Feline leukemia virus (FeLV) spreads through prolonged, close contact between cats — mutual grooming, shared food bowls, bite wounds, a mother cat nursing kittens — not through a single sniff at the fence or a quick hiss-and-back-away encounter at the shelter. It’s one of the leading infectious causes of death in cats, but it’s also one of the easiest to test for and prevent. A same-day blood draw tells you where your cat stands, and a vaccine exists if your cat’s lifestyle puts them at risk.
How cats actually get FeLV
FeLV is a retrovirus, meaning it inserts itself into the host’s DNA — which is part of why it’s so persistent once established. It’s shed in saliva, nasal secretions, urine, feces, and milk, and it doesn’t survive long outside a cat’s body, so casual environmental contact (a shared yard, a fence line, a human’s hands) isn’t a realistic transmission route.
The virus needs sustained, close contact to spread efficiently. That means the highest-risk situations are:
- Mutual grooming between cats who live together
- Shared food and water bowls over time
- Bite wounds from fighting, particularly relevant for unneutered outdoor toms
- Mother-to-kitten transmission, in utero or through nursing
This is why FeLV shows up disproportionately in cats from multi-cat households with unknown vaccination histories, free-roaming or previously stray cats, and kittens from unscreened litters. A single indoor cat with no exposure to other cats is at very low risk. The American Association of Feline Practitioners (AAFP) estimates FeLV infection in roughly 2–3% of cats in the US, with prevalence climbing several times higher in cats that are sick, stray, or living in group settings.
The symptoms are easy to miss at first
FeLV doesn’t cause one signature illness — it works by suppressing the immune system and, in some cats, triggering cancers like lymphoma. That means the symptoms owners actually see are usually secondary: the infections and conditions a healthy immune system would normally fend off.
Watch for:
- Recurring infections (skin, respiratory, urinary) that keep coming back
- Pale gums, which can point to FeLV-related anemia
- Progressive weight loss and poor appetite
- Enlarged lymph nodes
- Chronic diarrhea
- Poor coat condition and lethargy
- Reproductive problems in unspayed females (infertility, abortion)
Some cats carry FeLV for months or years with no obvious symptoms before their immune system starts losing ground — which is exactly why testing matters more than watching and waiting.
Testing: one blood draw, two different tests
Most vets start with an ELISA (enzyme-linked immunosorbent assay) test, which checks blood for FeLV antigen and can be run in-clinic with results in minutes. A positive ELISA doesn’t automatically mean lifelong infection, though — some cats mount an effective immune response and clear the virus within weeks, particularly if they’re tested and isolated early.
Because of that, a positive ELISA is typically followed by a confirmatory IFA (immunofluorescent antibody) test, usually sent to an outside lab, which checks for a more advanced stage of infection in bone marrow. A cat who is IFA-positive is considered persistently infected.
The AAFP recommends testing any cat with an unknown status before introducing them to other cats, any sick cat regardless of history, and all kittens before they’re vaccinated or allowed contact with other cats in the home.
Vaccination and prevention
There is an FeLV vaccine, and the AAFP classifies it as a “non-core” vaccine — meaning it’s recommended based on lifestyle rather than given to every cat automatically. It’s specifically recommended for kittens (since risk is highest early in life and initial vaccination series typically happens before lifestyle is fully established) and for any cat with outdoor access or exposure to cats of unknown status.
A strictly indoor-only cat living alone or with other tested, negative cats has minimal ongoing risk and may not need continued boosters after the kitten series — this is a conversation to have with your vet based on your specific household. How Often Should You Take Your Cat to the Vet? A Life-Stage Guide is a useful starting point for figuring out your cat’s overall preventive care schedule, vaccines included.
Beyond vaccination, the most effective prevention is testing before introduction: any new cat entering a multi-cat household should be tested and, ideally, kept separated until results come back. Spaying and neutering also reduces risk indirectly, since it curbs the roaming and fighting behavior that spreads the virus most efficiently.
Life with an FeLV-positive cat
A positive diagnosis isn’t an immediate emergency, and it isn’t a death sentence in the way it was often treated decades ago. Persistently infected cats can live for years — the median survival estimates in older literature (often cited as 2–3 years post-diagnosis) are frequently more pessimistic than what vets now see with good supportive care, since FeLV management has improved and average survival varies enormously by individual cat.
Practical management looks like:
- Keeping the cat strictly indoors, both to protect them from other infections and to prevent transmission to other cats
- Twice-yearly vet visits instead of annual, since early detection of secondary infections matters more
- Prompt treatment of any illness rather than a wait-and-see approach
- Keeping other cats in the household FeLV-negative and vaccinated, or maintaining separation if that’s not possible
FeLV-positive cats are sometimes confused with FIV-positive cats, but the two are different viruses with different transmission patterns and different outlooks — worth understanding separately if you’re navigating a mixed-status household. FIV in Cats: What It Means and How to Care for a Positive Cat covers the comparison in more depth.
When to see a vet
Get your cat tested promptly if any of the following apply:
- You’re adopting a cat or kitten of unknown FeLV status
- Your cat has recurring infections, unexplained weight loss, pale gums, or persistent lethargy
- Your cat has been in a fight or bitten by an unknown cat
- You’re introducing a new cat into a household with existing cats
If your cat already has a confirmed positive diagnosis, any new symptom — reduced appetite, labored breathing, sudden lethargy — warrants a same-week vet visit rather than a wait-and-see approach, since a suppressed immune system gives infections much less resistance to work against.
The bottom line: FeLV is manageable, testing is simple, and vaccination is a real option for at-risk cats. The virus is scarier in the abstract than it usually is in practice once you know a cat’s status and plan around it.