FIV is transmitted through exchange of saliva during a deep, penetrating bites. It can be gotten through a blood transfusion. And if I am correct, also when cats mate.

Cats should be tested to see if they have the FIV virus in their systems. Because as I have been reading, clinical signs usually don't surface until late in the progression of the disease.

FIV is just a virus that supresses the immune system.....which means that cat cannot fight off infection as well as a NON- FIV+ cat.