Feline leukaemia virus (FeLV) is a significant viral infection of cats worldwide.

FeLV belongs to a group of viruses known as ‘oncornaviruses’ and these viruses can cause the development of tumours (cancer) in infected individuals. Cats infected with FeLV can develop lymphoma (a solid tumour of lymphocytes – a type of white blood cell), and leukaemia (cancer of the bone marrow). However, other major effects of FeLV infection are severe immunosuppression and the development of anaemia (pale gums and eyes), and more cats will die of these complications than from the development of tumours.

Infection is spread most commonly through prolonged social contact (mutual grooming, sharing of food bowls, litter trays etc., where virus may be ingested). However, the virus can also be transmitted through biting and kittens can catch the virus in the womb before they are born if their mother is infected.

FeLV is commonly found in young, unvaccinated sick/outdoor cats.

The best way to protect cats from FeLV is to vaccinate against it.

See our full guide to cat vaccination




Written by Dr. Mariella Roberts, Veterinary Surgeon, Animal Trust Vets CIC | Published January 2025 | Review date January 2027 | This advice is for UK pets only and is not a replacement for seeing a vet