Influenza Virus + Genetic Change

Question 1

what causes virsues to emerge

Answer 1

1. change in mans interaction with environment + destruction
2. changing dynamic of animal/human populations
3. climate effects
4. changed farming practices
5. social practices

Question 2

what are genetic changes in viruses

Answer 2

1. genetic stability: maintenance of virus genotype from generation to generation
2. genetic variation: emergence of new viral strains –> new biological properties, consequences of mutation and selection
3. spotaneous mutation
4. genetic exchange between viruses

Question 3

what are the two sources of genetic change

Answer 3

1. mutation = change in the nucleotide sequence of genome
2. genetic exchange of material between two viruses

Question 4

what is a spontaneous mutation

Answer 4

random mutation of viral genome occurs during replication

insertions/deletions/rearrangements

Question 5

what is quasispecies

Answer 5

nucleotide change but no amino acid change

potential alteration/loss protein structure/function, altered levels of expression –> potential fitness change

Question 6

how do genes transfer between viruses

Answer 6

recombination or reassortment

potentially large change to genome involving swap of gene segments/entire from different virus genomes

Question 7

what is recombination

Answer 7

two viruses exchange genetic segments

Question 8

what is reassortment

Answer 8

occurs in segmented RNA viruses –> transfer of one or more genes –> novel combination

Question 9

what are the consequences to viruses of genetic changes

Answer 9

1. lethal mutation
2. silent mutation
3. persistence disadvantage
4. persistence advantage

Question 10

what causes the viruses to develop new strains

Answer 10

selection pressures favour establishment of new strains

emergence of mutants which are better equipped for survival and spread

Question 11

what are selection pressures that can facilitate emergence of new virus strains

Answer 11

1. immunity of target population –> antigenic variants
2. altered physiological environment - new host, new tissue –> variants with altered antireceptor(s) +/- intracellular properties
3. altered population dynamics of the host –> variants with altered pathogenicity
4. medical intervention - antiviral drug –> drug resistant variants

Question 12

what type of virus is influenza A

Answer 12

orthomyxovirus

envelope glycoproteins

Question 13

what are major antigens of influenza A virus

Answer 13

hemagglutinin (H/HA)

neuraminidase (N/NA)

major antigens of virus

Question 14

what is hemagglutinin

Answer 14

major antigen for neutralizing antibody

binding host receptor

Question 15

what is neuraminidase (N)

Answer 15

release of progeny virus from cell surface

Question 16

how do changes of hemagglutinin and neuraminidase occur

Answer 16

by antigenic drift and antigenic shift

Question 17

how big is the influenza A genome

Answer 17

8 linear segments

H & N encoded by separate segments

Question 18

what serotypes of hemagglutinin and neuraminidase exist in nature

Answer 18

18H and 11N

Question 19

what is the reservoir for influenza A in avian species

Answer 19

wild aquatic birds (waterfowl and shorebirds) - alimentary or resp tract

Question 20

what is the infection of influenza A virus in avians

Answer 20

asymptomatic

Question 21

how is influenza virus A transmitted

Answer 21

fecal/oral (waterborne)

Question 22

what are the serotypes of influenza A viruses

Answer 22

16H and 9N types

Question 23

how are mammals infected with influenza A

Answer 23

aeosol

Question 24

what is the influenza A infection in mammals

Answer 24

respt tract

Question 25

what are the H and N types in mammals of influenza A

Answer 25

limited H and N types

equine, canine, swine, human influenza

capacitty for cross species spread within mammals and between avians and mammals

Question 26

what is antigenic drift

Answer 26

spontaneous mutations in surface antigen –> minor change in H/N –> potential for selection of antigenic variants in a partially immune population (those which partially evade immune response to the “consensus” circulating strain)

emergence of new strains with altered antigenicity against vaccine might be less effected –> reasons for updates

Question 27

what is an antigenic shift

Answer 27

major change in surface antigenicity (due to reassortment) –> one or both of surface glycoproteins (H/N) are changed to different antigenic type (ex. H1N1 –> H2N2)

if reassortment emerges which can pass efficiently man-man –> potential pandemic

Question 28

what is host range change

Answer 28

can infect cross species

Question 29

what is change in pathogenicity

Answer 29

low pathogenicity (LPAI) –> high pathogenicity avian influenza (HPAI)

Question 30

what is antiviral drug resistance

Answer 30

monitoring, awareness, changed practice