FeLV – Feline Leukaemia Virus – Symptoms, Treatment and Prevention.

FeLV, an acronym that will be familiar to those that are actively involved in cat rescue and adoption. Feline Leukaemia Virus, also known as FeLV, is a relatively common infectious disease in cats. Due to its common nature, it’s one of the diseases cats often get tested for, if they are rescued by adoption centers or rescue organisations, together with other diseases such as FIP and FIV. Knowing some basic information about FeLV as a cat owner is useful, so symptoms can be recognized, and infections prevented.


Feline Leukaemia Virus is an infectious disease that is seen worldwide in around 1-2% of the cat population. Kittens are most susceptible to a FeLV infection when exposed, but even healthy adult cats can contract this disease.The infection is shed in nasal secretions, urine, saliva, faeces, and milk, making FeLV more common in colonies of cats where there is close contact between one another. House cats are mostly at risk when they spend prolonged periods of time with an infected cat, or those that are allowed to go outdoors unsupervised. 

While the main source of transmission of FeLV is through bite wounds, in cases where there is prolonged contact with bodily secretions, the virus can also be transmitted through mutual grooming, through shared litter boxes and food dishes. FeLV can also be transmitted by infected mother cats in utero to her kittens, and through her milk while nursing. 

Regressive and Progressive FeLV Infection

Not all cats that get infected with FeLV will develop a persistent infection. In about 20-30% of the cases, cats can eliminate the virus before it spreads through their body. 

In 30-40% of the cats that get infected with FeLV, the infection will spread into bone marrow or organs, before the immune system removes it from the bloodstream. This state of the disease is referred to as a regressive FeLV infection. Cats with a regressive FeLV infection often aren’t contagious to other cats until the infection starts circulating in the bloodstream again, which often happens when their immune system is suppressed and/or they are stressed. At this point they become contagious again and can develop FeLV related diseases. 

The last 30-40% of the cats that get infected, will be unable to get rid of the infection before it spreads to lymph nodes and organs. This stage of the disease is also referred to as a progressive FeLV infection. Cats that have a progressive FeLV infection are permanently infected with the virus, are contagious, and are constantly at risk of developing FeLV-related diseases.


FeLV is a progressive disease. Most cats will show no symptoms in the early stages of the infection. As the disease progresses, the health of the cat will deteriorate overtime and they will often enter cycles of getting ill and feeling better. Once cats are infected with FeLV and start showing symptoms, these are usually diverse, and can include:

  • Weight Loss
  • Fever
  • Poor coat condition
  • Pale gums
  • Loss of Appetite
  • Gingivitis(inflammation of the gums
  • Inflammation of the mouth
  • Eye conditions
  • Diarrhoea
  • Skin Infections
  • Urinary infections
  • Upper respiratory tract infection
  • Seizures
  • Neurological symptoms
  • Behaviour changes.

FeLV affects cells of the cat’s blood forming tissues and immune system, which can lead to mutations in the cell’s genetic code, turning them potentially cancerous. Once the immune system is affected, cats will be more susceptible to secondary infections and will have more chances of getting seriously ill from common viruses, bacteria,fungi and, protozoa, that in normal situations would not affect a healthy cat. Life-threatening anaemia is also common in cats with FeLV. 


A FeLV infection can be diagnosed through a blood test. One of these tests is called the ELISA test, which can be done at the veterinary clinic. The ELISA test will detect if there are any FeLV particles in the bloodstream of the cat. The ELISA test is usually used as the first screening test to see if a cat is infected. When an ELISA test comes back positive, an additional  immunofluorescent antibody assay (IFA) can be done, which is sent to a diagnostic laboratory. This test will detect if the virus particles are detected within the white blood cells, which would indicate a more advanced infection. 


Treatment and Prognosis

There is no cure for FeLV, and treatment is mainly aimed at treating symptoms, such as giving antibiotics when a bacterial infection occurs, and blood transfusions when severely anaemic. There are therapies available which decrease the amount of FeLV in the bloodstream of infected cats, but they have significant side effects and the treatment is not in all cases effective.

Adult cats that have a progressive FeLV infection often live between 2 to 6 years after diagnosis. For kittens this is 6 months to 2 years. Cats with a regressive FeLV infection have a normal life expectancy according to research.


Under normal household conditions, FeLV can’t survive long on surfaces, probably less than a few hours. While bite wounds are the main way of transmission as they can readily transmit infection, passing of the infection can also happen through mutual grooming, and while more rare, also through sharing of litter boxes and food dishes. As infections happen through direct contact, the best way to prevent FeLV is to prevent contact with infected cats. Mother cats can pass on the infection in utero, and through their milk, however, infected female cats are often infertile or the kittens pass before being born.

There is a FeLV vaccine available, which is 85%-98% effective. The FeLV vaccine is not a core vaccine and owners can discuss with their veterinarian if a FeLV in their situation is suitable. Preventing exposure is still of importance after vaccination as the FeLV is not 100% effective and some cats will not be protected by the vaccine. FeLV vaccines do not cause false positives on FeLV blood tests. 

FeLV is an infection specific to the cat family and can’t be transmitted to people, or other species of animals. 


There is no cure for FeLV, so it’s best to prevent an infection from occurring. This mainly is done by not letting your cat get in contact with FeLV positive cats. When welcoming a new cat into the family, it’s advised to test them for FeLV before letting them mingle with the resident cats. 

If you would like to know more about our cat sitting and cat relocation services, feel free to contact us. Our team will be happy to help.

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