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What is Feline Leukaemia virus?

Feline leukaemia virus (FeLV) is an important retroviral infection that can occur in cats. It is a member of the same virus family as feline immunodeficiency virus (FIV).

The most common effect of FeLV infection is immunosuppression. The virus infects the cells of the cat’s immune system by killing or damaging them. This leaves the cat vulnerable to a wide variety of other diseases and secondary infections. Cats that are persistently infected with FeLV have an increased risk of developing cancers such as lymphoma and leukaemia, as well as severe anaemia.

How can my cat catch the virus?

The major source of virus is in the saliva from a persistently infected cat. Virus is spread by activities where saliva is exchanged between cats, such as mutual grooming or sharing of food bowls. Alternatively, FeLV infection of other cats may be caused by biting or contact with urine and faeces containing the virus. It is also possible for virus to be passed from a queen to her kittens either in the womb or after the kitten is born, via infected milk. However, it is uncommon for FeLV-infected cats to give birth as FeLV usually causes pre-natal death of the kittens.

Not all cats which are exposed to FeLV become persistently infected. Either they have not been exposed to enough virus or their body’s immune system is successful in eliminating the infection. The majority of cats become infected with the virus entering the body via the mouth or nose. The virus multiplies at these sites before spreading, in the bloodstream, to the rest of the body and in particular to the bone marrow. If the cat is able to eliminate the virus, this will occur during the initial stages (4 – 12 weeks) of infection. Once significant infection of the bone marrow is present, the cat remains infected for the rest of its life.

Very rarely FeLV infection may be limited to certain parts of the body such as the mammary (breast) tissue or bone marrow. This is known as a ‘localised infection’. These infections may be difficult to diagnose as there is no virus in the bloodstream for the test detect.

Is my cat at risk from the virus?

FeLV is a fragile virus which is not able to survive for long in the environment so spread of infection between cats relies on prolonged and close social contact. For this reason infection is most common in situations where there is a high population density of cats living socially together. The Eastern coast of Australia is fortunate to have very low FeLV infection rates with studies showing a prevalence of about <2% of the cat population. Sadly the cats of Perth have a significantly higher prevalence of FeLV at around 7-11%.

Young cats, particularly those less than six months old, are especially vulnerable to becoming persistently infected.

What are the symptoms?

A wide variety of clinical signs can be observed in persistently infected FeLV infected cats however the majority often show a degree of weight loss, lethargy and general poor health. These symptoms tend to progressively deteriorate as time progresses.

More specific clinical signs are extremely diverse but can include fever, lethargy, poor appetite and weight loss. Anaemia is very common and quite often severe and can be seen in up to 25% of cases. Anaemic cats show clinical signs such as weakness, lethargy and increased breathing rate. Respiratory, skin and intestinal signs are also common. Cats may suffer from several illnesses at the same time.

Cancer develops in around 15% of cats infected with FeLV. The most common is lymphoma, a cancer of lymphocytes (a type of white blood cell) resulting in solid tumours or leukaemia (tumour cells in the blood stream). Solid tumours can be seen at various sites including the intestine, kidneys, eyes or nasal chambers. In multi-centric lymphoma, the tumour involves multiple lymph nodes and other sites.

What treatments are available for the disease?

There is currently no known cure for FeLV and therefore treatment is targeted at maintaining a quality of life and treating the secondary diseases that arise as a result of the viral infection. Because the immune system of a cat with FeLV is suppressed it is important that as soon as he or she shows signs of any illness that they are seen promptly by a veterinarian. FeLV positive cats should receive regular quarterly veterinary health checks. A minimum of twice yearly blood testing is also advised.

Premium diets are recommended to ensure optimum nutrition for your cat and it is recommended to avoid feeding them any raw meat as their suppressed immune system makes them at an increased risk of developing infections. It is vital to maintain excellent preventative health care including regular worming, vaccination and flea control.

It is recommended that you house your FeLV positive cat strictly indoors only in order to prevent them contracting any diseases from other cats, but also to prevent your cat spreading FeLV virus to your neighbour’s cats.

Anti-viral medications: There are a number of anti-viral medications used to treat humans with HIV. There have been some reports of successful use in FeLV cats, although there is a risk of some severe side effects including bone marrow suppression. These drugs are fairly costly to use long term. Your vet can help determine whether anti-viral drugs are suitable for your cat.

Is there a vaccine available?

A vaccine for FeLV is available. Vaccination is recommended in situations where cats have a high risk of exposure to the virus. This includes any cat that goes outdoors unsupervised, or that mixes with a cat that goes outdoors unsupervised, or that mixes with a cat of unknown FeLV status (such as a rescued stray). The aim of the vaccine is to prevent cats exposed to the virus from becoming persistently infected. All of the vaccines aim to do this by stimulating a successful immune response to FeLV. Unfortunately, no vaccine is likely to be 100% effective at protecting against infection.

Kittens need two injections that can be given at the same time as normal kitten vaccination course.  Adult cats also need two injections initially but usually require blood testing first to make sure they haven’t already got the disease. After this, annual boosters are recommended for cats that remain at risk of infection.

It is important to remember that a fully vaccinated cat may still not be fully protected from FeLV infection. Therefore it is not recommended to knowingly to mix an FeLV-infected cat or a cat of unknown FeLV status with a vaccinated uninfected cat. All new cats to your household should be tested for FeLV (And FIV) prior to introduction to your other cats. Unlike FIV vaccines, the FeLV Vaccination does not interfere with the FeLV blood tests.

Please don’t hesitate to call us at Perth Cat Hospital for more advice if you have any further queries.

Disclaimer: Please note that the information provided on this page does not replace the advice of your veterinarian. If you are concerned about your cat’s health in any way, we strongly recommend you seek veterinary advice. 

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