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Feline Leukemia Virus (FeLV) Education

Are you an owner of a FeLV+ cat?  Please take our research survey here

Check out our blog for even more information on FeLV, FIV, and stories about our cats!

My cat just tested FeLV+, what do I do?!

The first and hardest step is don't panic. One positive test result (especially on the in-house SNAP test), is not enough to confirm a FeLV infection. Any positive test should be confirmed with another type of test, and repeated in 30-60 days. Even if your cat does turn out to be persistently infected, it is not a death sentence. Many FeLV+ cats can live happy, healthy lives for years after their diagnosis.

What is FeLV? 

Feline Leukemia Virus (FeLV) is a retrovirus that affects cats by suppressing the immune system. It is not the same thing as FIV, and the terms are not used interchangeably. For more information on the difference between FeLV and FIV, please visit our blog here. For more information about FIV, please go here. Of the two, FeLV is the more serious and is more easily transmitted than FIV. Humans and other animals cannot catch FeLV or FIV. Read more here

What are the "stages" of a FeLV infection?

When a cat is exposed to feline leukemia, there are several ways that the disease might progress. 

  1. Some cats will not be infected due to inadequate exposure and a good immune response. 

  2. Some cats will develop a latent or regressive infection; these cats will not be able to destroy all of the virus, but will be able to hold it in check. The virus integrates into the cat's own DNA but is not active. These cats show no signs of infection and usually do not shed virus in their saliva or other body secretions. However, the infection can later become active again, especially if the cat becomes stressed or immunocompromised. 

  3. Some cats will become persistently infected; these cats will not develop an adequate immune response and will remain permanently infected with FeLV. This is called a progressive infection. These cats will shed large amounts of virus in their saliva and often develop FeLV-associated diseases within a few years.

Read more about the progression/stages of FeLV here and here.

How is FeLV transmitted?

The virus is shed in very high quantities in saliva and nasal secretions, but can also be found in urine, feces, and milk from infected cats. FeLV is most often transmitted between cats by a bite wound or during mutual grooming. It is less commonly transmitted through shared food and water bowls or (even more rare) shared litter boxes. It takes a large amount of virus to infect an adult cat, so usually prolonged contact is necessary. Transmission can also take place from an infected mother cat to her kittens, either before they are born or while they are nursing.

FeLV doesn't survive long outside a cat's body—no more than a few hours under normal household conditions. Once the bodily fluid containing the virus dries, the virus typically can no longer survive and be passed on. 

Kittens younger than 6 months of age are most susceptible to the virus, as their immune system has not yet fully matured. Adult cats with normal immune systems have a much better chance of fighting off the virus when exposed. An unvaccinated adult cat has roughly a 50% chance of contracting the disease when exposed, and a properly vaccinated adult cat has roughly only a 2% chance of contracting the disease when exposed (depending on the type of vaccine used - see the section below on vaccines for more information). 

Read more about transmission. 

How serious is it?

Feline Leukemia can affect a cat in several ways. FeLV can cause cancer, various blood disorders, and weaken the immune system, leaving the cat susceptible to other infections. However, a diagnosis of FeLV should not mean an automatic death sentence. Many cats can and do live normal, happy lives for years after the diagnosis. Read more about Feline Leukemia misconceptions here

The severity of illness caused by FeLV varies greatly from cat to cat. The age at which a cat is infected has a pronounced effect on the severity and progression of the virus. The virus tends to be harder on kittens, and most kittens die from the effects of the disease by the time they are two years old. However, cats that are infected as adults have a much better chance of remaining healthy for years without showing any symptoms, and can live a more normal lifespan (10-15 years). 

What are the symptoms of FeLV?

During the early stages of infection, it is common for cats to exhibit no signs of disease at all. However, over time—weeks, months, or even years—the cat's health may progressively deteriorate or be characterized by recurrent illness interspersed with periods of relative health. Signs can include:

  • Loss of appetite
  • Slow but progressive weight loss, followed by severe wasting late in the disease process
  • Poor coat condition
  • Enlarged lymph nodes
  • Persistent fever
  • Pale gums and other mucus membranes
  • Inflammation of the gums (gingivitis) and mouth (stomatitis)
  • Infections of the skin, urinary bladder, and upper respiratory tract
  • Persistent diarrhea
  • Seizures, behavior changes, and other neurological disorders
  • A variety of eye conditions
  • In unspayed female cats, miscarriage of kittens, or other reproductive failures

Read more here

How is it diagnosed?

There are two types of tests commonly used to diagnose FeLV: the ELISA test and the IFA test.

  • ELISA: (Enzyme-Linked Immunosorbent Assay) This is the test that is commonly performed in-house at your vet's office. The most commonly used ELISA test is the SNAP test from IDEXX. This test detects a protein produced by the virus circulating in the blood, indicating that the virus is circulating in the bloodstream. A positive result on this test indicates exposure to the virus, but not the stage of infection. This test does not detect antibodies to FeLV, and is not typically affected by prior FeLV vaccination. 
  • IFA: (Immunofluorescent Assay): This test is performed by a laboratory, so a blood sample usually has to be sent away. The IFA test looks for proteins produced by the virus inside of cells in the bloodstream. A positive result on this test indicates that the virus has infected the cat's bone marrow and is persistently infected. 

The main thing to keep in mind is that one positive result on one test it not sufficient to diagnose a cat with FeLV. Any positive ELISA test should be repeated. If a cat tests positive on an ELISA test, it is recommended that an IFA test be performed immediately. The combined results can then give you an idea of how to proceed.  If the ELISA and IFA tests are both positive, then the cat is likely persistently infected.  If the ELISA test is positive, but the IFA is negative, this is called a discordant result.  A discordant result can mean that the cat was recently exposed to the virus, and they may still be able to mount an effective immune response and fight off or suppress the virus.  In the case of a discordant result, the cat should be isolated until both tests can be repeated in 30-60 days. 

Have an interesting testing story? Share it in our survey!

Read more about the steps to take when testing for FeLV. 

Read more about the IFA test. 

When should my cat be tested?

In 2008, The American Association of Feline Practitioners (AAFP) released new guidelines for FeLV testing. They recommend that all cats be tested for FeLV. In addition, cats should be (re)tested:

  • During sickness: Regardless of previous negative results. While many signs (such as fever, stomatitis, vomiting, and diarrhea) are obvious indicators of illness, other signs are subtle and may include changes in behavior, grooming, and eating habits.

  • When being adopted/entering new home: Regardless of age and whether or not they will be entering a household with other cats. They should be tested prior to being introduced into the household.

  • When living in multi-cat households in which another cat is infected with FeLV, or are otherwise at high risk (e.g., cats that go outdoors unsupervised).

  • After potential exposures: When cats have had known or possible exposure to other cats who are infected or are of unknown infection status. If a negative test is obtained, the test should be repeated after a minimum of 30 days.

  • Prior to initial FeLV vaccination. FeLV vaccine should not be given to FeLV infected cats.

Read more here. 

How accurate are the tests?

No test is (or ever will be) 100% accurate, but the current tests for FeLV are generally very good. The ELISA SNAP test is a good screening test, but a positive result should always be confirmed by another type of test (like IFA), as false positives can occur. *Note: There have been a number of reports that the SNAP triple test (which tests for FeLV, FIV, and heartworms) has a high rate of false positives. Calvin's Paws has experienced this first hand, and we no longer use the triple tests for this reason. We use the Combo SNAP test, which looks for FIV and FeLV. 

Another problem with testing accuracy is that a negative test result does not necessarily mean that a cat is not infected with the virus. A negative test result can actually mean 3 things: 

  1. The cat has never been exposed to FeLV and does not have the virus (this is by far the most common). 
  2. The cat was exposed to FeLV very recently, and there are not enough virus particles for the test to detect. The cat may test positive at a later date. 
  3. The cat was exposed to FeLV, but overcame the infection or has a regressive (latent) infection. Cats with regressive infections are not shedding the virus and cannot infect other cats. However, regressive infections can become active again when the cat is stressed. *Note: Cats with regressive infections may test negative on BOTH the ELISA and the IFA test, so they can be almost impossible to identify. There is some emerging research that regressive infections can be detected using a third test called PCR to look for viral DNA/RNA in the blood, but this is not endorsed by the AAFP.

A note about FeLV testing in kittens: The AAFP recommends testing all kittens, regardless of age. It is common to assume that all kittens born to an infected mother will also be FeLV+, but this is not always the case. In some cases, the kittens will have small amounts of the viral protein that ELISA tests look for circulating in their blood, but may not actually be infected with the virus. Any kitten that tests positive should be retested in one month, and again at 6 months and 1 year of age. If they eventually test negative, then they do not have the virus. 

Read more about testing accuracy:



Testing in Kittens: http://bestfriends.org/News-And-Features/News/Feline-leukemia-misconceptions/

Can it be prevented?

There are several vaccines against FeLV that are available. Depending on the type of vaccine used, research says that they are 85%-98% effective, but no vaccine is 100% effective. You can read more about recent research on vaccine effectiveness here. So while the chances of a vaccinated cat contracting FeLV are slim, there is always some risk. 

The AAFP does not consider the FeLV vaccine to be a "core" vaccine for all cats. However, vaccination is recommended when a cat is at an increased risk of exposure. FeLV vaccination should be considered for cats that live with FeLV+ cats or cats of unknown status and cats that go outside and/or fight. The AAFP does encourage the vaccination of kittens. 

Read more about a study on the different types of vaccines. 

Can it be treated?

There is no treatment for FeLV, but it can be managed. Cats with FeLV should be monitored for signs of common illnesses (upper respiratory infections, gum disease, etc.), as these can become more serious in cats with weakened immune systems. Like all cats, FeLV+ cats should be checked by a vet at least once a year, and your vet may recommend performing routine blood work to get a full picture of the health of your cat. 

Read more about managing FeLV. 

Read EVEN MORE about managing FeLV. 

How does Calvin's Paws handle cats that test positive for FeLV? 

Calvin's Paws currently has several  cats that are persistently infected with Feline Leukemia. They are all in a foster home in a low-stress environment. They receive all routine vet care and check-ups, and are monitored for any "opportunistic" infections. All of these cats are very sweet, social, and easy to please , and they would just love to find a forever home of their own. All of our FeLV+ cats are available for adoption, we just recommend that they only go to a home with no other cats or only other positive cats.  If you have a cat that has tested positive for FeLV, and want another cat but are afraid of FeLV transmission,  please consider adopting another FeLV+ cat! Check out our FeLV+ kitties here