Emergent Virus

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As Emergent virus (English for "(new) arising virus," often in the plural as Emerging Viruses ) one is the virus then referred to when it is in a population of newly occurring organisms or its spread in the population unusually rapidly and with high incidence happens. This can occur through an adaptation of a virus to a new host as a cross-species host change or through the emergence of a new, more pathogenic virus variant within the previous host species. The term emerging viruses (in German sometimes translated as new emerging viruses ) is a special form of the emerging pathogen (or emerging disease ), which also includes bacterial , prokaryotic and other parasitic pathogens .

In epidemiology, viruses are also referred to as emerging viruses that have been present in a population for a long time, i.e. have not reappeared, but a change in the transmission rate due to environmental influences, an increase in population density or changes in the vector population have become epidemiologically important pathogens worldwide.

Origin of emerging viruses

A prerequisite for a newly emerging virus is the transition from a previous host to a new host species and circulation within the new host population (English viral traffic ). For the first condition, the virus needs a high variability on its surface, since the virus must be able to dock on different receptors on the cell surface in the new host. One speaks of a low tropism of these viruses. Therefore, host transition between similar host species (e.g., between primate species , between mammals, or between rodents ) is often easier than between phylogenetically distant species. The transition is facilitated by close contact between the old and the new host, for example by pets or farm animals on humans or by penetration of humans into new ecosystems with their own host-virus relationships. Viruses with high genetic variability have a particularly high potential to penetrate new host species. Genetically, RNA viruses can mutate faster than DNA viruses and viruses with a viral envelope have more possibilities to change their surface than non-enveloped viruses, since the latter mutations can also lead to instability of the capsid and the virion disintegrates or can no longer be assembled can. For these reasons, almost all important emerging viruses in animals and humans are enveloped RNA viruses ( Filoviridae , Coronaviridae , flaviviruses , Togaviridae ). The genetic variability can be accelerated by a reassortment if the enveloped RNA viruses additionally have segmented genomes, which allow the segments from different virus strains or subtypes to be rearranged ( Bunyaviridae , Orthomyxoviridae such as the influenza viruses). These properties can be found in arboviruses , i.e. viruses that are transmitted as vectors by ticks or mosquitoes and have a low tropism due to the change between reservoir host and vector.

The second condition of “viral traffic” is favored when the population density of the new hosts is high . As a result of the circulation in the new host, the virus adapts to the new host, so that its contagiousness (usually initially low) increases and the virus can establish itself in the new population. Viruses newly entering a population usually have a high pathogenicity and sometimes also a high lethality . Frequent reservoir hosts for emerging viruses are birds and rodents, especially other primates and bats in humans .

In the history of mankind, emerging viruses have occurred repeatedly and very likely regularly. In small nomadic groups as hunters and gatherers without a permanent coexistence with farm animals, the chance of new viruses becoming established was less than after humans settled down and cattle breeding began in the Neolithic Revolution . The close contact with farm animals (cattle, sheep, goats and pigs) and the increase in human communities in settlements has very likely led to the establishment of important virus infections in humans. The increase in human population density due to urbanization in the High Middle Ages led to a further intensification of this transition. It is assumed that the measles virus emerged as an emergent virus from the rinderpest virus during this period .

Important emerging viruses

Emerging Viruses in Humans
Emerging Viruses in Animals
Emerging Viruses in Plants

Re-emerging virus

A re-emerge or re-emerging virus is used when the virus in its present form has been known for a long time, but changes in the virus ecology (again) trigger large epidemics or the area of ​​distribution of the virus infection changes. This can be done, for example, by changing the vector or importing the virus into a new ecosystem with suitable vectors and hosts. Examples of re-emerging viruses are the Zika virus with its occurrence in South America or the Usutu virus in European bird populations.

literature

  • Stephen S. Morse (ed.): Emerging Viruses . Oxford University Press 1993, ISBN 0-19-507444-0 .
  • S. Bedhomme et al .: Emerging viruses: why they are not jacks of all trades? Curr. Opin. Virol. (2015) 10: pp. 1-6 PMID 25467278 .
  • JS Mackenzie, M. Jeggo: Reservoirs and vectors of emerging viruses . Curr. Opin. Virol. (2013) 3 (2): pp. 170-179 PMID 23491947 .
  • EC Holmes: What can we predict about viral evolution and emergence? Curr. Opin. Virol. (2013) 3 (2): pp. 180-184 PMID 23273851 .
  • A. Zeltina et al .: Emerging Paramyxoviruses: Receptor Tropism and Zoonotic Potential. PLoS Pathog. (2016) 12 (2) doi : 10.1371 / journal.ppat.1005390

Individual evidence

  1. ↑ Y. Furuse et al .: Origin of measles virus: divergence from rinderpest virus between the 11th and 12th centuries. Virology Journal (2010) 7 (4): 52 PMID 20202190
  2. ^ B. Choudhury: From the field to the lab-an European view on the global spread of PEDV . Virus Research (2016) doi : 10.1016 / j.virusres.2016.09.003 PMID 27637348
  3. ^ RR Martin et al .: New and emerging viruses of blueberry and cranberry. Viruses (2012) 4 (11): pp. 2831-2852 PMID 23202507