This article is from the Feline Leukemia (Cats) FAQ, posted to rec.pets.cats newsgroup. Maintained by Erin Miller with numerous contributions by others.
People often use the "it's like AIDS" phrase to describe a number of illnesses in the animal (and human) community with the idea that most people know so much about AIDS that this analogy is useful. Unfortunately most people don't know much about AIDS and the resulting effect is to scare people out of their wits and have them dump their cats or dogs at the nearest pound because they are so deathly afraid of AIDS. They are similar to AIDS in that they affect and weaken the body's immune system. The ONLY similarity between FeLV, FIV (Feline Immunodeficiency Virus) and FIP (Feline Infectious Peritonitis) is in their genetic makeup. All are RNA (as opposed to DNA) viruses, and FeLV and FIV are what are known as "retroviruses." FIP is a "coronavirus." (See the FIP FAQ for more information on this disease).