Viral genetics and emerging viruses Flashcards
What are the ways in which genetic change can occur in viruses?
Spontaneous mutation and genetic exchange between viruses (and with cells)
What is a mutation?
A change in the nucleotide sequence of a genome due to an error in copying the parental template
How can genetic material be exchanged between 2 viruses?
Recombination and reassortment
Describe ‘spontaneous mutation’
Occurs during replication. Can be a point mutation (more likely in RNA), insertion, deletion or rearrangement
What are the possible consequences of spontaneous mutation?
Potential alteration, loss of protein structure and function, altered levels of expression. Often lethal
Define ‘quasispecies’
A group of viruses related by a similar mutation/s, competing within a highly mutagenic environment
Describe recombination
Related (homogolous) sequences on 2 different virus genomes switch. Homogolous recombination. Can also occur between cells and viral genome sequences
Describe reassortment
- 2 viruses infect the same cell
- One or more genes is transfered between the 2 viral genomes to create a novel combination
* occurs in segmented RNA viruses*
What are the consequences to viruses of recombination?
Lethal mutation, silent mutation, persistant damage, persistant advantage
What are the properties of an influenza virus?
Important envelope glycoproteins - H, N
Genome consists of 8 linear RNA segments
Enveloped
What does ‘H’ stand for?
Haemagglutinin - major antigen for neutralising antibodies. Binds to host receptors
What does ‘N’ stand for?
Neuraminidase - releases progeny of the virus from the cell surface
How can changes to H and N occur?
Antigenic drift and antigenic shift
Describe influenza infection in birds
Affects alimentary tract in wild aquatic birds
Largely asymptomatic
Transmitted by faecal/oral route
All H and N types
In which species is influenza most prominent?
Horses, dogs, pigs and humans
How many H and N variants are there?
H - 16
N-9
Define ‘antigenic drift’
Gradual accumulation of minor antigenic changes in surface proteins over time.
Define ‘antigenic shift’
Exchange of whole genome segments between 2 influenza viruses, potentially causing a major antigen change
How are influenza virons activated to cause disease?
LPAI - Single AA base is cleaved by host proteases in resp and GI tracts, causing resp infection
HPAI - Multiple AA bases are cleaved by host proteases in resp and GI tracts and other tissues causing sytemic infection
What are the public health implications of viruses?
Viruses are dynamic, meaning new diseases are constantly emerging
Define ‘emerging/re-emerging disease’
pathogen that is newly recognised or newly evolved, or that has occurred previously but shows an increase in incidence or expansion in geographical, host or vector range
Define ‘epidemic’
Spread of disease to many individual
Define ‘pandemic’
Spread of disease on a global scale
How are new diseases emerging in animals and humans?
- Change in mans interaction with the environment and alteration of it
- Changing dynamic of animal/human populations
- Climate effects (e.g. shifting insect populations)
- Capacity of viruses to change
How can zoonotic viruses emerge from a wildlife reservoir?
- Interspecies contact
- Cros-species virus transmission
- Sustained transmission in new species
- Virus adaptation to new species
How can influenza be controlled?
Vaccination Antiviral drugs Isolation of patients Education Hygiene strategies Surveillance Development of new vaccines
