infect other cats. They are the ones most likely to develop serious FeLV-related illness, including cancer, severe anemia, and immune suppression. Kittens are at much higher risk of progressive infection than adult cats exposed to the same virus.
Regressive Infection
Another 30 to 40% of cats mount a partially effective immune response. They clear the virus from the bloodstream but can’t fully eliminate its DNA, which remains embedded in cells in the bone marrow. These cats are not contagious to other cats during this stage and are very unlikely to show clinical signs of disease. Their life expectancy is similar to that of uninfected cats. However, the virus can reactivate later if the cat’s immune system becomes weakened by illness or certain medications.
Abortive Infection
An estimated 20 to 30% of exposed cats eliminate the virus entirely before it incorporates into their DNA. These cats develop antibodies and are considered immune. They will never test positive on routine screening tests and will never show signs of disease, so most owners never know the exposure happened at all.
What a Positive Test Actually Tells You
The standard screening test used at most veterinary clinics detects a viral protein circulating in the blood. A positive result on this initial test means the virus is currently active in the bloodstream, but it doesn’t distinguish between a cat in the early stages of fighting off the virus and one with a permanent progressive infection. That’s why confirmatory testing matters.
Your vet may recommend a second type of blood test that checks whether the virus has reached the bone marrow, or a DNA-based test that looks for the virus’s genetic material integrated into cells. These additional tests help determine whether your cat has a progressive infection (persistent and serious) or a regressive one (contained and manageable). A single positive screening result, especially in an otherwise healthy cat, is not a final answer.
False positives are uncommon but do occur. One large study found that roughly 1 in 283 cats produced a false-positive result on the standard blood test due to interfering antibodies in the sample. Retesting four to six weeks later helps rule out both false positives and early infections that the cat’s immune system may still be fighting off. This waiting period is especially important for kittens, whose immature immune systems may take longer to respond.
Health Risks of Progressive FeLV
Cats with progressive FeLV face three main categories of disease. The virus weakens the immune system, making cats vulnerable to infections they would normally fight off easily. It disrupts blood cell production in the bone marrow, leading to anemia and low platelet counts. And it increases the risk of certain cancers, particularly lymphoma.
The prognosis for progressive infection is sobering. One survival study found a median survival time of just 30 days after diagnosis for cats with progressive FeLV, though the mean survival was about 141 days, meaning some cats lived considerably longer. By contrast, cats with regressive infections had a mean survival exceeding 490 days, and researchers noted their life expectancy was comparable to uninfected cats. The wide gap between these numbers underscores why identifying the type of infection is so important.
Living With an FeLV-Positive Cat
If your cat has a confirmed progressive infection, keeping them indoors is essential. This protects other cats from exposure and protects your cat from picking up secondary infections their weakened immune system can’t handle. If you have other cats in the home, they should be tested and vaccinated, and ideally separated from the positive cat to prevent transmission through grooming, shared bowls, or litter boxes.
FeLV-positive cats should still receive their routine vaccinations. The American Association of Feline Practitioners specifically recommends against skipping vaccines in these cats, because their compromised immune systems make them more vulnerable to severe illness from common infections like panleukopenia and upper respiratory viruses. Vaccine schedules should follow the same risk-based guidelines used for any cat.
More frequent veterinary checkups help catch complications early. Many vets recommend visits every six months rather than annually for FeLV-positive cats, with bloodwork to monitor for anemia and changes in white blood cell counts. Weight loss, persistent lethargy, recurring infections, pale gums, or swollen lymph nodes are all signs that warrant a prompt visit.
Protecting Other Cats
FeLV spreads primarily through saliva, so prolonged close contact is the biggest risk factor. Cats that groom each other, share food and water dishes, or fight are most likely to transmit the virus. Casual or brief contact poses a much lower risk, and the virus is fragile outside the body, surviving only minutes in the environment.
Vaccination is highly effective at preventing infection. In one controlled study, 17 out of 18 vaccinated cats were protected against persistent infection after direct exposure, compared to only 2 out of 12 unvaccinated cats. The vaccine is recommended for all kittens and for any adult cat with potential exposure to FeLV-positive cats, including those that go outdoors or live in multi-cat households with unknown FeLV status.
Every new cat entering a household should be tested before being introduced to resident cats, regardless of how healthy they appear. Cats with regressive infections look and feel perfectly normal but still carry viral DNA that could theoretically reactivate, making testing the only reliable way to know a cat’s status.