Earlier this year, The Veterinary Journal published an article about FIV-positive cats living with FIV-negative cats. Many, many people are afraid of adopting an FIV-positive cat because they don't want to infect their other cats. Shelters will also keep FIV-positive cats separate from fully healthy cats also (although that's for the protection of both groups). The study, conducted by Annette Litster of Purdue's College of Veterinary medicine, showed that FIV-positive cats don't transmit the disease to FIV-negative cats through normal interaction.
It's important to clarify "normal interaction." FIV, or feline immunodeficiency virus, is transmitted between cats when one cat bites another and breaks the skin. Cats living together can bicker enough to bite each other. According to the Cornell College of Veterinary Medicine, approximately 1.5 percent to 3 percent of cats in the U.S. have FIV, with the highest prevalence occurring in free-roaming male cats. They're the most likely to be aggressive, and thus, the most likely to give and receive serious bites.
FIV-positive cats may appear healthy and normal for years after contracting the virus. However, like other immune-deficiency conditions, the virus compromises the cat's immune system, which makes it harder for the cat to fight off even small infections. They might be so small that cats with healthy immune systems would never even show symptoms, but FIV-positive cats could get seriously ill.
According to Litster's work, most normal behavior between cats, including mutual grooming, won't transmit FIV at all. Cats also can't pick it up from the litter box, and Litster's study also showed indications that mothers don't pass FIV onto their kittens, either.
These are a couple of ways that FIV infection differs from infection with feline leukemia (FeLV). Cats can pass FeLV onto other cats through their saliva and their urine. So an uninfected cat could pick up FeLV in the litter box, from food and water bowls, and through mutual grooming, as well as through bickering. Cats can't pick up FIV those same ways.
Litster's study shows promise, especially for all the FIV-positive cats in shelters and rescues. However, it's necessary to introduce an FIV-positive cat into your household very slowly, and work to cultivate positive relationships between your cats so they don't bite each other. If you have cats that to tend to show aggression, it's better not to bring an FIV-positive cat into your house. You'll also want to be certain that any FIV-positive cat you do consider adopting also doesn't show aggressive tendencies towards other cats.