Feline leukaemia virus (FeLV) is a viral infection of cats occurring worldwide which can cause lymphoma, leukemia and tumours, as well as other side effects such as immunosuppression and anemia.

A cat persistently infected with FeLV is highly likely to develop clinical disease related to the virus. However, the development of effective vaccines and readily accessible tests have significantly reduced the prevalence of this disease.

Causes of FeLV

Feline leukaemia virus (FeLV) belongs to a group of viruses known as oncornaviruses – a group of viruses which can affect humans and animals. FeLV only causes disease in cats, and was first discovered in 1964.

In cats that are permanently or consistently infected with the virus, there is significant risk of severe illnesses from anemia, immunosuppression and cancer.

It is thought that infection is spread most commonly through prolonged social contact with other infected cats (sharing food, litter trays, grooming etc). It can also be transmitted through fighting or passed to kittens from an infected mother.

FeLV is not common in healthy cats and is most prevalent in sick or outdoor felines.

Symptoms of FeLV

Clinical signs of FeLV are extremely diverse and are most typically a variety of chronic and/or recurrent issues, which get progressively worse over time:

  • Fever
  • Lethargy
  • Poor appetite
  • Weight loss
  • Anemia
  • Persistent issues with respiratory system, skin or intestinal problems

An increase in recurring symptoms such as those above suggest a progressive deterioration of the cats immune response and ability to deal with infections.


Fortunately, reliable tests for FeLV exist. Most vets will test for FeLV and FIV at the same time, and the tests are quick, readily available and affordable. Re-testing is sometimes required to confirm the status of a cat or to rule out false negatives – especially if it is an outdoor or colony cat. Any cat that tests positive for FeLV should be isolated from other cats to prevent transmission.

Treatment & management

There is no cure for FeLV infection, and it is usually managed with supportive therapy including treatment of secondary infections, high quality nutrition, regular parasite treatment and vaccinations. In some cases, therapy may include various medications or Chemotherapy.

Although no treatments can cure FeLV infection, some antiviral drugs may help to reduce viral replication and improve the condition of infected cats.


To prevent cats being exposed to FeLV, the following measures should be carried out:

  • The FeLV and FIV status of any cat should be known when possible.
  • Any FeLV positive cat should be kept apart from other cats and kept indoors to prevent spread of infection to other cats
  • The FeLV vaccination has been proven to be successful and should be considered

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