Pathogen
From Free net encyclopedia
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, "birth of pain."
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 contact/bite or ingestion. All of these mechanisms have different episodic time frames, but soil contamination has the longest or most persistent potential for harboring a pathogen.
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, 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 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. Plague is carried by fleas. 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). 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.
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.
| Pathogen | Examples | Typical effects |
|---|---|---|
| Bacteria | Escherichia coli | honeymoon cystitis or urinary tract infection (UTI), peritonitis, food poisoning |
| Mycobacterium tuberculosis | tuberculosis | |
| Salmonella | food poisoning | |
| Staphylococcus aureus | toxic shock syndrome | |
| Streptococcus pneumoniae | pneumonia | |
| Streptococcus pyogenes | strep throat | |
| Helicobacter pylori | Stomach ulcers | |
| Francisella tularensis | tularemia | |
| Viruses | Hepatitis A, B, C, D and E | liver disease |
| Influenza virus | flu | |
| Herpes simplex virus | herpes | |
| Molluscum contagiosum | rash | |
| HIV | AIDS | |
| Protozoa | Cryptosporidium | cryptosporidiosis |
| Giardia lamblia | giardiasis | |
| Plasmodium | malaria | |
| Trypanosoma cruzi | chagas disease | |
| Fungi | Pneumocystis jiroveci | opportunistic pneumonia |
| Tinea | ringworm | |
| Candida | candidiasis | |
| Parasites | Roundworm | |
| Scabies | ||
| Tapeworm | ||
| Flatworm | ||
| Proteins | Prions | BSE, vCJD |
Transmission of pathogens
See also
de:Krankheitserreger fr:Pathogène nl:Pathogeen pl:Patogen zh:病原 sv:Patogen tr:Patojen