To "fight disease" means taking actions and making efforts to prevent, cure, or combat an illness or health condition in order to keep people healthy and safe. Full definition
It's the science that explains how medicines work and are processed by the body — crucial for discovering new medicines to help fight diseases such as cancer, depression and heart disease. (politics.co.uk)
The use of radiation has not been proven to be useful in fighting this disease at this time. (caninecancer.com)
Sleep is vital for relieving the body from inflammation, stress, and for fighting disease. (heathermcclees.com)