Sometimes, even with proper preventative care, kitty can become ill. Here are some articles with information.

Feline Upper Respiratory Illness - From Mar Vista Animal Medical Center

Feline Leukemia Virus (FeLV) - From Cornell Veterinary Medicine

Feline Immunodeficiency Virus (FIV) - From Cornell Veterinary Medicine

Preventative medicine information:

Information on feline vaccinations - From Pawprints and Purrs

Schedule for feline vaccinations - From University Animal Hospital, New York