FIV affects a lot of the cats in the stray world as there are a lot of fights. The virus is spread by blood and saliva, so unfortunately a lot of tom cats are affected as they tend to fight a lot.
You can always tell when a cat has FIV. They don't look very good at all. They are very skinny, the quality of their coat is often very poor, they have chronic reoccurring infections, bad breath and many other symptoms.
There is a special blood test that can detect FIV. A drop of blood is taken from your cat and put in to a test strip, over about 10 mins the test will show whether you cats blood is positive or negative for FIV. Some cats don't show symptoms for up to 10 years but sadly FIV is eventually fatal. To protect your cat against the FIV you can vaccinate against the virus. Speak to your veterinarian about the right vaccination program for your cat.Lauren, Vet Nurse