Viral genetics and emerging viruses

Question 1

What are the ways in which genetic change can occur in viruses?

Answer 1

Spontaneous mutation and genetic exchange between viruses (and with cells)

Question 2

What is a mutation?

Answer 2

A change in the nucleotide sequence of a genome due to an error in copying the parental template

Question 3

How can genetic material be exchanged between 2 viruses?

Answer 3

Recombination and reassortment

Question 4

Describe ‘spontaneous mutation’

Answer 4

Occurs during replication. Can be a point mutation (more likely in RNA), insertion, deletion or rearrangement

Question 5

What are the possible consequences of spontaneous mutation?

Answer 5

Potential alteration, loss of protein structure and function, altered levels of expression. Often lethal

Question 6

Define ‘quasispecies’

Answer 6

A group of viruses related by a similar mutation/s, competing within a highly mutagenic environment

Question 7

Describe recombination

Answer 7

Related (homogolous) sequences on 2 different virus genomes switch. Homogolous recombination. Can also occur between cells and viral genome sequences

Question 8

Describe reassortment

Answer 8

1. 2 viruses infect the same cell
2. One or more genes is transfered between the 2 viral genomes to create a novel combination
   * occurs in segmented RNA viruses*

Question 9

What are the consequences to viruses of recombination?

Answer 9

Lethal mutation, silent mutation, persistant damage, persistant advantage

Question 10

What are the properties of an influenza virus?

Answer 10

Important envelope glycoproteins - H, N
Genome consists of 8 linear RNA segments
Enveloped

Question 11

What does ‘H’ stand for?

Answer 11

Haemagglutinin - major antigen for neutralising antibodies. Binds to host receptors

Question 12

What does ‘N’ stand for?

Answer 12

Neuraminidase - releases progeny of the virus from the cell surface

Question 13

How can changes to H and N occur?

Answer 13

Antigenic drift and antigenic shift

Question 14

Describe influenza infection in birds

Answer 14

Affects alimentary tract in wild aquatic birds
Largely asymptomatic
Transmitted by faecal/oral route
All H and N types

Question 15

In which species is influenza most prominent?

Answer 15

Horses, dogs, pigs and humans

Question 16

How many H and N variants are there?

Answer 16

H - 16

N-9

Question 17

Define ‘antigenic drift’

Answer 17

Gradual accumulation of minor antigenic changes in surface proteins over time.

Question 18

Define ‘antigenic shift’

Answer 18

Exchange of whole genome segments between 2 influenza viruses, potentially causing a major antigen change

Question 19

How are influenza virons activated to cause disease?

Answer 19

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

Question 20

What are the public health implications of viruses?

Answer 20

Viruses are dynamic, meaning new diseases are constantly emerging

Question 21

Define ‘emerging/re-emerging disease’

Answer 21

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

Question 22

Define ‘epidemic’

Answer 22

Spread of disease to many individual

Question 23

Define ‘pandemic’

Answer 23

Spread of disease on a global scale

Question 24

How are new diseases emerging in animals and humans?

Answer 24

1. Change in mans interaction with the environment and alteration of it
2. Changing dynamic of animal/human populations
3. Climate effects (e.g. shifting insect populations)
4. Capacity of viruses to change

Question 25

How can zoonotic viruses emerge from a wildlife reservoir?

Answer 25

1. Interspecies contact
2. Cros-species virus transmission
3. Sustained transmission in new species
4. Virus adaptation to new species

Question 26

How can influenza be controlled?

Answer 26

Vaccination
Antiviral drugs
Isolation of patients
Education
Hygiene strategies
Surveillance
Development of new vaccines