Feline distemper, or panleukopenia, is a highly infectious respiratory disease. This virus attacks the immune system, hitting the lymph nodes first and then attacking bone marrow, affecting the patient's ability to produce white blood cells and recover.

Kittens are typically vaccinated against this highly communicable disease at ages 8, 12, and 16 weeks. Adult cats, especially those that may be in kept in groups, are typically vaccinated yearly.