Feline leukemia, or FeLV, is a viral disease that affects cats. It can be transmitted through bites and scratches from an infected cat. This virus is contagious to both humans and other animals.

Feline leukemia is a virus that can be passed from cats to other cats. It can also be passed to humans, but it’s rare. Kittens born with feline leukemia are usually taken care of by their mother for the first few weeks of their life.

Dr. Justine Lee’s article was published on October 6, 2021.

Dr. Justine Lee, DACVECC, DABT, covers all you need to know about Feline Leukemia (FeLV) in cats in this two-part blog. She’ll go through what FeLV is, how it’s spread, and what the symptoms are. Please check in next month for Part 2 to learn how to avoid it and what you need to know as a cat parent to keep your cat(s) safe! 

What is the most crucial information you should have before bringing a new cat into your home?

I discussed ways to introduce new cats to each other in a previous blog. But first, I’d want you to have a blood test at your local veterinarian clinic—before your cats ever meet or have physical contact!

That’s because feline leukemia (also known as or shortened “FeLV”) is a highly infectious virus, and it’s critical to know your cat’s FeLV status before introducing cats to one other. 

As a veterinarian, what surprises me? When I question cat owners whether they know their cat’s FeLV or FIV status, the majority believe their pet is negative but aren’t sure. While vets often test for this, you must know the results for the sake of your cat (I equate it to not knowing your partner’s HIV status). Because FeLV diagnosis reduces your cat’s lifetime from a healthy 15- to 20-year-old cat to only 2- or 3-year-old cat. 

So, what is feline leukemia (FeLV) exactly?

Feline leukemia is one of the most deadly diseases for cats, since it is caused by a highly infectious retrovirus. (It was formerly one of the viruses used to research human retroviruses like HIV/AIDS.) The bone marrow and immune system of your cat are affected by feline leukemia (e.g., the lymphoid organs like the lymph nodes, thymus, spleen). Once this virus has infected your cat’s body, it may cause cell mutations, cancer (such as lymphoma), and direct impacts on the amount of white and red blood cells in his or her body. Leukemia and severe bone marrow suppression may develop as a consequence of this (e.g., anemia, immune deficiency). As a consequence, infections, parasites, inflammatory issues, and whole-body (or “systemic”) impacts are more likely in your cat’s body.

As a veterinarian, I’ve had to inform cat owners that their cat has FeLV, which is sad since the illness has such a terrible prognosis. Unfortunately, as a veterinary expert, it’s frequently too late by the time I identify or see a cat with FeLV. The symptoms are severe, and the illness has already ravaged the body; unfortunately, when I deliver the terrible news about FeLV, pet owners only have a few days to weeks with their cat. As a veterinarian, this is why FeLV is one of my least favorite illnesses to diagnose.

What is the prevalence of FeLV?

Thankfully, I don’t come across FeLV every day. In fact, due to immunization, testing, and pet parent education, I encounter this fatal feline illness much less often now than when I first began practicing (20+ years ago!). Despite this, it’s believed that 1-3 percent of cats in the United States have FeLV infection. FeLV infection rates, on the other hand, rise significantly (up to 30%) in sick or at-risk cats. 

Which cats are at a higher risk of FeLV infection?

FeLV is more common in male cats and cats that have access to the outdoors. In my practice, I’ve seen that kittens have a greater chance of contracting FeLV since their immune systems are weaker and more immature (due to their age). It’s possible that kittens caught the illness from their mother unintentionally. 

What about cats that aren’t as susceptible to FeLV? FeLV is less likely to infect indoor cats that have been neutered or spayed. Those who have been vaccinated against FeLV are also at a lower risk! Tune back next month for Part 2 to learn about specific measures you can take to prevent FeLV in your cats and how to keep them safe.

FeLV is transmitted to cats in a variety of ways. How does FeLV go around?

Unfortunately, feline leukemia is very infectious among cats, particularly when transmitted via bite wounds or continuous close contact with a FeLV+ cat. FeLV is transmitted to cats mostly via body fluids including saliva, milk, respiratory or nasal secretions, placental transfer, urine, blood, and, in rare cases, feces. FeLV may be contracted from a variety of sources, including:

  • Wounds caused by bites (from exposure outdoors and fighting)
  • Taking care of each other
  • Transfer of the placenta
  • Nursing
  • Transmission of sexually transmitted diseases
  • The identical water and food dishes were used (less common)
  • Continuing to use the same litter boxes (less common)
  • Transfusions of blood (rare)

Is it possible for me to get FeLV from my cat? 

While humans may acquire retroviruses, FeLV is a feline-only illness that cannot be transmitted to humans. 

What are the FeLV symptoms in cats?

Signs of feline leukemia in cats may vary depending on where FeLV is affecting the body:

  • Weakness
  • Intolerance to exercise
  • Appetite decreases
  • Loss of weight
  • Haircoat or untidy look
  • Fever
  • Hypothermia is a condition in which a person becomes cold (with severe symptoms, especially with anemia)
  • Gums that are pale (e.g., anemia)
  • Breathing problems
  • Fluid in the chest cavity that is abnormal (e.g., pleural effusion)
  • Chest tumors are cancerous tumors that develop in the chest cavity (e.g., mediastinal tumors)
  • Symptoms of the gastrointestinal tract (e.g., diarrhea)
  • Changes in the eyes (e.g., inflammation of the eye)
  • Infections or inflammation all throughout the body
  • Lymph nodes that have grown in size
  • Miscarriage or fetal death are also possible outcomes.
  • Death

How can you know if your cat has FeLV?

Testing for FeLV/FIV is a MUST DO as a veterinarian and cat parent before bringing your new cat into your home. Why? Because this illness is so contagious, I don’t want to risk infecting any other house cats. 

FeLV testing should be done on all cats, and all cat owners should be aware of their cat’s findings!

On your cat’s first veterinary appointment, your veterinarian will want to test your cat (or kitten) for this. (If they don’t, go somewhere else!) This test may need to be performed yearly depending on your cat’s lifestyle (if your cat goes outside). FeLV is detected via a simple blood test. Please keep in mind that blood tests come in a variety of forms, including ELISA, IFA, and PCR. (Saliva and tear tests for FeLV are also available, but they are less reliable and are not advised.) 

ELISA (Enzyme-Linked Immunosorbent Assay

The ELISA test, which is easily accessible at any veterinary clinic or animal shelter, is the most frequent blood test for FeLV. This test is very accurate and cheap to do, with results available in minutes. (This blood test is often used in conjunction with FIV or even feline heartworm testing.) The FeLV component looks for the virus (also known as p27) or its antigens (not antibodies, like the FIV test). 

Please be aware that although some animal shelters and breeders may conduct tests, not all of them do. As a result, you should always, always, always test (or re-test) your new cat as soon as possible! I frequently repeat the blood test a few weeks to months later for confirmation if you recently acquired a kitten (around 6 months of age).

Steps to take next

It’s excellent news if your cat tests negative for FeLV; a negative test is highly dependable. If your cat was recently sick or exposed (for example, after slipping outdoors and getting into a cat fight), your cat should be tested again at least 1-2 months later.

If your kitten or cat tests positive for FeLV, your veterinarian will need to order further blood tests to confirm the diagnosis, such as the IFA or PCR. These tests look for particular components of the FeLV retrovirus or signs of more severe illness. (You should also confine your cat to the home and separate him from other felines until further testing is completed.)

Please keep in mind that no test is 100 percent correct, therefore a cat should not be killed based only on the first FeLV diagnosis. We doctors must interpret the test findings depending on your cat’s health, the probability of infection, the capacity of your cat to fight the illness, chronic viremia, and the results of other tests! We must re-test properly, responsibly, and frequently since some cats may seroconvert and move from a positive FeLV test to a negative test. 

My basic guideline is this:

The FeLV test is one of the first diagnostic blood tests I perform on a sick cat in the veterinary ER… particularly if it’s a younger, male, indoor/outdoor cat that sometimes scrapes with other cats. FeLV is regarded a “must-do” screening test since the prognosis for feline leukemia is so dismal. Furthermore, we know that FeLV infection rates in sick or at-risk cats may reach 30%! Be sure your cat has been tested for FeLV before I waste a pet parent’s money (which may mount up to thousands of dollars in the veterinary ER) attempting to rescue a cat. 

What about me? My general guideline is that every cat you adopt, buy, or rescue should be tested for FeLV and FIV before being allowed to interact with your other cats. This is critical in order to protect your other cats and prevent illness transmission. While it may seem severe, it is for the benefit of the health of your other cats!

When in doubt, see your veterinarian about feline leukemia to ensure the safety of your cat(s). The Cornell Feline Health Center and the American Association of Feline Practitioners provide some excellent resources.

Keep an eye out for Part 2 next month. I’ll go through ways to avoid FeLV infection and what you need know as a cat parent to keep your cat(s) safe from this infectious illness.




Feline leukemia is a disease that can be passed on to cats by infected animals. It is the final stages of feline leukemia that are usually fatal for cats.

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