Virus Mutation

• A viral mutation is any change in the sequence of Nitrogen bases of DNA or RNA in a viral genome
• The changes can also take place at the level of mRNA during editing or at the protein during translation
• These changes helps some virus to adapt to new hosts and environments
• Mutation rates of virus genomes are determined by nucleic acids
  -RNA viruses have higher mutation rates (10-3 to 10-5)
  -DNA viruses have lower mutation rates (10-6 to 10-8)
  -Single-stranded viruses mutate faster than double-strand virus
• Viral DNA/RNA polymerases are not equipped with proofreading capability (have poor proof reading)
• Eukaryotic organisms have lower mutation rates (10-6 to 10-8) compared to viruses due to high proofreading capability (10-6)

Origin of mutants

Spontaneous mutations: Arise naturally during viral replication due to errors by the genome-replicating polymerase or as a result of the incorporation of  tautomeric forms of the bases

Mutations that are induced by physical means: Arise as a result of exposure to agents such as UV light or X-rays

Mutations that are induced by chemical means: As a result of agents acting;

• directly on bases, e.g. nitrous acid or
• indirectly, e.g. base analogs that mispair

Types of viral mutation

• Point Mutations (Single nucleotide replacement)
• Insertion/deletion of nucleotides
• Frameshift mutation
• Inversion
• Recombination and Reassortment

a) Classic Recombination (breaking and joining)

b) Copy choice recombination

c) Reassortment

• Phenotypic mixing