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Pathogen
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A pathogen or infectious agent is a biological agent that causes disease or illness to its host. The term is most often used for agents that disrupt the normal physiology of a multicellular animal or plant. However, pathogens can infect unicellular organisms from all of the biological kingdoms. The term pathogen is derived from the Greek παθογένεια, "that which produces suffering."
There are several substrates and pathways where by pathogens can invade a host; the principal pathways have different episodic time frames, but soil contamination has the longest or most persistent potential for harboring a pathogen.
The human body contains many natural defenses against some of the common pathogens (such as Pneumocystis) in the form of the human immune system and by some "helpful" bacteria present in the human body's normal flora. However, if the immune system or "good" bacteria is damaged in any way (such as by chemotherapy, human immunodeficiency virus (HIV), or antibiotics being taken to kill other pathogens), pathogenic bacteria that were being held at bay can proliferate and cause harm to the host. Such cases are called opportunistic infections.
Some pathogens (such as the bacterium
Yersinia pestis, which may have caused the
Black Plague, and the
Variola virus) have been found to be responsible for massive amounts of casualties and have had numerous effects on afflicted groups. Of particular note in modern times is HIV, which is known to have infected several million humans globally, as well as
Severe Acute Respiratory Syndrome
(SARS) and the
Influenza virus. Today, while many medical advances have been made to safeguard against infection by pathogens, through the use of
vaccination,
antibiotics, and
fungicide, pathogens continue to threaten human life. Social advances such as
food safety,
hygiene, and
water treatment have reduced the threat from some pathogens.
Contents
- 1 Types of pathogens
- 2 Transmission of pathogens
- 3 Transmission to vascular plants
- 4 See also
- 5 External links
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Types of pathogens
Below is a listing of different types of notable pathogens as categorized by their structural characteristics, and some of their known effects on infected hosts.
Transmission of pathogens
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One of the primary pathways by which food or water become contaminated is from the release of untreated sewage into a drinking water supply or onto cropland, with the result that people who eat or drink contaminated sources become infected. In developing countries most sewage is discharged into the environment or on cropland as of 2006; even in developed countries there are periodic system failures resulting in a sanitary sewer overflow. This is the typical mode of transmission for the infectious agents of (at least):
Transmission to vascular plants
In the case of terrestrial
vascular plants, pathogenic infection can occur by contact with foliage, and also from root uptake of soil pathogens. The latter pathway explains why some plant families such as
orchids are more disease resistant, since they rely upon
fungal hyphae to supply
nutrients rather than root structures, which have larger radii for conveying certain pathogens.
See also
