Feline leukaemia virus (FeLV) is a virus that affects cats. It can weaken the immune system, cause anaemia and lead to certain cancers.
FeLV spreads mainly through contact with an infected cat’s saliva, for example during mutual grooming, sharing food and water bowls, or through bites. An infected mother can also pass the virus to her kittens during pregnancy or through her milk.
Not every exposed cat develops a lasting infection. Some clear the virus or keep it under control, while others remain infected and may develop serious illness. Kittens, cats with weakened immune systems and those repeatedly exposed to the virus are at greater risk of persistent infection. Infected cats may appear healthy for months or years.
Vaccination and avoiding contact with infected cats help reduce the risk. FeLV does not infect people.
Cats with FeLV may initially show no signs of illness. When symptoms develop, they vary depending on how the infection affects the cat.
Signs may include:
Weight loss or reduced appetite
Unusual tiredness or weakness
Persistent or recurring infections
Poor coat condition
Pale gums, which may indicate anaemia
These signs can have many other causes and do not confirm FeLV infection.
Contact your vet if your cat has unexplained weight loss, reduced appetite, persistent illness or recurring infections, or if you think they have been exposed to FeLV.
If your cat has already been diagnosed with FeLV, seek advice promptly whenever they become unwell.
Difficulty breathing, collapse or severe weakness requires emergency veterinary care.
FeLV is diagnosed using blood tests. An initial screening test may need confirmation with further laboratory testing.
A negative result soon after exposure may be too early to detect infection. A positive result does not always establish whether infection will persist, so repeat testing may be needed. Your vet will advise on the timing and explain what the results mean.
While a positive result is being investigated, keep your cat separate from FeLV-negative or untested cats to reduce the risk of transmission.
There is no treatment that reliably eliminates FeLV. Care focuses on maintaining quality of life and treating any illnesses that develop. Cats that appear well may not need medication, but regular veterinary checks are important.
Infections and other complications should be investigated and treated promptly. Treatment depends on the problem and may include antibiotics for bacterial infections or treatment for anaemia or cancer.
Feed a balanced, complete diet and avoid raw meat because of the risk of infection. Your vet will advise on vaccinations, parasite prevention and monitoring.
Keep your cat indoors, with appropriate space, enrichment and opportunities to play. This helps protect them from other infections and prevents contact with cats that could catch FeLV.
Vaccination is an effective way to protect cats against FeLV. Your vet will advise on the initial course and boosters according to your cat’s age and lifestyle.
Before introducing a new cat to your household, discuss FeLV testing with your vet, particularly if their history or infection status is unknown.
Cats with FeLV should be kept indoors and separate from FeLV-negative cats to prevent the virus spreading.
The outlook depends on whether a cat controls the infection or develops progressive infection, and whether FeLV-related illness is present.
Cats with progressive infection have a reduced life expectancy, although some remain well for several years. Serious complications, including anaemia, recurrent infections and cancer, can be fatal.
Your vet will interpret the test results alongside your cat’s health and discuss their likely outlook. If illness can no longer be managed while maintaining a reasonable quality of life, euthanasia may need to be considered.
Written by Gillian Burkhill, Veterinary Surgeon, Animal Trust Vets CIC | Published November 2026 | Review date November 2029 | This advice is for UK pets only and is not a replacement for seeing a vet
