Viral Diversity Flashcards
What are segmented viruses
Viruses with genomes that are segmented into multiple separate RNA or DNA molecules, each usually encoding a different protein
What are non-segmented viruses?
Viruses with a single, continuous DNA/RNA molecule comprising their entire genome (one long strand of code, not separate packages)
What type of viruses undergo reassortment?
Segmented viruses
What is reassortment?
When two related segmented viruses infect the same cell and exchange genome segments during packaging
What are some examples of viruses that undergo viral reassortment?
Common in segmented RNA viruses like:
- Influenza A
- Rotavirus
What are some features of viral reassortment?
- Leads to rapid, dramatic changes in viral genotype and phenotype
- Can create new viral strains with pandemic potential
What is an example of a pandemic that occurred due to reassortment?
Influenza A pandemics like “swine flu” pandemic (2009)
What caused the swine flu epidemic?
A triple reassortant of human, swine and avian influenza strains
What type of viruses undergo recombination?
Non-segmented viruses
What is viral recombination?
The exchange of genetic material between two similar viral genomes within a single, continuous RNA/DNA molecule
What is the prerequisite for viral recombination?
Requires co-infection of a host cell by related viruses
When can viral recombination occur?
Via:
- Template switching during replication
- Breakage and rejoining of DNA in DNA viruses
What is the outcome of viral recombination?
Can lead to gradual evolution and new phenotypes
What is the main difference between viral evolution of segmented vs non-segmented viruses?
Segmented viruses allow for reassortment, which enables evolutionary jumps (key factor in Influenza pandemics).
In contrasts, non-segmented viruses rely on mutation and recombination, leading to slower, stepwise change
What type of genomes does recombination produce?
Mosaic genomes- a more patchwork of genetic material from different viruses
What type of genomes does reassortment produce?
Chimeric genomes- often contain entire functional genes from other viruses
What are some examples of viruses that undergo recombination?
- Polioviruses
- Coronaviruses
What is the main cause of influenza pandemics?
Antigenic SHIFT
What is the main cause of seasonal epidemics?
Antigenic DRIFT
What is antigenic shift?
A sudden, major change in viral genome due to reassortment of genome segments
What is antigenic drift?
A process of gradual genetic change caused by the accumulation of point mutations
What viral types of Influenza are affected by each antigenic process?
Drift affects both Influenza A and B
Shift only affects Influenza A, as it infects multiple species (allowing for mixed infections)
What is the impact on the virus of each antigenic process?
Drift = minor antigenic variation in HA and NA - gradually reduces vaccine effectiveness
Shift = new viral subtypes with novel HA and/or NA combinations - no pre-existing immunity in population
What are two examples of Influenza pandemics?
2009 H1N1
1968 H3N2
