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When do genetic changes in a virus occur?
During viral replication
What is the difference between genetic stability and genetic variation?
Genetic stability is the maintenance of a virus genome from generation to generation. Whereas genetic variation is the emergence of new viral strains with new biological properties as a result of mutation and selection.
Mutation is a change in the nucleotide sequence of a genome
Give examples of mutations that involve only one nucleotide. What term is used to describe these types of mutations?
- Insertion, deletion
- Point mutations
Spontaneous mutation is much higher in RNA/DNA viruses? Why?
It is much higher in RNA viruses as they need to encode their own polymerases which are not as good at recognising mistakes in their cellular replication as DNA polymerases.
What are quasispecies?
A collection of very closely related sequences in a viral population
Two viruses have very closely related viral genomes. Part of the genome of the two viruses is swapped. This affects a few proteins rather than a few bases.
What type of viruses can take place in reassortment?
Segmented RNA viruses
If two segmented viruses co-infect a cell the genome can mix with each other. Each segment codes for one or more proteins so reassortment can cause a change in the output proteins of the virus.
Define an a) lethal b) silent mutation
- a) A mutation that leads to the death of the virus
- b) A change at a genetic level but not a phenotypic level
What must be present to favour the establishment of new viral strains?
Is the influenza A virus a segmented/unsegmented DNA/RNA virus?
A segmented RNA virus
How many segments are present in the influenza A virus?
8 linear segments
What are the two types of envelope glycoproteins present on influenza A virus?
Haemagluttinin (H) and Neuraminidase (N)
What is are the functions of H and N?
- H - major antigen for neutralising antibodies, binds to host receptors
- N - release of progeny virus from cell surface
What is the difference between antigenic drift and antigenic shift?
Antigenic drift is spontaneous mutations in surface antigens which leads to the selection of variants in a partially immune population. Whereas antigenic shift is a major change in surface antigenicity associated with reassortment (or recombination).
Which species is responsible for the wild reservoir of influenza A virus?
Wild aquatic birds
Which other species can become infected with influenza A virus?
Humans, pigs, horses and dogs
Which is responsible for seasonal flu/pandemic flu? Antigenic drift or antigenic shift?
- Seasonal flu is caused by antigenic drift (minor changes in surface proteins)
- Pandemic flu is caused by antigenic shift - this results in the emergence of strains with new antigenic type to which the population has no prior immunity.
Which species is commonly referred to as a 'mixing pot' for influenza A virus?
Pigs, as they can be easily infected by human, avian and swine influenza so are a good place for new strains to be created.
True or false: vaccines do not need to be updated?
False: vaccines must be modified periodically to reflect currently circulating strains.
From what species did canine influenza spread to and from in the US?
It spread from horses to dogs
What does LPAI and HPAI stand for?
Low pathogenicity avian influenza and High pathogenicity avian influenza
What type of mutation is required to make influenza infectious?
To be infectious influenza virons require cleavage of the HA precursor.
What is the difference in this mutation in LPAI vs HPAI?
In LPAI this mutation only affects a single basic amino acid whereas in HPAI the mutation affects multiple basic amino acids
What is an emerging/re-emerging disease?
A pathogen that is newly recognised or newly evolved, or that has occurred previously but shows and increase in incidence or expansion in geographical, host or vector range
What is an epidemic/pandemic disease?
- Epidemic - spread of disease to many people
- Pandemic - an epidemic occurring worldwide
What is a zoonotic disease?
One that can be transferred between man and other animals
List some sources of infection by viruses
- Direct contact with animal/avian species
How can we control avian influenza?
- Vaccinate with up to date vaccines
- Antiviral drugs
- 'Barrier', education and hygiene strategies
- Eradication of infected birds
- Development of new vaccines
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