Feline Leukaemia Virus (FeLV)


  • Feline Leukaemia Virus (FeLV) is a serious disease that affects cats.
  • It damages the immune system, increasing the risk of other illnesses and can cause cancers such as lymphoma and leukaemia.
  • FeLV spreads in bodily fluids such as saliva, snot, pee and poo.
  • Young, unvaccinated, un-neutered, outdoor cats living around lots of other cats are most at risk of catching FeLV.
  • Approximately 1 in 3 cats that come into contact with the FeLV virus develop a permanent infection which is almost always fatal.
  • The best way to protect your cat from FeLV is by vaccinating them against it.

What is FeLV?

Feline Leukaemia Virus (FeLV) causes serious illness in cats. Once a cat is infected with FeLV, the virus can cause a range of health problems such as:

A weak immune system:

FeLV weakens the immune system by attacking the bone marrow (bone marrow produces infection fighting cells). This makes it difficult for infected cats to fight off even common illnesses.


FeLV can lead to cancers such as lymphoma and leukaemia.

Anaemia, skin problems and reproductive issues:

FeLV can cause a range of other health problems such as:

  • Anaemia (a reduced number of red blood cells)
  • Skin problems
  • Reproductive problems such as pregnancy loss and infertility

How do cats catch FeLV?

FeLV is found in saliva, blood, urine, faeces, milk, and nasal discharge (snot). It spreads amongst cats that are in regular, close contact, for example:

  • Mutual grooming
  • Sharing food and water bowls
  • Sharing a litter tray (contact with urine and faeces)
  • Sexual contact
  • Biting
  • Kittens can catch FeLV in the womb before they are born, or from their mother’s milk after they are born.

FeLV is most common in young, unvaccinated, un-neutered, outdoor cats because they tend to roam, fight, and have sexual contact with other cats.


FeLV can present itself in many ways, and cause a range of vague symptoms such as:

Please note that many of the symptoms listed above are common and can indicate many conditions other than FeLV.


FeLV can be detected on a blood test. Your vet may also suggest repeating the blood test after a few weeks to confirm their diagnosis. 

If at any point, your cat tests positive for FeLV, they will need to be isolated from all other cats while their diagnosis is confirmed.


Sadly, there is no cure for FeLV, so the only treatments available are supportive therapies to keep your cat as happy and healthy as possible for as long as possible. This will include:

Staying indoors

Cats with FeLV must be kept indoors to prevent them spreading FeLV to other cats, and to prevent them from catching any other illness that they will struggle to fight due to having a weakened immune system. If your cat has always been free roaming, it’s important to consider how this might affect their quality of life. If your cat is finding an indoor lifestyle very stressful, speak to your vet about what is best for them, sadly, in some cases, it’s so stressful for the cat to be kept permanently indoors it may be kinder to put them to sleep.

Prompt vet care

If a cat with FeLV becomes unwell, it's important to get them to the vet quickly because their immune system will struggle to fight infections on its own.

Preventative health care

It’s important that FeLV positive cats stay up-to-date with vaccines, flea and worming treatment. They will also need a vet health check every 6-12 months (or more often if necessary).

Good nutrition

Cats with FeLV should be provided with good quality, complete cat food. They should never be fed raw meat because their weak immune system may struggle to fight any harmful germs within it.

Live as a single cat

Cats with FeLV shouldn’t live with other cats unless they are also FeLV positive. Fortunately, many cats prefer living without other cats, so this is isn’t often a problem.


Approximately one in three cats that come into contact with the virus develop a permanent infection which is almost always fatal. Sadly, many cats that become poorly with Feline Leukaemia Virus, need to be put to sleep within three years of their diagnosis to prevent suffering.


The best way to protect your cat from FeLV is through vaccination. Your cat’s first vaccines should be at 9 and 12 weeks of age, then they will need regular boosters throughout life.

When to contact your vet

Always speak to your vet if you are concerned your cat might have FeLV.

If your cat has been previously diagnosed with FeLV and seems unwell, have them checked ASAP.

You know your cat best.  Even if they don’t have the symptoms listed above, if you’re concerned it’s always best to contact your vet.


Treatment for a poorly cat with FeLV can become very expensive. Consider insuring your cat as soon as you get them, before any signs of illness start. This will ensure you have all the support you need to care for them. It’s also very important to speak openly to your vet about your finances, the cost of treatment, as well as what you think is right for your cat. There are often several treatment options so if one doesn’t work for you and your pet then your vet may be able to offer another.


Can people or dogs get FeLV?

No, only cats can catch and suffer from FeLV.

Are FIV and FeLV the same thing?

No, although FeLV (Feline Leukaemia Virus) and FIV (Feline Immunodeficiency Virus) both weaken the immune system and cause similar symptoms, they are different diseases caused by different viruses.

How can I safely bring a new cat into my household?

Before introducing a new cat to your home, it’s a good idea to have them vet checked and vaccinated for FeLV. Depending on their history and health status, your vet may also recommend testing for FeLV before vaccinating them.

Published: December 2023

Written by vets and vet nurses. This advice is for UK pets only. Illustrations by Samantha Elmhurst.