Re: Moses tested FeLv+ and FeLv- I'm confused!

[Nina]

Hi Lee, First of all, thank you for helping this stray and caring enough, (and knowing enough), to not take the first test as definitive.  Your comment about the outhouse cracked me up.  I can relate, I'm out of space myself.  A while back we had a lively discussion about PCR testing for felv.  I asked at my specialty clinic and the paste below is the answer I received.  If you do a search in our archives, (search on pcr), you should come up with the entire discussion.  From what I recall, the problem with PCR testing is in the accuracy of the lab that is doing the work.  Here's one of my emails from the discussion: >Hi guys, I haven't had time to check my other emails and I late for a dog training appointment.  I did see this answer from Kate, chemist that used to work at my vet clinic.  Synchronistically, she is now doing research involving FelV and PCR testing!  I asked my vets the question I posed to Dr. Susan and this is the answer: This is Kate who used to work at VMSG.  I stopped by the office the other day, and asked about my old buddies.  Michelle told me Jazz and Gracie were doing well with the feline interferon treatment.  I'm so happy to hear that!!!! Anyway, I'm currently working at California Lutheran University, and I am getting to do research. Coincidentally enough I am working with FeLV (a strain that has not been sequenced yet) and am running PCR on it.  Okay, the difference between PCR and ELISA.... ELISA screens for antibodies (proteins) that are specific for the FeLV virus.  False positives may occur from other antibodies that mimic antibodies to the virus. Furthermore, kittens may show false positive, if the queen (momma cat) was exposed to FeLV, passing her antibodies along to her kitten, but not necessarily the virus.  ELISA shows that a cat has been exposed to FeLV, but not necessarily has the virus (this is why repeat testing must be done in order to determine that the cat is indeed positive for FeLV).  On the other hand, it is possible for a cat to be FeLV positive, but to have a negative ELISA.  For instance, if the virus is latent, ELISA may not show positive for the virus.  PCR (polymerase chain reaction), however, deals directly with the nucleic acid (the genteic material) of the virus, and amplifies it.  If the virus is not present, the genetic material of the virus is not present, and therefore, PCR will not make more of something that isn't there.  So, if a kitty has FeLV, it will be detectable by PCR.  A positive for PCR is 100% positive (provided the person running the sample did not contaminate it).  A negative PCR is almost always negative (provided the person running the PCR is experienced in the technique).  There are many studies out there that have used PCR to detect FeLV from bone marrow.  Therefore, a blood sample could be submitted to test for FeLV.  Ideally, the best would be to get a bone marrow sample.  Side note, red blood cells do not carry genetic material (they are the only cells that do not do this). Consequently, at a crime scene when the detectives obtain a blood sample they extract the genetic material from the white blood cells, and run a PCR. By running PCR they are able to take a small bit of genetic material and get it to generate alot of genetic material.  The genetic material in humans is of course DNA.  The FeLV virus's genetic material is RNA.  It is able to take it's RNA and make DNA (a process called reverse transcription, which only certain viruses can do), but it's DNA is short lived. Viruses cannot replicate on their own and require a host to carry out this process.  Short answer to your question is, yes, you can do a PCR test for FeLV.  Why this isn't used always instead of ELISA is a whole other  can of worms.  Basically, you have to separate kitty DNA from virus RNA, not hard but there can be contamination.  The genetic sequence of FeLV strain A is known, but researchers are not sure that this is the only strain that causes the virus, and whether other strains have an effect on the disease.  The primers (the little pieces of genetic material that tag the genetic material of the virus) have to be specific to make PCR work, i.e. to amplify the virus's genetic material.  Then there is a problem with standardization of tests from lab to lab.  PCR is an awesome tool, but alas, like everything else in the universe, comes with its own set of rules.  Basically, scientists do not have all the answers yet to FeLV. However, when we get results, these are published which allows doctors more information to treat thier patients.  But somewhere in a small lab, researchers continue to seek answers.....  Don't know if this helps or if you are more confused.>