Feline Leukemia Virus

Picture of a grey cat outside

Feline Leukemia Virus is one of the most common diseases in cats; it affects around two to three percent of all cats in the U.S. The percentage is much higher in cats that are at risk or suffering from an illness. In the past quarter-century, the prevalence of this infectious disease has decreased considerably, especially since the vaccine was developed, along with various testing procedures.

Let’s Look at the Clinical Signs, Diagnosis, Treatment, and Prevention of Feline Leukemia

How is feline leukemia spread?

Cats that are infected with FeLV are carriers, so they represent sources of infection for other cats. The virus is shed in nasal secretions, urine, saliva, feces, as well as the milk of queens. From one cat to the other, the transmission can occur either through a bite, through mutual grooming, but also through the shared use of feeding dishes or litter boxes.

Viruses (including this one) don’t usually last in the environment for a long time, and that’s why indirect transmission is less likely. FeLV survives less than a few hours in regular conditions.

An infected mother can also transmit the virus to her kittens, either before giving birth to them or while they are nursing.

Outdoor cats are at a greater risk than those that live indoors, especially those that live with cats that were vaccinated against the disease. You can’t really know whether your pet will come in contact with a carrier if the cat goes outdoors unsupervised.

Kittens are more susceptible to getting the disease compared to adults and have a greater risk of developing the infection. Feline leukemia life expectancy in this age category is extremely low, and kittens that have gotten it from their mothers rarely survive.

Signs of Feline Leukemia

There are many feline leukemia symptoms, and part of the reason they can be so diverse and can vary from one cat to the other is that their immune system can be healthier or not. The disease is, however, one of the most common causes of cancer in domesticated felines and can produce a state of general immune deficiency.

This makes it very hard (if not impossible) for the cat to protect herself against infections that would normally not affect her at all. Usually, the secondary infections are the culprits for the many medical conditions that are associated with feline leukemia.

Adult cats can show no clinical signs at all in the early stages of infection. However, as time goes by and the cat’s health deteriorates, the animal could experience repeated cycles of illness. Some of the symptoms that pet parents will notice are a loss of appetite, poor coat condition, persistent fever, progressive weight loss, an increase in the size of the cat’s lymph nodes, and pale gums. Mouth and gum infections and inflammations could also be present, as well as skin and urinary infections. Additionally, clinical signs such as persistent diarrhea, seizures, eye conditions or the abortion of kittens can also be noticed.


It used to be extremely complicated to find out whether one cat had feline leukemia or not. Fortunately, that became a lot simpler with the introduction of feline leukemia tests. There are two types of blood tests commonly utilized to diagnose the disease, and both of them detect a protein component of the virus.

The cost of a test at the vet can range from $70 to $100 depending on the vet and the clinic you go to. If the result of the first test is positive, a second one should be performed so as to eliminate any doubt that the cat is not suffering from feline leukemia. You can also get quick tests from Amazon for around $50 (which you can do at home).

Treatment and Prevention

At this point in time, no definitive feline leukemia treatment exists. Vets can treat and manage FeLV-positive cats that show any signs of disease by prescribing antibiotics and any medication that combats secondary infections. If the cat has anemia, she can also get blood transfusions.

One of the most effective ways of preventing the disease is by avoiding the cat’s exposure to the outdoor environment, particularly in the case of cats that have not been vaccinated against FeLV. Outdoor access is allowed with supervision, which means that you can take your cat outside in a leash and harness. If you have other cats, it’s a good idea to avoid introducing a new one into the living environment of the other ones before having her tested.

It’s often that cats that are infected with FeLV don’t show any symptoms in the initial stages of the disease, which is why they might end up being tested much later. Therefore, they could transmit the virus to other cats with which they share their living space. If one cat from a colony is diagnosed as positive for FeLV, all of the others need to be tested.

There is a vaccine available against this infectious disease, but it does not protect 100% of cats that were vaccinated. Although vaccination is highly recommended for cats that spend a lot of their time outdoors, you may have to speak with your veterinarian to find out whether it makes sense for you and your feline friend, especially if he or she lives only indoors.

Feline Leukemia Vaccine Side Effects

All vaccines have a number of side effects, no matter what medical conditions they are used against. Some of the common symptoms that you might notice in your cat after she was vaccinated are lethargy, fever, pain or swelling at the injection site. In some cases, a granuloma or a vaccine associated sarcoma could show up at the injection site.

The vaccine has been improved over the years, and nowadays, modern ones rarely contain adjuvants that could cause such issues. Although the vaccine does have side effects, many cats are at a greater risk of contracting the virus than they are of developing any of these adverse reactions. It’s important to underline that there is no cure for FeLV at this time, so vaccination is pretty much the only way of preventing the disease.

The bottom line

Is feline leukemia contagious? Yes, very much so. The disease can pass from one cat to the other through mutual grooming and bites, and it can also be transmitted from the mother to the fetuses and kittens either before the birth or while they are nursing.

There is no cure for this disease, and that is why vaccination is highly recommended, especially for cats that spend most of their time outdoors. The vaccine does have a series of side effects, but considering the prognosis of the disease and the fact that it is the only prevention method that exists, it might be the only choice.

Kittens that have feline leukemia rarely survive and cats that were infected can show no symptoms for a period of time. The virus affects their immune system to the extent that any ordinary infection can cause severe illness.



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