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Encyclopedia > Pathogens

A pathogen (literally "birth of pain" from the Greek παθογένεια) is a biological agent that can cause disease to its host. A synonym of pathogen is "infectious agent". The term "pathogen" 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 (see Viruses, below).

Contents

Overview

The human body has many natural defenses against some of the more 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 or HIV, or by antibiotics being taken to kill other pathogens,) pathogenic bacteria that was being held at bay can proliferate and cause harm to the host. Such cases are called opportunistic infections.


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 life on Earth, and can be particularly devastating to its human inhabitants.


Threat of pathogens

Some pathogens (such as Yersinia pestis, which caused the Black Plague, and the aforementioned Variola virus) have been found responsible for massive amounts of casualties and have had numerous effects on afflicted groups. Of particular note in modern times is HIV/AIDS, which is known to have infected several million humans globally, threatening entire populations in certain parts of the world, as well as the recently emerged Severe Acute Respiratory Syndrome, or SARS.


Notable 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.


Bacteria

Viruses

Protozoa=

Fungi

Parasites

See also


  Results from FactBites:
 
Pathogen - Wikipedia, the free encyclopedia (366 words)
A pathogen or infectious agent is a biological agent that causes disease or illness to its host.
There are several substrates and pathways whereby pathogens can invade a host; the principal pathways are: air contact/respiration; water contact/ingestion or dermal contact; soil contact/dermal or ingestion; and animal(vectors) contact/bite or ingestion.
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.
  More results at FactBites »

 
 

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