Feline Immunodeficiency Virus (FIV): A retrovirus that enters the lymph nodes and targets the white blood cells that fight infection. As a result, the cat is unable to fight off various infections and cancers.
Feline Infectious Peritonitis (FIP): A hard to diagnose, fatal, and not typical disease. In attempt to fight against this virus, your cat's immune system actually speeds along the process of the disease. It can often be difficult to diagnose because each cat can display signs similar to many other diseases.
Feline Panleukopenia (Feline Distemper): A severe, highly contagious, viral disease. This virus tends to invade cells which are rapidly growing.