Some microorganisms harm us in various ways. Many organisms cause diseases. Disease causing microorganisms are called pathogens. Ailments like cold, influenza (flu) and most coughs are caused by viruses and even foot and mouth disease of cattle is also caused to virus. Serious diseases like, chicken pox and polio are also caused by viruses. Diseases like dysentery and malaria are caused by protozoan. Some bacteria cause typhoid and tuberculosis (TB) anthrax, a dangerous human and cattle disease, is also caused by a bacteria. Some microorganisms spoil leather items and wooden-work. Apart from these harmful effects, some microorganisms release toxic substances when grow on food items. Thus we see that microorganisms harm us in many ways.