General Studies III

Mutation of Virus

Mutation of Virus
  • Mutation, an alteration in the genetic material (the genome) of a cell of a living organism or of a virus that is more or less permanent and that can be transmitted to the cell’s or the virus’s descendants.
  • Like all life, viruses carry a genetic code in the form of nucleic acids — either DNA or RNA.
  • When cells multiply, the DNA within them replicates as well, to make copies for the new cells.
  • During replication, random errors are introduced into the new DNA, much like spelling errors when we write.
  • While the errors in DNA virus genomes can be corrected by the error-correcting function of cells in which they replicate, there are no enzymes in cells to correct RNA errors.
  • Therefore, RNA viruses accumulate more genetic changes (mutations) than DNA viruses.
Effect of mutation on the virus
  • Evolution requires not just mutations, but also selection.
  • While most mutations are deleterious to the virus, if some allow a selective advantage — say better infectivity, transmission, or escape from immunity — then the new viruses out-compete the older ones in a population.
  • The mutations can be synonymous (silent) or non-synonymous (non-silent); the latter also changes an amino acid (protein building block) at that position in the coded protein.
Why is it harmful?
  • Viruses with mutations within the receptor-binding domain (RBD) of the Spike protein have the most potential to evade antibodies that develop as a result of natural infection or vaccination.
  • The RBD binds the cellular receptor allowing the virus to infect cells, and anti-RBD antibodies neutralize the virus.
  • Such mutations were recently found in variant viruses that emerged in the UK, South Africa and Brazil.
Testing of mutation
  • Indirect tests are done in laboratories to assess if an emerging variant might escape antibodies developed after natural infection or vaccination.
  • Serum (the blood components that contain antibodies) from recovered patients or vaccinated people, and antibodies are known to neutralize the original virus, are tested.
  • Serial dilutions of the serum or antibodies are separately mixed with a fixed amount of the original and variant viruses, and the mixture is added to cells in culture.
  • After a period of incubation, cells are washed and stained. Cells infected and killed by viruses multiplying within them appear as clear zones (plaques) on a dark background.
  • The effectiveness of serum or antibody is expressed as an inhibitory concentration (IC) or plaque reduction neutralisation titer (PRNT) value.

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