

What is Feline Leukaemia Virus
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 | This advice is for UK pets only

Symptoms of FeLV
Immunosuppression is the single biggest cause of clinical signs in FeLV-infected cats. Typically, a variety of symptoms develop in these cats, with progressive deterioration in their condition over time. Clinical signs are extremely diverse but include fever, lethargy, eating little, weight loss, persistent or recurrent breathing issues, skin and gut problems such as vomiting or diarrhoea, and anaemia (pale gums and eyes).
When to contact your vet
If your cat has any of the symptoms above or if you are concerned your cat may have FeLV or was previously diagnosed with FeLV and now seems unwell.
Diagnosis of Feline Leukaemia Virus
Blood tests are used for diagnosis. Re-testing is sometimes required after 12-16 weeks to confirm the status of a cat. If the cat has only recently been exposed, it may test negative for the virus. Any cat that tests positive for FeLV should be isolated from other cats to prevent it spreading to others.
Treatment of FeLV
There is no cure for FeLV infection, and management is largely aimed at symptomatic and supportive therapy. This includes: prompt diagnosis and treatment of secondary infections; maintaining good quality nutritional support and avoiding raw foods that may put the immune system under greater pressure from germs; maintaining a good preventive healthcare programme with routine veterinary visits at least twice a year and regular worming, flea treatments and vaccination; keeping infected cats indoors to prevent the spread of infection to other cats and to reduce the exposure to other infectious agents; in some cases, supportive therapy may include use of blood transfusions and drugs to manage anaemia. | Although no treatments can cure FeLV infection, some drugs may help to reduce viral replication and improve the condition of infected cats.
Prevention of Feline Leukaemia Virus
FeLV vaccination has been proven to be successful. Several vaccines are available, and these generally appear to provide a valuable level of protection against infection.
Outlook
FeLV–related disease is usually fatal with 80%-90% of FeLV-infected cats dying within three to four years of initial diagnosis. This is why vaccination programs are so important to reduce the disease.
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