You have many enemies, most not even thinking of damaging you, they just want a warm body of recourses to live in. But by doing that, they take away things that your cells need. Basic bacteria are weak, easily captured. At least, that is for weak, inexperienced bacteria that haven't gone through many mutations. But that is not much to talk about, so why don't we talk about the stronger ones?
...Just look in the diseases section, which is partially finished.