FIV is the cat equivalent of HIV in humans. Just as with human transmission of the virus, FIV can be passed through sexual contact but can also be transmitted through other bodily fluids. FIV has been shown to be a very species specific virus and has never been shown to convert to HIV.
FIV, as the name implies, is a virus that weakens the immune system to the point that the cat cannot effectively fight off even "simple" infections. Eventually, the cat can be classified as having an AIDS like syndrome much as humans with HIV eventually develop AIDS. Also like humans, there is no cure for this virus. Once it is contracted, the virus will persist for life.
Although there is a vaccination to help prevent contracting the virus, we have concerns about the efficacy. Once the vaccination is given, the cat will produce antibodies that will persist for life. The test necessary for diagnosing FIV looks for presence of antibodies and therefore will always test positive (false positive result).
Cats with FIV should be isolated from non-infected cats to help prevent spread of the disease. It has been shown that some cats may be more susceptible to the virus as well as some may be less susceptible to contracting FIV. Research is ongoing.
Cats with FIV should be aggressively treated for any infections or diseases. Infected cats can live for many years with this virus if monitored and treated appropriately.