A pathogen (
- Pronunciation Guide to Microorganisms (1)
- Pronunciation Guide to Microorganisms (2)
- Dictionary.com: Pathogen. Retrieved August 17, 2013
- MetaPathogen - about various types of pathogenic organisms
- The prion diseases STANLEY B. PRUSINER, Scientific American
- Viral Special Pathogens Branch |  Moved | CDC
- Ecological competence
- Emerging Pathogens Institute
- Human pathogen
- List of human diseases associated with infectious pathogens
- Pathogen-Host Interaction Database (PHI-base)
Transmission of pathogens occurs through many different routes, including airborne, direct or indirect contact, sexual contact, through blood, breast milk, or other body fluids, and through the fecal-oral route.
Evolutionary medicine has found that under horizontal transmission, the host population might never develop tolerance to the pathogen.
Virulence (the tendency of a pathogen to cause damage to a host's fitness) evolves when that pathogen can spread from a diseased host, despite that host being very debilitated. Horizontal transmission occurs between hosts of the same species, in contrast to vertical transmission, which tends to evolve symbiosis (after a period of high morbidity and mortality in the population) by linking the pathogen's evolutionary success to the evolutionary success of the host organism.
Bacteria are usually treated with antibiotics while viruses are treated with antiviral compounds. Eukaryotic pathogens are typically not susceptible to antibiotics and thus need specific drugs. Infection with many pathogens can be prevented by immunization. A small amount of pathogens are used in vaccines to make immunity stay alert and strengthen defense on the insides to prepare for a larger quantity of the virus ever getting inside. Hygiene is critical for the prevention of infection by pathogens.
Treatment and health care
Fungi comprise a eukaryotic kingdom of microbes that are usually saprophytes (consume dead organisms) but can cause diseases in humans, animals and plants. Fungi are the most common cause of diseases in crops and other plants. The typical fungal spore size is 1-40 micrometers in length.
Although the vast majority of bacteria are harmless or beneficial, a few pathogenic bacteria can cause infectious diseases. Bacteria can often be killed by antibiotics because the cell wall on the outside is destroyed, expelling the DNA out of the body of the pathogen, therefore making the pathogen incapable of producing proteins and dies. They typically range between 1 and 5 micrometers in length.
Pathogenic viruses are diseases mainly those of the families of: Adenoviridae, Picornaviridae, Herpesviridae, Hepadnaviridae, Flaviviridae, Retroviridae, Orthomyxoviridae, Paramyxoviridae, Papovaviridae, Polyomavirus, Rhabdoviridae, Togaviridae. Viruses typically range between 20-300 nanometers in length. 
According to the prion theory, prions are infectious pathogens that do not contain nucleic acids. These abnormally folded proteins are found characteristically in some diseases such as scrapie, bovine spongiform encephalopathy (mad cow disease) and Creutzfeldt–Jakob disease. Although prions fail to meet the requirements laid out by Koch's postulates, the hypothesis of prions as a new class of pathogen led Stanley B. Prusiner to receive the Nobel Prize in Physiology or Medicine in 1997.
Subcellular infectious objects
Types of pathogen
Types of pathogen 1
Subcellular infectious objects 1.1
- Prionic 1.1.1
- Viral 1.1.2
- Bacterial 1.2.1
- Fungal 1.3.1
- Other parasites 1.4
- Subcellular infectious objects 1.1
- Treatment and health care 2
- Virulence 3
- Transmission 4
- See also 5
- References 6
- External links 7
Not all pathogens are necessarily undesirable to humans. In pest populations.
There are several substrates including pathways whereby pathogens can invade a host. The principal pathways have different episodic time frames, but smallpox, influenza, mumps, measles, chickenpox, ebola and rubella.