What’s the most important thing you need to know before you bring a new cat home? In a previous blog, I talked about how to introduce new cats to each other. But first, I want you to stop by your veterinary clinic for a blood test—before your cats even meet or have physical contact!
That’s because there’s a highly contagious virus called feline leukemia (often called or abbreviated “FeLV”), and it’s really important to know your cat’s status for FeLV before you introduce cats to each other.
What shocks me as a veterinarian? I frequently ask cat parents if they know their cat’s FeLV or FIV status, and most assume their cat is negative but aren’t sure. While veterinarians often test for this, this is a test result you MUST know for your cat’s sake (I compare it to not knowing your partner’s HIV status). That’s because the diagnosis of FeLV dramatically affects your cat’s lifespan… from living to be a healthy 15- to 20-year-old cat to just a 2- or 3-year old cat.
So, what exactly is feline leukemia (FeLV)?
Feline leukemia is caused by a highly contagious retrovirus and is one of the deadliest viruses for cats. (Decades ago, it was one of the viruses used to study human retroviruses, such as HIV/AIDS). Feline leukemia affects your cat’s bone marrow and immune system (e.g., the lymphoid organs like the lymph nodes, thymus, spleen). Once this virus affects your cat’s body, it can result in cell mutation, cancer (such as lymphoma), and direct effects on the number of white and red blood cells in your cat’s body. This can result in leukemia and severe bone marrow suppression (e.g., anemia, immune deficiency). As a result, your cat’s body is more susceptible to infections, parasites, inflammatory problems, and whole-body (or “systemic”) effects.
As a veterinarian, I’ve had to break the news to cat parents that their cat has this deadly disease—and it’s so heartbreaking because FeLV has a really poor prognosis. Unfortunately, as a veterinary specialist, by the time I diagnose or see a cat with FeLV, it’s often too late. The signs are really severe and the disease has already ravished the body; sadly, pet parents only get a few days to weeks with their cat during the end stages of FeLV when I break the bad news. That’s why FeLV is one of my most hated diseases to diagnose as a veterinarian.
How common is FeLV?
Thankfully, I don’t see FeLV every single day. In fact, thanks to vaccination, testing, and pet parent education, I see this deadly feline virus less commonly than when I first started practicing (20+ years ago!). That said, it’s still estimated that 1-3% of cats in the United States are infected with FeLV. However, infection rates for FeLV go up dramatically (up to 30%) in ill or at-risk cats.
Which cats are at increased risk for FeLV?
Some cats are more at risk for FeLV: male cats and those that have outdoor access. Clinically, I also see kittens at higher risk for FeLV, as their immune system is weaker and more immature (due to their age). Kittens may have innocently gotten the infection from their mother.
What about cats that are less at risk for FeLV? Cats that live indoors and that are neutered or spayed are at less risk for FeLV. And those that are vaccinated for FeLV are at less risk! Next month, tune in for Part 2 to find out specific things you can do to prevent FeLV in your cats, and what you can do to keep your cats safe.
How do cats get FeLV? How is FeLV spread?
Unfortunately, feline leukemia is very contagious to other cats—especially from bite wounds or prolonged close contact to a FeLV+ cat. Cats get FeLV predominantly through bodily fluids such as saliva, milk, respiratory or nasal secretions, placental transfer, urine, blood, and, rarely, feces. Sources of exposure to FeLV include:
- Bite wounds (from exposure outdoors and fighting)
- Grooming each other
- Placental transfer
- Nursing
- Sexual transmission
- Using the same water and food bowls (less common)
- Using the same litter boxes (less common)
- Blood transfusions (rare)
Can I get FeLV from my cat?
While humans get retroviruses, FeLV is a feline-specific disease—so it cannot spread to humans.
What are the signs of FeLV in cats?
Depending on where FeLV is affecting the body, signs of feline leukemia in cats may include:
- Weakness
- Exercise intolerance
- Decreased appetite
- Weight loss
- Unkempt appearance or haircoat
- Fever
- Hypothermia (with severe symptoms, especially with anemia)
- Pale gums (e.g., anemia)
- Difficulty breathing
- Abnormal fluid in the chest cavity (e.g., pleural effusion)
- Tumors in the chest cavity (e.g., mediastinal tumors)
- Gastrointestinal signs (e.g., diarrhea)
- Ocular changes (e.g., inflammation of the eye)
- Generalized infections or inflammation in the body
- Enlarged lymph nodes
- Miscarriage or fetal death
- Death
How do you diagnose FeLV in cats?
As a veterinarian and cat parent, testing for FeLV/FIV is a MUST DO before your new cat steps one paw into your household. Why? Again, because this virus is so infectious—and I don’t want to expose any other house cats to it.
All cats should be tested for FeLV and all cat parents should know their cat’s results!
Your veterinarian will want to test your cat (or kitten) for this on your cat’s first veterinary visit. (If they don’t, look elsewhere!) Depending on your cat’s lifestyle, this test may need to be repeated annually (if your cat goes outside). The test for FeLV is a simple blood test. Please note that there are several types of blood tests, including the ELISA, IFA, and PCR. (There are also less common saliva and tear tests for FeLV, but these are not as accurate and are not recommended).
ELISA test
The most common blood test for FeLV is the ELISA test, which is readily available at any veterinary clinic or animal shelter. This test is very accurate and inexpensive to run, and you can get results back within minutes. (This blood test is typically in combination with the FIV or even feline heartworm test.) The FeLV portion tests for the presence of the virus (called p27) or its antigens (not antibodies, like the FIV test).
Please know that some animal shelters and breeders may test, but not all do. So, you always, always, always want to test (or re-test) your new cat as soon as you obtain them! If you just got a kitten, I often repeat the blood test a few weeks to months later for confirmation (around 6 months of age).
Next steps
If your cat tests negative for FeLV, that’s great news—a negative test is very reliable. However, if your cat was recently infected or exposed (e.g., after sneaking outside and getting into a cat fight), your cat should be re-tested at least 1-2 months after exposure.
If your kitten or cat tests positive for FeLV, your veterinarian will need to send out different blood tests—the IFA or PCR—to confirm the diagnosis. These are more specific tests that test for specific parts of the FeLV retrovirus or more advanced disease. (You should also keep your cat indoors only and isolated from other feline housemates until additional testing is confirmed.)
Please note that a cat shouldn’t be euthanized based solely on the initial diagnosis of FeLV, as no test is 100% accurate. We veterinarians need to interpret the test results based on your cat’s health, likelihood of infection, your cat’s ability to fight off the infection, persistent viremia, and confirmation of other tests! Some cats can seroconvert and go from a positive FeLV test to a negative test, so we need to re-test carefully, appropriately, and repeatedly.
My general rule
In the veterinary ER, the FeLV test is one of the first diagnostic blood tests that I run on a sick cat... especially if they are a younger, male, indoor/outdoor cat that occasionally scraps with other cats. Since the prognosis for feline leukemia is so poor, the FeLV is considered a “must-do” screening test. Plus, we know that infection rates for FeLV go up to 30% in ill or at-risk cats! Before I spend a pet parent’s money (which can add up to thousands of dollars in the veterinary ER) trying to save a cat, I beg of you: Make sure your cat has been tested for FeLV.
For me? My general rule is that any cat that you adopt, purchase, or rescue should always be tested for both FeLV and FIV before you even let them see your other cats. This is so important to keep your other cats safe and minimize disease spread. While it seems extreme, it really is for the sake of your other cats’ health!
When in doubt, talk to your veterinarian about feline leukemia, as you want to make sure to keep your cat(s) safe. Learn more with some great information from the Cornell Feline Health Center and the American Association of Feline Practitioners.
Will my cat fight off FeLV?
Most cats diagnosed with FeLV become symptomatic and die of FeLV-associated complications of anemia, infection, or cancer. Their body can’t contain or fight off the retrovirus, and the virus replicates aggressively in their lymphoid tissue and bone marrow.
As an emergency veterinary specialist, I most commonly see this when a cat comes into the veterinary ER for difficulty breathing, only to be diagnosed with abnormal fluid in the chest cavity or a large cancerous tumor growing in front of the heart (e.g., mediastinal mass). Sometimes, complications arise from a severe, life-threatening anemia due to FeLV attacking the bone marrow. Regardless, once clinical signs of FeLV develop, the prognosis is grave, and I’m often recommending humane euthanasia.
Less commonly, cats can be initially infected with FeLV and their immune system can fight it off. This can result in an “aviremic” state, where the virus isn’t in their body, so they are less likely to develop FeLV-related medical problems or shed the virus. This is less common, and when I do see it, it’s typically from a kitten that seroconverts to a negative FeLV state later.
How can I prevent my cat from getting FeLV?
Being that FeLV is often fatal, you want to prevent your cat from being exposed to this virus to begin with! The best way to prevent your cat from getting FeLV is by screening and testing all cats in your household at your veterinarian. Before you bring a new cat into the household, this common FeLV/FIV test is a must do. If your cats are negative, great!
Second, keep ALL your cats indoors. If you only let one of your five cats out, you’re still exposing the other four cats to infection! Keeping all your cats indoors prevents fighting with a stray neighborhood cat that may carry it. Need proof?
In a veterinary study looking at cats presenting to their veterinarian with skin infections or abscesses, more than 19% of cats were FeLV or FIV positive at the time of presentation. That’s 1 out of every 5 cats coming in for cat scratches or skin wounds! Cats develop abscesses when they fight with other cats—after all, their teeth and claws carry a lot of bacteria, resulting in a pus-filled abscess under the skin. If your cat has a skin abscess, not only does this require sedation, minor surgery, and antibiotics, but it also requires a FeLV/FIV blood test 30 and/or 60 days after the initial exposure of the retroviruses. This is to make sure your cat didn’t catch these deadly viruses. And based on the data, there’s potentially a 1 in 5 chance your cat may get FeLV from this!
The FeLV vaccine
The next way of protecting your cat? Keeping your cat vaccinated with the FeLV vaccine. The FeLV vaccine is a must for all kittens, as we want to make sure we protect kittens early—especially when their immune system is more immature due to youth. That said, while the FeLV vaccine is safe, it’s considered a non-core vaccine—in other words, not all adult cats need it as they age and mature. Also, keep in mind that the FeLV vaccine is not 100% protective (as compared to other feline vaccines, which are almost 99% effective). The best way of protecting your cat is also by minimizing exposure to FeLV-infected cats.
So, when do I recommend the FeLV vaccine? I recommend the FeLV vaccine in these cases:
- Kittens
- Cats that go outside
- Cats that live with cats that go outside
- If you foster cats
- Cats living with FeLV+ cats
- If you have a lot of environmental turnover of cats (e.g., shelter work, etc.)
- Cats living in shelters or group housing (e.g., catteries)
Know that vaccinating your cat for FeLV does not affect the blood test for your cat. (This is different from the FIV vaccine, which does make your cat test positive for FIV despite protecting their immune system; hence, why the FIV vaccine is not commonly recommended or used.) That said, cats ideally should be blood tested for FeLV prior so we know if your cat was exposed. If your cat already has tested positive for FeLV, there is no benefit of getting the vaccine.
My cat was just diagnosed with FeLV. What should I do?
If your cat was just diagnosed with FeLV, first, my heart goes out to you. It’s a devastating disease and can be very stressful to deal with.
Cats diagnosed with FeLV should be kept indoors only to prevent the spread to other cats. If you have other cats in the household, ideally, you should isolate the FeLV+ cat from the other cats. This is to maximize all your cats’ health and to prevent spread of this virus to your other cats—and to prevent your cats from spreading infections to your now immunosuppressed FeLV+ cat. Your other cats in the household should also be tested for FeLV to make sure they are negative. Depending on when your FeLV+ cat was diagnosed, I typically do this at the time of diagnosis and follow up a few months later with a second blood test in all the remaining cats.
If you do have other cats in the household, I also recommend disinfection of the environment. Thankfully, FeLV as a virus isn’t super hardy outside of your cat’s body—it’s estimated to only survive for a few hours outside of a cat’s body. That said, I recommend disinfecting what you can, especially water and food bowls, kitty litter boxes, etc., with a dilute bleach solution or disinfectant. Then, isolate your FeLV + cat from your other cats to prevent exposure.
Keeping your FeLV+ cat healthy
If your cat was diagnosed with FeLV, you want to keep your cat as healthy as possible. This includes:
- Physical examinations 2-4x a year
- Preventative medication
- Blood work monitoring (to make sure they aren’t getting anemic or getting an infection)
Keeping your cat as healthy as possible once they are diagnosed with FeLV is really important, since there’s no cure for FeLV. While certain medications like steroids, anti-virals, and interferon have been evaluated for the treatment of FeLV, none have been very successful.
Most importantly, help minimize the chances of your cat developing secondary infections, since FeLV cats have a weaker immune system. This includes:
- Keeping your cat inside
- Isolating your cat from other cats in the household
- Monitoring your FeLV+ cat for clinical signs like pale gums, not eating, difficulty breathing, and weight loss
- No fostering or cats/kittens or introducing new pets into the household, as we don’t want them catching anything
If you notice any clinical signs, you want to seek veterinary attention immediately for treatment, since your cat will need more care for their weakened immune system. There are some treatments for specific problems—like antibiotics for an infection, fluids under the skin for dehydration, appetite stimulants for loss of appetite, and blood transfusions for anemia—but again, there is no direct cure for FeLV.
What’s the prognosis for FeLV? How long will my cat live with FeLV?
Unfortunately, the prognosis for a cat with FeLV is poor. This virus will result in the quick demise of your cat. Personally, I’ve never seen a cat live past 5 years of age with it, as most FeLV+ cats can only live with this for 2-3 years after the time of diagnosis. (This is different from how long your cat can live with FIV, which can potentially be a decade or more!)
When in doubt, talk to your veterinarian about living with FeLV. And try to keep all your feline family members as safe as possible!
