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Pathogens are the bacteria and germs that cause the immune system to be weakened. They make us sick because out body sometimes cross paths with germy critters we aren't used to and our immune system isn't capable of fighting them. Hint some people have strong immune systems and get sick less compared to those who have a weak one. An Example would be when someone sneezes and the droplets from their sneeze spread in the air and come into contact with another person, also causing them to become sick. This is how pathogens spread through indirect and direct contact..