One of the most dangerous diseases in cats: what do you need to know about feline leukosis?

László Enikő

2022. February 15 - Photos: Suttogó Veterinary Clinic, Getty Images Hungary

Feline leukaemia, often referred to as FeLV in the common parlance, is an incurable, sometimes fatal disease. But vaccination could prevent the problem.


All cat owners are probably familiar with the disease Feline Leukaemia Virus (FeLV). According to the statistics in Hungary, 8-9% of owned cats are affected, but this figure can be three times higher in stray cats. 85% of the infected cats die within three years of diagnosis. It is no coincidence that feline leukosis is one of the nightmares of cat owners. It is the second leading cause of death for cats, followed only by accidents. But with the right attention, the problem could be prevented.

What is feline leukosis?

Feline leukosis is an incurable disease that significantly weakens the immune system and can cause anaemia. Individuals infected with the virus often appear perfectly healthy, making it easy for them to pass on the deadly disease to others. The biggest threat is from stray cats, which often spread the virus. The disease only affects cats, so it poses no threat to humans or other animals.

How is the disease spread?

FeLV is typically transmitted from one individual to another through nasal secretions or saliva. It is most commonly spread by grooming, licking, fighting and biting. However, kittens can be infected either in utero or through contaminated breast milk.

Kittens can also get the disease from breast milk.

Clearly, the most at risk are cats that are loose or stray, and those with weak immune systems. Often unneutered male cats spread the virus. Because FeLV is highly contagious, cats living in the same household can easily pass it on to each other. The sick animal must be completely separated from the others.


The symptoms can be very diverse. They can depend on the age of the animal, the state of its immune system and the amount of virus. In the beginning, lethargy, fever, loss of appetite may be signs. In advanced stages, the virus can damage bone marrow, which can lead to anaemia. The animal’s mucous membranes become pale, its lymph nodes can become enlarged and even develop tumours. The virus can even cause eye diseases or nervous system problems. Secondary infections can also attack the cat because of a weakened immune system.

Photo by Suttogó Veterinary Clinic

How is the diagnosis made?

If you are experiencing any of the above symptoms in your cat, you should take him to the vet as soon as possible. Rapid tests can be used to determine whether feline leukosis is behind the problems. However, these tests are not always completely reliable, because if there is no virus circulating in the bloodstream of the infected animal, the result will be negative. Therefore, in case of doubt, it is worth repeating the test after 4-8 weeks.

If your cat has feline leukosis

FeLV is an incurable disease, there is no way to eradicate the virus from the cat’s body, so in the vast majority of cases the animal remains infected and thus infectious for the rest of its life. The vet recommends that such cats should be kept separate from others. In addition, it is important to take immune-boosting medicines and to have annual and biannual check-ups.

Photo by Suttogó Veterinary Clinic

How can the disease be prevented?

First and foremost, it’s important not to let your pet roam free. Neutering helps with this problem, as it means that the cats are less likely to run off and fight. Another very important step is to vaccinate your pet. Before administering the vaccine, the vet will make sure that the cat is not yet infected with the virus. If it is healthy, it can have the vaccination, which then needs to be repeated every year. However, despite the vaccination, it is still very important that you do not let your cat roam the streets.

Dr. Regina Matuska, the Suttogó Veterinary Clinic veterinarian said this about feline leukosis:

“Feline leukosis is one of the most common, incurable viral diseases of cats. 95% of infected cats remain infected for life, and can infect other cats. Such cats should be kept alone or with other FeLV positive cats. It is said that “cats pass leucosis on to their friends”, as they can even contract the virus from grooming each other. As with all viral diseases, it is mainly outdoor cats that are at risk. Among these, unneutered, stray, frequently fighting cats are the most at risk of the disease.

The course of the infection depends on the kitten’s immune system. Immunosuppressed individuals may die after a few weeks from complications of the infection. But a cat with a stronger immune system can live for years without symptoms. However, it is important to point out that it can still be infected and therefore cannot meet other cats.

Rapid tests can detect the viral antigen in a few drops of blood, but these are not 100% reliable, so if there is a strong suspicion, the test may need to be repeated a few weeks later. Unfortunately, according to our current knowledge, the disease is incurable, we can only treat the symptoms.

Vaccines are available to prevent the virus, and it is important to keep animals indoors, spay and neuter them, and avoid colonies of cats with uncertain immune status.”

cat diseases disease symptoms feline leukosis FeLV Health vaccination

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