Newton’s Purrspective – The Texas “Miracle Cats”
Feline Leukemia Virus (FeLV) is the most common cause of cancer in cats. It can also lead to a variety of blood disorders and/or immune deficiency. FeLV is transmitted through bodily fluids and kittens may even be infected in utero. Although a vaccine is available it is not 100% effective and there is no known cure. http://www.vet.cornell.edu/fhc/health_information/brochure_felv.cfm
FeLV positive cats are routinely euthanized in most shelters. A small number of shelters provide separate housing, keeping them forever, or only adopt them out to homes without other cats. I recently watched the video about “the ‘miracle’ cats at Shadow Cats in Round Rock, Texas. No one knows how or why, but after years of living under the cloud of the Feline Leukemia Virus, they’ve managed to clear the deadly virus from their bodies.” https://vimeo.com/120023750
How could this happen?
According to the video 10 cats who had tested positive for FeLV were negative when retested later. This is almost 50% of their usual FeLV positive population. Exact time frames and type of test used are not given, so I have to make some educated guesses regarding what happened.
There are two stages of the disease:
- Primary viremia – during this stage some cats can effectively fight off the disease and eliminate the virus
- Secondary viremia – at this point the virus is in the bone marrow and cannot be eliminated
There are two types of blood tests used to diagnose FeLV:
- ELISA (enzyme-linked immunosorbent assay) performed on site
- IFA (indirect immunofluorescent antibody assay) sent out to a diagnostic laboratory
ELISA detects both primary and secondary viremia, but cannot differentiate between the two. IFA detects only the secondary stage.
If the ELISA was positive on a pet cat a blood sample would be sent for IFA to provide an accurate diagnosis. However, shelters typically use only the cheaper in house tests. A positive test means the cat will be euthanized or housed solely with other FeLV positive cats.
So what happened at the Shadow Cats shelter?
- ELISA can give false positive results so some of the cats might never have had FeLV.
- Some of the cats may have had only primary viremia.
- Although reversal of primary viremia is not common, it can occur.
IMPORTANT! I do need to clarify something. The narrator used the term “shed” several times when describing cats who no longer tested positive. He does not understand and is misusing an important medical term. Not understanding what “shed” or “shedding” really means could have fatal consequences.
Shedding means that the cat is releasing the virus – much like that period of time when one human is contagious and can transmit a nasty cold to another human. When a cat is shedding a virus this is a period of time when the virus would likely infect other cats in the environment. What he should have said is that the cats no longer had the virus in their bodies so they were not carriers any longer. This is why it was safe to move them out of the isolation area.
I do wonder what prompted them to retest the first FeLV positive cat. Prior to the surprising negative result they had no protocol for retesting. The cats in the video certainly looked healthy and well cared for. Their environment appeared to have minimal stress – something that is critical both for preventing and for curing disease.
So, here is what I think.
- Either the miracle cats never had FeLV, or they had the stage that is reversible.
- A nurturing environment helped the FeLV positive cats to fight off the disease while it was still in the early stage.
- It certainly makes a case for retesting FeLV positive cats, both after the initial positive results (to rule out false positives), and after being housed away from non-infected cats for some time (to see if cats in the primary stage had fought off the virus successfully).