Human DiseaseDifferent agents, or microorganisms, cause disease; thus, they are often referred to as infectious agents. Collectively these agents are called pathogens. There are five types of disease agents
Pathogens can enter a host through a variety of ways commonly called modes of transmission. One mode of transmission is direct contact with an infected person or animal, such as a bite from an infected animal. Some diseases are spread by vectors, which are intermediaries that carry the agent from a reservoir to a host; insects, such as mosquitos, often are vectors. Some pathogens are airborne meaning the microorganism is suspended in the air. Some pathogens are too small to be seen with the unaided, or naked, eye. The next page illustrates the size of some pathogens relative to more familiar items. |
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