Feline Leukemia (FeLV): Signs, Testing and Prevention

What it is and how cats catch it

FeLV is a retrovirus that only infects cats. Cornell Feline Health Center estimates that about 2 to 3 percent of cats in the United States carry it, rising to as many as 30 percent among cats that are sick or at high risk. The virus is shed mainly in saliva and also in nasal secretions, urine and feces, so it passes during mutual grooming, sharing bowls and litter boxes, bite wounds and mating. A mother cat can pass it to her kittens before birth or while nursing.

The virus is fragile and survives only a few hours outside a cat, so it is not usually picked up from the environment. The cats most at risk are kittens, cats that roam outdoors and fight, and cats living with an infected cat or one whose status is unknown. Exposure does not always lead to lasting infection: some cats clear the virus, some keep it hidden in their cells without spreading it, and some develop a progressive infection with continuous virus in the blood, which carries the poorest outlook.

Signs of feline leukemia

Early on there are often no signs at all. When illness develops, it tends to reflect a weakened immune system and damaged bone marrow. Common signs include gradual weight loss, poor appetite, a dull or unkempt coat, enlarged lymph nodes, fever that comes and goes, pale gums from anemia, inflamed gums and mouth, and infections of the skin, bladder or airways that keep returning or are slow to heal.

Other cats develop persistent diarrhea, eye problems, nervous system signs such as wobbliness or behavior changes, or reproductive problems. Cornell describes FeLV as the most common cause of cancer in cats, with lymphoma the best known. None of these signs is unique to FeLV, which is why your vet will test rather than assume.

When to call your vet today

Book a visit promptly if your cat has lost weight, is eating less, has had several infections in a row, has a fever, or has gums that look paler than usual. Call too if your cat was recently bitten by or lived with a cat that has tested positive, or if you have just adopted a cat or kitten whose status is unknown.

If your cat is already known to be FeLV positive, call your vet early for any change at all, such as a few days of poor appetite, sneezing, a sore mouth or hiding. Because their immune system is weaker, infections that a healthy cat would shrug off need attention sooner.

When it's an emergency

Go to your vet or the nearest emergency vet immediately if your cat has very pale or white gums, is breathing fast or with effort, collapses, is extremely weak, has not eaten for more than a day or two, or has a seizure. Severe anemia and fluid around the chest from lymphoma can both cause breathing difficulty and need urgent care.

Bleeding that will not stop, a sudden inability to walk, or a cat that is cold, limp and unresponsive are also emergencies. Keep your cat warm and quiet and call ahead while you travel.

What you can safely do at home

Keep an FeLV-positive cat indoors, both to protect it from infections and to stop it spreading the virus to other cats. Feed a complete, balanced diet, avoid raw meat and unpasteurized foods because of the infection risk, and keep the litter box clean. Keep a simple log of weight, appetite and energy so you notice slow changes.

Do not give human medicines, supplements marketed as immune boosters, or remedies you have read about online without your vet's approval. Some are toxic to cats and others interfere with treatment. If you have other cats, talk to your vet about testing them and separating bowls, litter boxes and bedding.

What the vet will likely check

FeLV is usually screened with a quick in-clinic blood test. Because results can be falsely positive or falsely negative, a positive is normally confirmed with a second type of test, such as IFA or PCR, and a cat with recent exposure may be retested after a few weeks or months. Cornell recommends retesting positive cats later to see whether the infection is progressive or regressive.

There is no treatment that removes the virus, so care focuses on keeping the cat well and treating problems early. Your vet may recommend checkups every six months, blood work to watch for anemia, prompt treatment of infections, and specific care for cancers such as lymphoma. Cornell reports a median survival of about two and a half years after diagnosis, with many cats living longer, especially those with regressive infections.

Prevention

Test every new cat before it meets your others, and keep cats indoors or in a secure enclosure so they cannot fight with or groom cats of unknown status. If one cat in the home is positive, the others should be tested and, where possible, kept separate.

Vaccination helps. VCA recommends the FeLV vaccine for all kittens, which are highly susceptible, and for any adult cat that goes outside, given as an initial course of two injections followed by boosters, after the cat has tested negative. No vaccine is fully protective, so it works best alongside limiting contact with unknown cats. Your vet can advise how often your cat needs boosters based on its lifestyle.

This page is general information, not veterinary advice, and it cannot replace an examination by the vet who knows your pet.