Vet-Approved Content
The more we learn about feline leukemia (FeLV), the more complicated it gets to advise cat lovers on the dangers of having an FeLV-positive cat in your home with other cats who don’t have the disease.
Testing for feline leukemia can be complicated. The progression of the disease can be highly variable.
The safest answer, of course, is to have healthy, FeLV-negative cats not get exposed to FeLV-positive cats. But life isn’t always that simple.
Here are some scenarios I’ve been faced with from cat-loving clients:
- A son or daughter must move back home with Mom and Dad. The adult child has a healthy, happy, leukemia-positive cat. “Please, Mom, let me bring Tigger home. I’l keep him locked in my room away from Bugger. I can’t give this cat up.” What does Mom say?
- You and your new roommate both have happy, healthy cats. You come to find out your roomie has not brought her cat to a veterinarian for several years. You get fleas in your apartment. The roomie goes to the vet to get flea medicine. The vet recommends the cat be tested for the retroviruses, FeLV and FIV (feline immunodeficiency virus). This 4-year-old, sweet, healthy-looking cat comes back FeLV-positive. Do you throw your roommate out, or weigh other options?
- You have 3 indoor cats at home who are leukemia-negative. You fall in love with a kitten who’s been tested leukemia-negative by the shelter you volunteer at. You bring Snookies home, and the cat integrates into your household beautifully. In a month, you go back to your vet for follow-up vaccinations, and she suggests testing for feline leukemia again, just to be safe, since the early test may be a false negative. Snookies comes back FeLV-positive. What do you do?
- Your cat tested positive for leukemia 10 years ago and is still healthy. You have a new boyfriend with a cat, leukemia-negative, who is ready to move in. What do you do?
Testing for Feline Leukemia Virus
In order to get a final answer, you may have to do sequential tests and wait periods of time between testing a cat for the feline leukemia virus.
Each test requires a simple blood sample. There is no invasive testing for FeLV.
ELISA (SNAP) Test
This is the quick blood test done in the vet’s office. It is now recommended to run this test on serum, not whole blood. You will get the answer in a few minutes.
If the ELISA test is negative but the cat is very young or has an unknown or feral background, it’s advised to run this test again in a few weeks. There is a chance the cat could have been exposed but is not positive yet on the first test.
A second negative ELISA test should reassure you that the cat is truly negative.
What If My Cat Tests FeLV-pPositive?
If the result is a positive on the ELISA, don’t despair.
It is recommended to do a follow-up blood test sent to a lab, either a PCR or IFA. If either of these tests comes back positive, the cat most likely has FeLV and will become clinically ill anywhere from a few months to a few years.
Discordant Cats
Despite all the testing, some cats can continually test positive on the ELISA but continue to be negative on the IFA.
This means the cat is infected, but the FeLV virus is sequestered in the body and not yet in the bone marrow. This is called a discordant infection.
Over time, 25% of these discordant cats will have progression infection, 25% of them will turn negative and 50% will remain discordant.
Most FeLV experts believe these discordant cats are potentially infectious to other cats.
So, can your vet give you a clear answer and tell you what exactly will happen along with the risks? The answer, even with decades of research on this disease, remains muddy.
Risk Factors for Feline Leukemia
The possible transmission of the disease from cat to cat in a household is variable.
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Many cats develop a natural immunity to the feline leukemia virus as they age. If you have an older, FeLV-negative cat, the risk for them to become infected when exposed to FeLV-positive cats decreases.
The amount of contact between cats also determines risk.
As far as we currently know, the virus does not live long in the environment. Close contact like cat fighting or excessive grooming of each other heightens the risk.
If there is an FeLV-positive cat in the household who never gives the other cats in the household the time of day, the risk of transmission decreases.
Protection and the Feline Leukemia Vaccine
Any cat with the potential to come into contact with an FeLV cat should be vaccinated.
If you bring a cat who’s FeLV-positive into your household or have an indoor/outdoor cat, vaccinate the negative cat with a leukemia vaccine.
Experts differ a bit on how frequently this vaccine should be boosted.
In my opinion, it’s great to weigh the cost/benefit/exposure in all these situations:
- The initial 2 series of the FeLV vaccine gives the normal, healthy cat a long-lived protection.
- If the cat will be going outside and possibly meeting up with an FeLV-positive cat or is living with an FeLV-positive cat, you might want to boost the vaccine every 3 years. Talk to your vet. I, for one, want to protect but not over-vaccinate.
- The FeLV vaccine is effective. Can it give you 100% protection and reassurance that your cat cannot contract FeLV? No, but it’s a great help.
Here’s an FeLV-positive cat who is looking for his forever home:
A Personal Story
When I was in college, both my roommate and I had indoor house cats.
Her cat Japonica, was a lovely 10-year-old Siamese who had always been an indoor cat.
Japonica began to show signs of illness and, surprisingly, she was FeLV-positive. We have no idea when she contracted it or how long she had been positive.
Our 2 cats didn’t particularly care for each other (selfish and snooty felines!), but we did not know what to do. I had my cat tested, and she was negative.
We decided to risk it and let the cats continue to live in the same apartment. My cat never contracted the disease, but it was a difficult decision nonetheless.
When family or friends are faced with mixing FeLV-negative cats and FeLV-positive cats in the same household, there’s no simple answer.
- Speak with your vet about the cats’ ages and the feline dynamics involved.
- Do all the testing recommended.
- Vaccinate the negative cats.
- Have a heart-to-heart talk with the people involved.
In the end, if you think it would devastate you to have your FeLV-negative cat become positive, don’t take the risk.
This pet health content was written by a veterinarian, Dr. Debora Lichtenberg, VMD. It was last reviewed Oct. 17, 2018. 
