Pathogen persistence

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In infectious diseases, pathogen persistence refers to the persistence of pathogens in certain areas of retreat in the host's body through immune evasion , even after a possible infectious disease has healed . The pathogen persistence can arise through the transition of the pathogen into dormant, non-reproducing permanent forms or through constant multiplication of the pathogen in the sense of a chronic infection. The latter can lead to permanent elimination of the virus, leading to the spread of pathogens in the epidemiologically important chronic carriers leads. Not every infected individual has to become a permanent excretor, it is often only a small percentage. This is the case, for example, in bacterial infections with salmonella in humans and chickens or viral infections with the bovine viral diarrhea virus in cattle.

The persistence of the pathogen through dormant permanent forms is also referred to as latent infection (see lysogenic cycle ), which under certain circumstances (e.g. immunosuppression ) can lead to an increase and thus to another episode of the disease; this is also known as reactivation. The permanent forms can exist as metabolically inactive forms (example Mycobacterium tuberculosis in the so-called encapsulated tuberculosis ) or in the case of some viruses as persistence of the genetic information in individual cells. The hepatitis B virus can remain in the cell nucleus as cccDNA or all members of the Herpesviridae as episomes . In retroviruses such as HIV , the pathogen DNA can be integrated into the cell's genetic material. In addition to the dormant forms of the pathogens, there are also cell types with immune privilege in which not all mechanisms of the immune system are available (e.g. neurons ). Constantly emerging escape mutations lead to an avoidance of an effective adaptive immune response in HIV and HCV.

The ability of a pathogen to remain in a host and not be eliminated by the immune system requires highly specific adaptations and control mechanisms. However, once persistence with permanent or recurring excretion has been achieved, the pathogen has a considerable selection advantage , since a large number of hosts can be infected over a longer period and the pathogen can circulate in a population over a long period of time .

literature

  • C. Mims, HM Dockrell et al .: Medical microbiology / infectiology . Elsevier, Munich 2006, ISBN 3-437-41272-8 .
  • S. Modrow, D. Falke, U. Truyen: Molecular Virology. 2nd edition, Spektrum, Heidelberg 2003, ISBN 3-8274-1086-X .
  • DM Knipe, Peter M. Howley , DE Griffin, (Eds.): Fields Virology. 5th edition, Lippincott Williams & Wilkins, Philadelphia 2007, ISBN 978-0-7817-6060-7 .