What is Feline Leukaemia?
Understanding Feline Leukaemia Virus (FeLV)
Feline Leukaemia Virus (FeLV) is a serious viral infection in cats that can lead to tumour formation, anaemia, and immune system suppression. When the immune system is weakened, affected cats become more vulnerable to other illnesses and infections, which can often be more severe and harder to fight off. This condition is somewhat comparable to AIDS in humans and Feline Immunodeficiency Virus (FIV) in cats.
Which Cats Are at Risk of FeLV?
FeLV does not survive long in the environment, meaning infection typically spreads through close and prolonged contact between cats. It is most common in multi-cat households, outdoor cats that socialise or fight, and environments such as catteries, rescues, or feral colonies.
Current estimates suggest that around 1–2% of cats in the UK carry the FeLV virus, though infection rates can reach up to 30% in groups where the virus is endemic.
Kittens and young cats are especially vulnerable, as their immune systems are not yet fully developed. While older cats tend to be more resistant, vaccination is still advised for those considered at risk.
How Is Feline Leukaemia Virus Spread?
The main route of FeLV transmission is through saliva, often passed via mutual grooming, shared food and water bowls, or biting during fights. The virus can also spread through urine and faeces.
Mother cats can pass the virus to their kittens during pregnancy (through the placenta) or after birth via infected milk.
Once inside the body, FeLV replicates in the mouth or nasal tissues before entering the bloodstream and spreading to organs such as the bone marrow. If the cat’s immune system cannot eliminate the virus within 4–12 weeks, a persistent infection develops, meaning the cat will carry the virus for life.
Signs and Symptoms of FeLV
Cats infected with FeLV may not show signs for months or even years. Early symptoms are often vague and non-specific, but may include:
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Reduced appetite and gradual weight loss
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Persistent or recurrent infections
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Lethargy or weakness
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Poor coat condition
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Diarrhoea or vomiting
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Slow recovery from minor illnesses
In more advanced cases, affected cats may develop tumours in areas such as the chest, kidneys, digestive system, or spinal cord. As the bone marrow becomes damaged, anaemia develops — leading to pale gums, fatigue, and listlessness due to reduced oxygen levels in the body.
Treatment for Feline Leukaemia Virus
Currently, there is no cure for FeLV. Treatment focuses on supportive care to maintain your cat’s comfort and quality of life. This may include:
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Managing secondary infections and anaemia
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Controlling symptoms related to cancer
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Nutritional support and stress reduction
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The use of interferon therapy in certain cases to help modulate the immune response
With careful veterinary management, some cats can live comfortably for a considerable time after diagnosis.
Preventing FeLV in Cats
The best way to protect your cat from FeLV is through vaccination. Several effective FeLV vaccines are available, designed to prevent persistent infection by stimulating a strong immune response.
While no vaccine is 100% protective, vaccination is strongly recommended for:
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Cats that go outdoors
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Cats living with or near other cats
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Cats in multi-cat households or rescue environments
Keeping your cat indoors, avoiding contact with unknown cats, and regular veterinary check-ups can further reduce the risk of exposure.
Summary
Feline Leukaemia Virus remains one of the most serious infectious diseases in cats, but through awareness, testing, vaccination, and responsible care, it is possible to protect your pet and maintain their wellbeing for years to come.