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hlrobin posted:
Found a kitten and want to adopt, but he has tested positive for FeLV. He is about 10 weeks old. My vet wants to re-test at 6 months of age. The kitten is seemingly healthy at this point. What do you think?
Violets_are_Blue responded:
Sometimes, when a mother is Felv positive, the antibodies or antigens (what the body makes to try and protect itself from viruses and what most Felv tests look for) she makes pass along to her kittens through the placental bond or through her milk. It doesn't mean the kitten has the virus, it just means that the kitten has some sort of antibody or antigen for it. Retesting at 6 months is a standard procedure for these kittens as that is when there should not any more of the mother's antibodies left in their body. Should you adopt him? It's up to you. Do know that there still is a chance he could have the virus and look up what that could mean in the long run. Only commit to him if you can commit to a cat who may have a chronic issue.
srstephanie replied to Violets_are_Blue's response:
Hi Violets are Blue and hlrobin,

I'm not a vet or tech, but I've listened to a number of talks given at vet CE conferences by some of the top veterinary specialists and researchers ... including Dr Richard Ford of NC State and Dr Susan Little who is a feline specialist and a co-author of both the 2008 AAFP Feline Retrovirus Management Guidelines and also the newly published 2011 Canadian FeLV/FIV Testing Guidelines. The Canadian Guidelines are not yet available online, but the 2008 AAFP Guidelines can be found here (there are links for both the full Guidelines and also a "Summary" form for pet owners):

I think you may be a bit confused about antibodies and antigen. While kittens get antibodies from their mother ... which can interfere with testing for FIV because all FIV tests look for antibodies, that isn't true of antigen. The FeLV tests are looking for the p27 antigen which is produced by the actual virus. So, if it is detected in a kitten, it is a sign of infection. Maternal antibodies do not interfere with FeLV testing. Here is a quote from the 2008 Guidelines:

"Kittens may be tested at any time because passively
acquired maternal antibody does not interfere
with testing for viral antigen. However, kittens
infected as a result of maternal transmission
may not test positive for weeks to months after
birth (Levy and Crawford 2005)."

However, FeLV is a VERY complex disease. Within about a month of exposure to FeLV the p27 antigen will be found in circulation. The most common screening test, the ELISA (or in-clinic "SNAP") test looks for the circulating p27 antigen. I would assume that is the test that hlrobin's kitten tested positive on.

After initial infection, a very small number of kittens may actually clear the infection. So, if the SNAP test was done during that period, it is possible that the kitten will not be permanently infected.

But that is now thought to be rare. More often, the FeLV goes on and infects cells ... blood cells and particularly bone marrow lymphocytes. There is another test for FeLV called the IFA that looks for the p27 antigen INSIDE of the blood cells. This is a more advanced stage of infection than what the SNAP test is looking for.

When there is an initial positive for the SNAP test, the Retrovirus Guidelines recommend immediate retesting using the IFA test. However, since the IFA is looking for a more advanced form of infection, and it may take 6-8 weeks after the initial infection before the blood cells are infected, it might be better to wait a month or so for the IFA test, or test both now and in a month or two. If the kitten is negative now on the IFA, it may simply mean that the infection hasn't progressed yet to the blood cells, and not that the kitten is not infected.

It gets even more difficult. Once the lymphocytes are infected, the FeLV deposits its RNA inside the cell. Then, the FeLV RNA turns itself into DNA (called DNA provirus) ... and then incorporates itself into the cats genome. At that point, it becomes part of the cat and there is no cure.

Then, for many cats, the infection becomes "regressive" ... i.e. it becomes dormant and "hides" in the cats DNA ... and at that point both the SNAP & IFA tests would be negative, even though the cat is infected. Some cats may remain healthy for years or life. In others, perhaps years later, the FeLV will reactivate (become "progressive") and cause infection ... resulting in depressing the immune system and making the cat susceptible to many diseases.

It is hard to interpret FeLV tests because one doesn't know the stage of disease at testing. One other test, the PCR, can detect the provirus and may be the best way to know if the cat is infected ... but you have to be careful to use a good lab for the test and make sure their tests have been validated.

Many cats live years with FeLV and I hope you can give this one a home. Good luck.

Stephanie in Montreal
Drew Weigner, DVM, ABVP responded:
This can be quite complicated, but in a nutshell:

A positive test means he has FeLV virus circulating in his bloodstream (it doesn't test for antibodies, but the presence of the virus itself.) Unfortunately, there's a good chance the kitten will still be positive at six months of age but it is still recommended to retest him then. If he tests positive again, he is persistently infected with Feline Leukemia. There is also a confirmatory test (called an IFA test) that may be slightly more accurate. Many of these kittens are clinically normal for several years but eventually succumb to the disease. If he's negative, he's likely cleared the infection (and may be immune) but a small number that test negative hide the virus in the bone marrow which could reactivate at a later date (and become positive again.) As long as he tests negative, he's not contagious to other cats and should live a healthy life.

If he stays positive, he should be kept indoors away from other cats as his immune system won't work well. This not only keeps him from infecting other cats but also limits his exposure to other diseases he may have difficulty fighting off. This is easy if you don't have other cats and I have several clients with single, positive cats that have a good quality of life.

Drew Weigner, DVM, ABVP
The Cat Doctor
Board Certified in Feline Practice


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