Definitions

GERMS
   Germs are microorganisms, tiny living things that can only be seen with the help of a microscope. Billions of microorganisms live on your skin or in your body. Most of them are harmless; some actually help keep you healthy. Disease germs (which scientists call pathogens) are the exception. They are specific microorganisms which are capable of causing contagious diseases.
   Scientists have classified pathogens into six categories: viruses, bacteria, rickettsiae, fungi, protozoans and parasitic worms. Viruses and bacteria are the disease-causing agents of most childhood infections and the ones most relevant to primary grade school children.  

VIRUSES

   Viruses are smaller than any known cell. They are composed primarily of protein and nucleic acid, the genetic material responsible for determining the growth of cells in living organisms. Many of the viruses that have been identified are classified as pathogens, that is, capable of causing illness. Viruses can only multiply when they invade cells. Once inside a cell, a virus can cause disease by changing the normal chemical activity of the cell. The virus directs the cell to reproduce viruses. Once full of viruses, the cell bursts, spreading the new viruses to other cells where the process begins all over again. Viruses are responsible for more diseases than any other type of pathogen. Each different virus causes a specific disease.
   Examples include the common cold, influenza and most contagious childhood infections such as chicken pox, measles, mumps, cold sores and fever blisters. Scientists also suspect that viruses may be responsible for certain forms of cancer.  

BACTERIA

   Bacteria are single-celled organisms that have one of three basic shapes: rods (bacilli), round (cocci) or spiral (spirilla). Bacteria can grow and reproduce quickly by doubling in size and splitting in half. Bacteria can be found throughout the environment. You come into contact with them on almost everything you touch. Millions of bacteria are also normally present on and in the body. Most don’t cause problems and many help with the normal functioning of the body. For example, in the intestines, some bacteria help process body wastes for elimination. Other bacteria, however, are pathogenic. Pathogenic bacteria that live inside the body obtain food for the substance found in human tissue. They can cause disease when they produce specific products such as tetanus or other toxins that poison the body.
   Examples of diseases caused by bacteria include strep throat, pneumonia, diphtheria and tetanus. Pathogenic bacteria can also multiply in food that is improperly stored and can cause food poisoning.