Some microbes, often called germs, cause illness or disease. They are parasites which live by invading living things. Chickenpox, mumps, and measles are all caused by viruses. Some bacteria are also germs. They cause many infectious diseases including tuberculosis and tetanus. Certain bacteria cause tooth decay. It is possible to protect humans against some harmful microbes by storing and preparing food properly, cleaning the teeth, washing hands, and by avoiding close contact with ill people. 