Lec 15-Influenza Rep And Evolution

Question 1

Influenza virus structural components:

Answer 1

Have glycoproteins (yellow and green) in an envelope (blue). Under envelope is matrix protein (green), and virus has 8 genome segments

Question 2

2 major glycoproteins on influenza virus surface:

Answer 2

• HA: Binds to sialic acid and promotes attachment and entry
• NA (neuraminidase): Enzyme that removes sialic acid from cell surface, allowing progeny influenza viruses to escape the cell and spread to new hosts

Question 3

How do HA and NA work together?

Answer 3

Virus needs to escape from cell, but if virus has sticky HA exterior, NA helps get rid of it so virus can leave

Question 4

Why are HA and NA so important for influenza A?

Answer 4

• Influenza is very diverse, we sort diverse viruses via HA and NA proteins—subtypes of influenza are based on these proteins
• Influenza has 18 HA proteins and 11 NA proteins that have been identified

Question 5

HA and NA naming in influenza A

Answer 5

Has to do with viruses such as H1N1 and H5N1 i.e. H5N1 was HA 5 (of 18) and NA 1 (of 11)—group by being antigenically distinct, whether or not antibodies can neutralize them

Question 6

Antigenic distinction of HA and NA in influenza A

Answer 6

HA and NA are antigenically distinct—our antibodies bind to and identify these proteins. Binding to HA causes neutralization, blocking viral attachment to host. Neutralizing antibodies is a way our immune system protects us. Eg. Antibodies to H1 cant be neutralized by a virus with H2

Question 7

What are the natural reservoir hosts for influenza A?

Answer 7

Birds (exception is H17N10 and H18N11 host is bats)

Question 8

Which influenza A viruses are currently circulating in humans?

Answer 8

H1N1 and H3N2

Question 9

Is influenza B dangerous

Answer 9

Very

Question 10

How is influenza B divided?

Answer 10

Using same HA and NA antigenic distinction that influenza A does

Question 11

What animals does influenza B circulate in?

Answer 11

Only in humans, causing seasonal disease (therefore no concern of pandemic). No spillover from animals

Question 12

What are the strains of influenza B that are currently circulating?

Answer 12

Victoria and Yamagata —they are antigenically distinct (i.e. antibodies to Victoria dont neutralize Yamagata)

Question 13

What causes pandemics?

Answer 13

New influenza A subtypes

Question 14

Spanish flu stats

Answer 14

In 1918-19, 20-50million dead

Question 15

What are superspreader events?

Answer 15

Spread influenza throughout population. Eg. Philadelphia throwing WWI parade

Question 16

How does human behaviour affect influenza virus transmission?

Answer 16

Masking and social distancing can reduce pandemic

Question 17

When does influenza A and B spike?

Answer 17

Winter—influenza is seasonal!!! However winter 2021 had way less influenza cases due to heavy masking at the time

Question 18

Influenza A pandemics are ___

Answer 18

Deadly

Question 19

What has happened to influenza B viruses since COVID-19?

Answer 19

Yamagata has not been seen since

Question 20

Influenza virus evolution and vaccines:

Answer 20

Vaccines are re-made every year because circulating strains change and evolve each year

Question 21

2 methods of influenza evolution:

Answer 21

1. Antigenic drift: rapid mutation and selection of new strains that escape neutralizing antibodies; changes that allow virus to surpass immune sys (small changes in antibody)
2. Antigenic shift: circulating influenza viruses changing due to swapping of genetic material between viruses from spillover events from animal hosts to humans (big changes in antibody)

Question 22

Are influenza virus genomes (+) or (-)? ss or ds?

Answer 22

(-)ssRNA

Question 23

Segments of (-)ssRNA influenza virus genomes

Answer 23

8 segments, each attached to viral RdRp—virus has to bring in its own RdRp, cant use host mechanisms to create it. Because they are (-), they aren’t immediately ready to be translated upon entering host. When virus infects cell, genome goes to nucleus and attaches to RdRp there

Question 24

Viral RdRp is required to decode (-)ssRNA into:

Answer 24

1. Viral mRNAs with 5’ caps and poly A tails
2. (-)ssRNA genome copies
   +ssRNA intermediates

Question 25

Does RdRp make mistakes? What effect does this have?

Answer 25

Yes it makes a lot of mistakes. This supports rapid evolution, as we are sampling all possible genetic combos by making these mistakes

Question 26

What is antigenic drift?

Answer 26

Genes that are changing/encoding proteins on virus surface that antibodies recognize are HA and NA. Those changes could make bad proteins, or could make proteins that are different enough that antibodies can no longer bind. This results in antigenic drift: gradual viral evolution and evasion of host neutralizing antibodies. Antigens that drift are mostly on HA

Question 27

Why is the influenza virus that is circulating now different from the one last winter?

Answer 27

Antigenic drift

Question 28

Mutated amino acids in HA:

Answer 28

HA trimer —Effective antibodies pick on locations that overlap with binding to receptors. Mutated AAs interact w receptor, change so they cant be neutralized by antibody

Question 29

Why is antigenic drift a frequent cause of vaccine mismatches?

Answer 29

We have to select strains to put in vaccine that are ones that are circulating, but antigenic drift changes the circulating ones…makes it hard to pick

Question 30

Laver and Webster experiment

Answer 30

Wanted to understand where H2N2 virus came from—
- Experiment 1: Swabbed a bunch of birds—18 of them had antibodies to a human influenza. This means they have been exposed, not that they were carrying it. They injected it into chicken eggs and 1 egg grew the virus—now this means the virus was in the birds
- Experiment 2: Gathered antibody samples from victims of 1957 flu pandemic and avian flu strains, mixed the samples. Antibodies attacked bird strains, meaning human flu virus had some of the same molec features as avian flu viruses

Question 31

What is the major factor that allows influenza to cause pandemics?

Answer 31

Moving between host species (zoonotic), and antigenic shift (sharing genetic material between diff influenza viruses)

Question 32

How to create a virus with advantages?

Answer 32

Co-infection of target cells by diff strains of influenza to swap genetic material. This allows reassortment of genome segments in progeny. This is known as antigenic shift, creating a new virus not recognized by immune system

Question 33

Antigenic shift responsible for which pandemic?

Answer 33

2009 H1N1

Question 34

Highly pathogenic avian strain + human strain =

Answer 34

= new highly pathogenic human strain

Question 35

Animal example of antigenic shift:

Answer 35

Pigs are a good mixing vessel for influenza. They have the right kind of sialic acids to be infected with avian and human influenzas which will swap genomes to make a new virus

Question 36

What is the process like of selecting which antigens go into a vaccine with months of year outlined?

Answer 36

• Managed by WHO
• They are always doing surveillance abt circulating strains
  1. Jan/Feb: select strains and prepare reassortants (steps below)
  2. Feb-Apr: standardize antigen, make sure they work against immune response
  3. Summer: formulate/test/package/manufacture
  4. Fall: vaccinate

Question 37

Process of influenza vaccine development

Answer 37

Selecting HA and NA genes for all circulating strands you want in your vaccine —> clone them into plasmids —> combine these with 6 remaining standard genome segments —> insert 8 plasmids into cells, plasmids can start production of new viruses —> collect hybrid viruses that have correct HA/NA antigens at surface —> this forms basis for vaccine —> use it to inoculate eggs

Question 38

Which antigens are in our current influenza vaccine?

Answer 38

Influenza A H1N1
Influenza A H3N2
Influenza B HA and NA (Victoria)
Influenza B HA and NA (Yamagata)

Question 39

What could we change about current vaccine?

Answer 39

We could replace Yamagata with alternate H3N2 if its fully extinct, as there have been some problems with H3N2 mismatches, so adding another H3N2 strain may allow us to increase effectiveness against that strain

Question 40

Influenza mRNA vaccines?

Answer 40

Currently in clinical trials