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Feline Leukaemia Virus (FeLV)

Cat disease FeLV

What is FeLV?

Feline leukemia virus (FeLV) is a virus that infects members of the cat family, not only in domestic cats, but also in wild cats, lynxes, jaguar and etc. However, it does not pose a risk to other species of animals or people.

FeLV was first discovered in cats with a form of leukemia (cancer of the white blood cells). It can cause a variety of diseases in addition to leukemia. Like all viruses, FeLV is a tiny microorganism that can only replicate itself inside living cells.

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 is FeLV transmitted?

Direct contact between cats is the most frequent method of FeLV infection, therefore, virus transmission is common in situations where there is a high population density of cats living socially together.

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 feces containing the virus. It is also possible for virus to be passed from a mother to her kittens either in the womb or after the kitten is born, via infected breast milk.

Luckily, the virus is fragile and cannot survive longer than a few hours outside of the cat. It can be killed effectively by general cleaner, disinfectants, soap, or heat and dry environment, so the owner could pay more attention on daily necessities cleaning to avoid the potential transmission from infected cat.

What are the clinical signs?

A wide variety of clinical signs can be observed in persistently infected FeLV infected cats, because the virus can affect in the immune system and cause other diseases. 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. 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.

In addition, cats infected with FeLV may develops Cancer. 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.

Outcomes of FeLV infection?

Basically, all cats are likely to be infected, and the more obvious symptoms develops with a younger infected cat as their incompletely developing immune system.

There is about 20 to 30% of cats with the capability to defeat the virus by their immune system, which is called abortive infection. Some cats that could fight off partial virus, but it’s not comprehensive, which is called regressive infection. The virus only reproduces in the blood for a short period of time, but there is a chance that it will break out again when the cat is getting weak.

And there are also some cats that continue to have the virus in their blood, which is called progressive infection that often leads to obvious symptoms of feline leukemia.

Is there any vaccine available?


Fortunately, vaccination is available which helps in preventing infection with FeLV and therefore in controlling FeLV-related disease. If you have multiple cats and found out one of the cats is infected, vaccine would be an option of protection, but remember all cats should be tested for FeLV prior to vaccination, because vaccine does not work on infected cat.

If possible, please quarantine infected cat, and do not allow healthy cats, particularly kittens, to come into close contact with known FeLV-infected cats or cats without a known history of proper vaccinations.

As with other vaccines, an initial course of two injections is required, and regular boosters are necessary to maintain immunity. So when’s the best time for cats to be vaccinated? It’s better to have first vaccination in kitten stage and in the initial vaccination series, two doses of vaccines administered one month apart are necessary to provide strong, lasting immunity. Even so, this immunity will decline over time and periodic revaccination will be necessary. Due to different situation of every cat, your veterinarian will discuss with you the most appropriate vaccination schedule for your cat.

Although vaccination could help in preventing infection with FeLV and therefore controlling FeLV-related disease, no vaccine is 100% protective. As the immune system of a cat with the virus is suppressed, it is important for FeLV positive cats to have regular veterinary checkup.

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. The treatment depends on the clinical signs and other health problem of the infected cat and your vet will provide the most appropriate medical plan.

If you have any further queries about FeLV. Please contact us for more advice.

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