Infectious diseases are caused by microbes such as viruses, bacteria, protozoans, and fungi entering the body and attacking it. Microorganisms cause infections like chickenpox, meningitis, malaria, yellow fever, and more. Pathogens can be transmitted through touch, air, animals, contaminated food or water, or blood. Prevention methods include thoroughly cooking food, avoiding infected water, washing cuts and hands, not sharing drinks or utensils, and using protection during sex.