[From Tufts March 2011 Issue]
For the last several years, we have been feeding a feral cat. About six months ago, we were successfully able to trap him and brought him to a veterinary clinic to be neutered and vaccinated. Unfortunately, he tested positive for feline immunodeficiency virus (FIV).
Since then, he has become much more mellow, coming when we call him and allowing us to pet him when he is eating. We created an outdoor shelter for him that includes a heated water bowl and heated cat beds. Twice a day, he is fed a quality high-protein diet, and monthly, he receives a topical flea treatment. Separated by a screen door, he interacts nicely with our three indoor cats who are all FIV-negative.
We know that FIV-positive and FIV-negative cats can coexist with virtually no risk of transmission of the disease, but because he was born feral, it concerns us that a fight with a serious bite wound occurring can’t be completely ruled out as a possibility if he was allowed to live indoors. Would it be too risky to have him as a permanent indoor cat with our FIV-negative cats? And if so, would vaccinating our indoor cats against FIV make sense?
Dear Crystal: Cats acquire the infection by being bitten by another cat that is infected with the virus. Free-roaming, non-neutered male cats are at higher risk due to their territoriality and increased propensity for fighting. Your questions have no clear-cut answer. As you noted, because FIV is spread mainly through biting, cats living in households with an FIV-positive cat may be at lower risk for FIV infection if a stable social structure exists and fighting does not occur. However, there have been rare reports of transmission between cats who live peaceably in close proximity over a long period of time. Given this situation, whether or not to vaccinate should be discussed with your veterinarian.
If the decision falls in favor of vaccination, cats should be tested and be negative immediately prior to vaccination. Vaccination of cats who are already infected, while not harmful, confers no benefit. Cats who are vaccinated against FIV will subsequently test positive for FIV antibodies. A test has been developed that can distinguish whether FIV antibodies are the result of infection versus vaccination, although this test is not available in the United States.
I think you should add this sweet cat to your household, and that you should vaccinate the other cats in the house. If one of your cats does get sick in the future, you won’t be able to determine whether the illness is due to your cat being truly FIV positive versus just testing positive due to vaccination (unless the test becomes available by that time in the U.S.).
Arnold Plotnick, DVM
Catnip Medical Editor