What are pathogens and how do they cause disease?

Pathogens are microorganisms that can cause disease. Pathogenic bacteria make us ill in 2 way: 1) by damaging body cells 2) releasing toxins. Pathogenic viruses invade body cells where they use the cellular machinery to replicate. The call then bursts and the viruses go on to infect other cells. It is this bursting of cells that makes us ill when we are infected with viruses.