As if new grads don't have enough to deal with, I got the added bonus of very nearly euthanizing my healthy cat!
When my husband and I moved back in together in May, we combined our cats for the first time. I had Mama and Cas, and he had Roosevelt. He adopted Roosevelt from a shelter in Spokane, Washington in December 2012 and had kept him as an indoor only, single kitty in his apartment for a year and a half. In mid-August, my benefits kicked in and through Banfield as a part of my contract I get three of our Owner Wellness Plans. I brought Roosevelt in as the first of the three to booster his vaccines, run blood work, and do a dental cleaning. I received a nasty shock when he turned up weakly FeLV+ on an ELISA snap test. I thought it was probably a false positive, so I ran it again. Same result.
I panicked, raced home to grab my two cats, brought them in and tested them. Both tested negative, and I vaccinated them right away.
Don and I had a serious conversation that night about the risk Roosevelt posed to my cats, even with them vaccinated, and how very bad FeLV was. I told him that even vaccinated, I wasn't prepared to risk losing Mama or Cas to this disease. He was ready to euthanize Roosevelt right then, but I asked him to let me submit an IFA as a confirmatory test, because Roosevelt's history just didn't fit with this disease.
Feline leukemia virus stats are a bit all over the place, but the general gist is this: 30% of cats will obtain the virus, get sick with what is called the "primary viremia" stage of the disease, and mount a sufficient immune response so that they completely clear it and are immune for life. The rest of the 70% either die outright of infection (usually the kittens that are infected young before their immune systems are very good) or they become persistently infected with the "secondary viremia" stage of the disease because they didn't clear the virus. This stage occurs when the virus is present in the bone marrow and associated with white blood cells. These cats typically die within 1-3 years of suppressed immune system diseases like chronic respiratory infections, or lymphosarcoma.
Roosevelt's IFA was negative. This didn't fit with his history at all. There was no way Roosevelt could've been infected within the last year and a half as a single, indoor-only cat. The only way he could've been recently infected was if Cas or Mama had done so within the last couple of months, but both of them are negative. The reason this is odd is because a positive ELISA, which tests for the primary viremia stage, and a negative IFA, which tests for the secondary, white blood cell-associated stage, is only possible with recent infection. Which in Roosevelt's case was impossible.
With this confusing, discordant result, I submitted a PCR on whole blood. This test is the grand-daddy test that would determine if he had any circulating virus in his system at all. It was negative. That settled it; Roosevelt does not have FeLV. Curious, I took the second blood sample we drew for the PCR that I had saved part of, which was taken about a week later from the first sample I ran the first two ELISAs on, and ran a 3rd ELISA. It came back positive.
I've since spoken with two internal medicine specialists about this case - one of the phone consultant clinicians from Antech, the lab I submitted the tests to, and Dr. Gillespie who I externed with at IndyVet this past spring. Both feel that even with three positive ELISAs ran on two different blood samples taken on different days, this is a case of a false positive ELISA. Something in Roosevelt's blood is cross-reacting with the test as similar to the p27 protein FeLV antigen that the test screens for.
I submit this as a case for any of my vet school or fellow clinician readers. If you get a cat whose history does not fit with the clinical progression of FeLV, yet tests positive on ELISA, always submit a confirmatory test before euthanizing!