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The Complete Guide to Feline Leukemia Virus (FeLV)

Posted in: Cat Health - Last Updated: January 14, 2022 - Author: Rebekah Carter
Posted in Cat Health 
Last Updated: February 18, 2021  
Author:  Rebekah Carter

Feline Leukemia Virus, or FeLV, is one of the most worrisome conditions for any cat parent to face. The unfortunate reality is that FeLV is the second most common cause of death in cats, preceded only by trauma.

Feline Leukemia virus kills around 85% of cats with ongoing infections within 3 years of their diagnosis, often causing significant issues with lymphoma, anemia, and a damaged immune system. Crucially, exposure to FeLV won’t be a death sentence for every cat. Some kitties can mount an effective immune response on their own. However, as a pet owner, it’s up to you to ensure that you’re properly protecting your cat against any risks.

Here’s your guide to Feline Leukemia (FeLV) and everything you need to know about defending your furry friend.

What is Feline Leukemia Virus (FeLV)

Feline Leukemia virus is a dangerous virus that attacks a cat’s immune system and can prompt mutations that lead to cancerous growths. Cats with FeLV are more likely to develop other diseases and infections.

So, how common is Feline Leukemia (FeLV)? According to the College of Veterinary medicine for Cornell University, the condition affects up to 3% of all healthy cats in the US, and up to 30% of high-risk felines. This is an infectious and contagious viral disease that can be spread between cats through saliva and blood contact. In some cases, Feline Leukemia (FeLV) can also spread through feces, and urine.

FeLV is very susceptible to spreading through everything from licking and biting, to sneezing, and sharing food bowls with another cat. Kittens can even catch Feline Leukemia (FeLV) when in the womb, or by consuming their mother’s milk.

Feline Leukemia (FeLV) is most likely to affect unvaccinated, and unneutered cats who spend a lot of time outdoors. Though it’s possible to pass this disease through fighting, cats can even spread FeLV by rubbing noses or grooming each other.

While a portion of cats with this condition manage to fight it off, many are unable to do so. In rare cases, there are also kitties who carry the virus but appear healthy. These cats could become ill at any time and can spread the condition to others.

Which Cats are at Risk of Feline Leukemia (FeLV)?

Virtually any cat could be at risk of contracting feline leukemia, particularly as it’s possible to pass the disease from mother to kitten. However, your cat is likely to be far more at risk if it’s often allowed to venture outdoors or interact with other cats who have been outside.

Interestingly, older cats are less likely to contract the FeLV disease because their resistance and immune system seems to build up over time. For indoor-only cats who are otherwise healthy, the risk of contracting FeLV is low. However, it’s important to be cautious if you ever expose your cat to other felines, perhaps in a cattery setting.

The best thing you can do to protect your cat is keep them indoors, vaccinated, and protected from the outside world. If your cat is an outdoor cat or has a low immune system for some other reason, then your vet might be able to offer you some advice on how to protect them.


Most vets will recommend keeping any high-risk or unwell cats indoors so you can avoid exposing them to other dangerous infections and ailments that they might encounter outside. However, if you have a particularly at-risk cat, there’s also a chance that your vet will offer you a recommendation for a vaccination. The vaccination should only be given to a cat that tests negative for feline leukemia but is still identified as high risk.

Notably, while this vaccine might help to protect your cat, there’s no guarantee that it will stop them from getting sick completely. Your vet will still ask you to arrange regular checkups where your cat can receive tests that will diagnose any conditions.

What are the Symptoms of Feline Leukemia (FeLV)?

Feline Leukemia (FeLV) infections are complicated.

After exposure to the virus, your cat will go through a period where the virus may attack various systems within their body. Interestingly, the signs and symptoms of the condition can differ depending on which of the cat’s systems are affected first.

Feline Leukemia (FeLV) is the most common cause of cancer in cats, but it can also cause blood disorders and other issues too. The virus weakens the immune system of the affected cat, leaving them open to additional infections. A recently affected cat can also be susceptible to secondary infections.

Cats who have only been infected recently may not show any signs. However, over time, these cats will often display a decline in overall health. Symptoms may include:

  • Pale gums
  • Yellow coloring in the whites of eyes or mouth
  • Enlarged lymph nodes
  • Fever
  • Loss of appetite and weight loss
  • Poor coat or fur condition
  • Progressive lethargy and weakness
  • Skin, bladder, or upper respiratory infections
  • Diarrhea
  • Breathing difficulty
  • Reproductive problems
  • Stomatitis (oral disease)

Your cat may also experience some other signs and symptoms not mentioned here, particularly if they’re exposed to other ailments alongside the infection. You might notice sickness or a general inability to digest food well, or your cat’s behavior may change, leading to excessive grooming and isolation if they’re feeling unwell and anxious.

Paying close attention to any signs of cat behavior that seem abnormal for your feline is crucial for providing good care as a pet owner. This is particularly true when you consider that many serious ailments for cats, including Feline Leukemia (FeLV) may not show any symptoms straight away.

Your cat can be infected but not show any signs of the condition. However, if you allow that cat to interact with other cats or go outside, then it could be spreading the virus even further.

Diagnosing Feline Leukemia (FeLV)

Getting a diagnosis of Feline Leukemia (FeLV) is often relatively straightforward. Your vet will be able to determine whether your cat has the disease by conducting a special kind of blood test. The “ELISA” test identifies FeLV proteins in the cat’s blood. It’s a sensitive test that can identify cats with early signs of infection.

A secondary blood test, called the IFA, shows the progressive stage of the cat’s infection. Cats with positives here will probably be unable to clear the virus. The secondary test is generally conducted within a laboratory, rather than in the clinic for your vet.


If your cat identifies as positive for feline leukemia, try not to panic straight away. Remember that the first test can pick up very small strains of the virus. A false-positive test result is possible in kittens exposed to the virus in the womb, even if they’re not actually infected. The Feline Practitioners Association in America recommends testing kittens just in case. If a kitten tests positive for the virus, it may be crucial to separate this kitten from the rest of your cats.

If an older feline friend tests positive on the first test, you will need to isolate them from other cats to prevent the disease from spreading any further. Talk to your vet about having the test re-done and getting the IFA test (in the lab) as quickly as possible.

If both of the tests conducted are positive, then your cat probably has a Feline Leukemia (FeLV) infection. If the initial test is positive, but the IFA test is not, then your cat may be able to fight off the infection – even if they have it. Isolate your furry friend from other cats and get them retested within the next couple of months. With a little luck, the next test will come up negative. If it doesn’t, then you can go back to your vet and ask for advice on how to proceed.

What Happens After Cat FeLV Diagnosis?

The outcome of the two tests your vet conducts for FeLV will dictate what kind of suggestions they give for treatment and management. When your cat is exposed to feline leukemia, it’s difficult to say for certain what will happen next.

The virus spreads through the kitty’s body in the lymphocytes and monocytes, affecting the immune system. Within a few weeks, the condition starts to spread into the bone marrow. If the virus is able to set up a strong infection within the bone marrow cells, it will be very difficult for your cat to fight the infection off.

While immune responses will almost always develop against the FeLV virus, most cats will remain persistently infected with the condition. After an infection, several outcomes are possible:

  • Effective immune response: Some cats may be able to mount a successful immune system response that eliminates the virus in the cat quickly after exposure. These cats, which have recovered fully from infection, may become immune.
  • Regressive infection: A cat that launches a good immune response may be able to contain the infection effectively. Although the virus may be present within certain cells, an effective immune response will stop it from spreading any further. These cats may not develop any additional diseases or issues caused by Feline Leukemia (FeLV).
  • Uncontrolled replication: Many cats may be unbale to control the replication of the virus in the bone marrow. Cells in the marrow used to form new blood cells may be infected, and the virus will remain present in these cells, circulating cells, and in other places throughout the cat. These cats have persistent infections which may lead to further disease.
  • Atypical infections: In some rare circumstances, a cat may develop an unusual, localized infection, where partially effective immune responses allow a reduction of infection through the virus. However, replication may still appear within certain tissues.

What are the Outcomes of the Feline Leukemia Virus?

The exact results of a Feline Leukemia (FeLV) infection will differ depending on your cat. However, persistent infections will typically cause an ongoing state of immunosuppression. This means that your kitty will be more likely to suffer from additional ailments as a result of the infection.

Feline Leukemia (FeLV) can also frequently cause issues of anemia, which happens because the red blood cell precursors in the bone marrow are suppressed. Anemia accounts for about 25% of all of the diseases caused by FeLV.

Another potential outcome is Neoplasia, which is what happens when Feline Leukemia (FeLV) infection harms the DNA of the affected cells in your cat. This response leads to the development of tumors and may account for around 15% of all FeLV diseases. Although neoplasia is just one component of a potential FeLV infection, an infected cat is up to 50 times more likely to develop lymphoma.

In some cases, a variety of other diseases can occur within an infected cat suffering from Feline Leukemia (FeLV). The kind of disease or ailment that develops will depend on the strain of virus responsible for the infection. There are at least four different strains of FeLV in the world today, and each have a unique impact on the cat.

Although FeLV is a very serious disease with a potentially fatal outcome, it’s important not to lose hope as soon as you get a diagnosis. Remember that your cat can still live for several years with this condition, and you may be able to take steps to help them enjoy their life for longer. It’s also worth noting that there are many different kinds of infection, and some are more dangerous than others.

Treatments for Feline Leukemia (FeLV)

Sadly, there doesn’t appear to be any obvious treatment option available for FeLV. This is why around 85% of cats affected by the issue will end up passing away. Of course, regular veterinary checkups and careful preventative healthcare strategies can keep your cats feeling good for as long as possible. Physical examinations, testing, and parasite control prevent complications.


Since there’s no cure for Feline Leukemia (FeLV), management is mainly aimed at supportive and symptomatic therapy, including:

  • Prompt treatment and diagnosis: Treatment will be necessary whenever an additional infection appears. Immunosuppression will make it harder for your kitty to fight off any diseases or infections that come their way.
  • Good quality nutrition: Providing your cat with the right nutrition is always important. However, this is particularly crucial when supporting good health. Ask your vet whether additional supplementation is necessary. Although raw food might seem like a good idea at first, it could be problematic for Feline Leukemia (FeLV) cats, as they can’t fight off bacteria as well.
  • Maintaining preventative healthcare: Routine vet visits at least twice a year, combined with regular flea treatments, worming, and vaccination, is crucial.
  • Keeping them indoors: Vets will always recommend keeping a cat with a positive FeLV infection indoors. This will mean that infected cats are less exposed to other infections. At the same time, it reduces the spread of infection to other cats.
  • Supportive therapy: Some vets may suggest using blood transfusions and drugs to fight back against anemia. Certain vets will even offer chemotherapy to fight lymphomas that build as a result of Feline Leukemia (FeLV).

Depending on the situation, your vet may also recommend that you maintain a single cat household, if you don’t already have additional cats. In general, kitties with Feline Leukemia (FeLV) shouldn’t live alongside other cats. That’s because it’s so easy for this condition to spread through bodily fluids and saliva. Even sharing a bowl or litter box with another cat could spread the infection.

Even if you’re keeping your FeLV cat indoors (which you absolutely should), your vet may also suggest having them neutered. This will reduce the risk of your cat feeling as though they need to roam or fight.

Can You Protect Your Cat from Feline Leukemia (FeLV)?

It’s difficult to make absolutely sure that your furry friend will never be exposed to something dangerous, like Feline Leukemia. In an ideal world, we’d be able to give our cats vaccinations that would prevent them from falling victim to these issues. Unfortunately, that’s not something we’ve been able to do at this point.

Since there’s no direct treatment option for Feline Leukemia (FeLV), prevention is the best thing you can do. Keeping your cat away from other infected felines is the most crucial way of reducing the spread of the virus. Additionally, you can sometimes find vaccination options available from some vets for cats that are at high risk of exposure. However, it’s not guaranteed that this vaccination will be valuable for your cat. Even cats that have the vaccine will need to be regularly tested to check for exposure.

Ideally, you would keep your cat indoors to stop them from being exposed to other dangerous felines that may have the infection. Remember, it’s not always fighting that leads to this kind of infection, but any kind of friendliness and grooming too.

If your furry friend does turn out to be infected with FeLV then it’s your duty as a pet owner to ensure that they can’t make any other cats sick. Making sure that you don’t allow your cat to go outdoors after a positive diagnosis is essential. You should also avoid bringing any new cats into your house or introducing your cat to a multi-cat household.

Though you might not be able to stop your cat from getting Feline Leukemia (FeLV), keeping them indoors and out of the way of other potentially infected felines can reduce the risk significantly.

About the author

Rebekah Carter is a dedicated animal lover. Her Savannah cat, Roscoe, has a lot of attitude, while her Maine Coon, Dukino, is full of love. When not writing, she’s looking after her cats and researching ways to help them live their best possible life. Her passion for animals and natural skill for writing led her to pursue pet blogging.