http://www.dhpe.org/infectintro.htm
Directors of Health Promotion and Education
Infectious diseases are human illnesses caused by viruses, bacteria, parasites, fungi, and other microbes. They may be spread by direct contact with an infected person or animal, by ingesting contaminated food or water, by insects like mosquitoes or ticks (disease vectors), or by contact with contaminated surroundings like animal droppings or even contaminated air. This fact sheet provides general facts about infectious disease, including reasons why infectious diseases emerge and reemerge, good news about infectious disease control, and infectious diseases’ agents and modes of transmission.