What is feLV (feline leukaemia virus)?
Updated By PetymFacts checked against official sources on
Quick answer
FeLV, feline leukaemia virus, is a virus of cats that weakens the immune system and can cause anaemia and cancers. It spreads through close contact: saliva in grooming, shared bowls and litter trays, bites, and from mother to kitten. Kittens are most at risk. A test comes before the vaccine, which reduces risk but is not complete protection.
Also called FeLV, feline leukaemia virus, feline leukemia virus, feline leukaemia.
Key facts
- FeLV spreads through saliva, faeces, urine and milk: bites, grooming, shared bowls and litter boxes, and from mother to kittens. Cornell University College of Veterinary Medicine
- Outside the body the virus probably survives less than a few hours in ordinary household conditions. Cornell University College of Veterinary Medicine
- Kittens are much more likely than adults to develop a progressive infection. Cornell University College of Veterinary Medicine
- The median survival after diagnosis is about 2.5 years, and can be much longer for cats with a regressive infection. Cornell University College of Veterinary Medicine
- WSAVA calls FeLV vaccine core where FeLV is common, for cats under 1 year and adults that go outdoors or live with cats that do. WSAVAstudy
How does FeLV spread?
FeLV needs close, friendly contact. Cats that groom each other, share food and water bowls and use the same litter tray pass it in saliva and other body fluids, and an infected mother can pass it to her kittens. Bites spread it too. Because the virus dies within hours outside the body, it does not linger in a room the way panleukopenia does.
Petym found no published study of how common FeLV is in Indian cats, and ICAR-IVRI's vaccine leaflet does not list the vaccine. The risk is highest for kittens and for cats that mix with unknown cats outdoors or in a multi-cat home.
What do progressive, regressive and abortive infection mean?
A cat exposed to FeLV can go one of three ways. Follow-up tests 6 to 12 weeks apart help tell them apart.
- Progressive infection
- The virus keeps multiplying. The cat can infect others and is at high risk of fatal FeLV-related disease. Cornell estimates 30 to 40% of exposed cats go this way. Cornell University College of Veterinary Medicine
- Regressive infection
- The immune system holds the virus in check. It is absent from the blood, the cat is unlikely to show signs, but the virus can reactivate in illness or stress. Cornell University College of Veterinary Medicine
- Abortive infection
- The immune system clears the virus completely. At least 20 to 30% of exposed cats may do this. Cornell University College of Veterinary Medicine
What are the signs of FeLV?
Early infection often shows no signs at all. Later, a cat may lose weight and appetite, have a dull coat, swollen lymph nodes, a lasting fever, pale gums, a sore mouth, repeated infections, diarrhoea, or eye and nerve problems. These signs overlap with many other illnesses, so only a vet's tests can confirm FeLV.
How is FeLV prevented?
Keep cats indoors or supervise outdoor time, test any new cat before it joins the home, and never share bowls or trays between infected and uninfected cats. A cat must test negative before it is vaccinated. WSAVA's schedule is two doses from 8 weeks, 3 to 4 weeks apart, then a booster a year later, with later boosters set by the cat's risk.
Cornell notes that the vaccine reduces risk but will not protect every cat. Your vet decides whether your cat needs it.
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Questions owners ask
How is FeLV tested?
- Usually with a blood test at the clinic that screens for the virus, confirmed with another test at a laboratory. No single test tells the whole story: a cat exposed recently may need a retest after 3 to 6 weeks, and a follow-up 6 to 12 weeks later shows whether an infection is progressive or regressive.
Does my indoor cat need the FeLV vaccine?
- WSAVA calls the FeLV vaccine core where FeLV is common for cats under 1 year, and for adults that go outdoors or live with cats that do. A cat that stays indoors alone may not need it. A negative test comes first. Your vet decides.
How long can a cat live with FeLV?
- Cornell gives a median survival of about 2.5 years after diagnosis, and much longer for cats with a regressive infection, where the immune system keeps the virus in check. Indoor living, regular vet checks and quick treatment of infections help an FeLV positive cat stay well longer.
Can an FeLV positive cat live with a negative cat?
- It is risky, because FeLV spreads through grooming and shared bowls and litter trays. Cornell advises testing all cats in the home and separating infected from uninfected cats. If they must share a home, ask your vet about vaccinating the negative cat and keep their bowls and trays apart.
Keep reading
Related terms
More in health conditions
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- Bloat (GDV)Bloat, or gastric dilatation-volvulus (GDV), is when a dog's stomach fills with gas and twists on itself, cutting off its blood supply. It mainly affects large and giant deep-chested breeds. Unproductive retching, a swelling belly, drooling and restlessness are the signs. It is a surgical emergency that can kill within hours.
- BOASBOAS, brachycephalic obstructive airway syndrome, is a breathing disorder of flat-faced dogs. Narrow nostrils, an overlong soft palate and a small windpipe block airflow, so affected dogs snore, snort, tire quickly and overheat easily. It is worse in heat, humidity and obesity. Surgery can widen the airway, and a lean weight helps.
- Canine distemperCanine distemper is a serious viral disease of dogs that can attack the skin, airways, gut and nervous system. It spreads in droplets from coughing, sneezing and barking, and through body fluids. There is no specific cure, and some dogs do not survive even with treatment. The D in the DHPPi vaccine prevents it.
- Canine parvovirusCanine parvovirus, or parvo, is a highly contagious virus that attacks a dog's gut and immune system. It spreads through infected faeces, survives a long time in the environment and hits unvaccinated puppies between 6 weeks and 6 months hardest. Vomiting and bloody diarrhoea can kill within days, and it is prevented by the core vaccine.
- Cat fluCat flu is the everyday name for an upper respiratory infection in cats. More than 90% of cases are caused by feline herpesvirus, feline calicivirus or both. Cats sneeze, have runny eyes and nose and may stop eating. Most recovered cats remain carriers, and stress can bring the virus back. Vaccination usually prevents severe disease.
- Cherry eyeCherry eye is when the tear gland inside a dog's third eyelid slips out of place and shows as a smooth, red, cherry-like lump in the inner corner of the eye. It is common in young Bulldogs, Beagles, Shih Tzus and Pugs, and needs a vet, usually for surgery to put the gland back.
- Chronic kidney diseaseChronic kidney disease (CKD) is a slow, lasting loss of kidney function, common in older cats and also seen in older dogs. Early on there are often no signs; later a pet drinks and urinates more, eats less and loses weight. It cannot be cured, but a kidney diet, water and regular checks can slow it.
- DehydrationDehydration means a pet's body has lost more water than it has taken in, through heat, panting, vomiting, diarrhoea or illness. Early on the gums turn sticky; then the skin loses its spring and the eyes sink. A mildly dehydrated pet needs water and a watchful eye; a weak, vomiting or collapsing one needs a vet now.
- Dental diseaseDental disease in pets is mostly periodontal disease: plaque bacteria inflame the gums (gingivitis) and then destroy the tissue and bone holding the teeth (periodontitis). It is the most common disorder vets diagnose in dogs, and very common in cats. Bad breath, tartar and red gums are the early signs. Daily brushing prevents most of it.
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Sources
Each source was opened and read on the date shown. How Petym checks its sources
- Cornell University College of Veterinary Medicine: Feline leukemia virus (Cornell Feline Health Center) (opens in a new tab)
- European Advisory Board on Cat Diseases (ABCD): Guideline for feline leukaemia virus infection (opens in a new tab)
- WSAVA: Core and non-core vaccines for pet cats (opens in a new tab)
- ICAR-IVRI: Vaccination of dogs and cats (Hindi leaflet, 2020) (opens in a new tab)
- WSAVA: 2024 guidelines for the vaccination of dogs and cats (WSAVA Vaccination Guidelines Group, Journal of Small Animal Practice) (opens in a new tab)