This document discusses microorganisms and how diseases caused by them can spread. It covers the different types of microorganisms including bacteria, protozoa, fungi and viruses. While some microorganisms are helpful, others can cause illness when entering the body or contaminating food. Diseases can spread between people through various means such as sneezing, coughing, direct contact, insects, or through air/food/drink. Proper hygiene like hand washing and avoiding sharing personal items can help prevent the spread of diseases.