Lecture 4 Antivirals against influenza virus

Question 1

Name the 3 components that classify the influenza virus

Answer 1

RNA
-ve stranded
segmented
Orthomyxoviridae

Question 2

How many flavours of influenza are there?

Answer 2

3 - influenzavirus A-C

Question 3

Which is the most common influenza in humans?

Answer 3

Influenzavirus A

Question 4

What flavour does the Australian flu come under?

Answer 4

Influenzavirus B

Question 5

What is the lipid bilayer of the virus made from?

Answer 5

plasma membrane of the previously infected cell

Question 6

Which variant M glycoproteins does influenzas A-C encode for?

Answer 6

Influenza A = AM2 protein
Influenza B = BM2 protein
Influenza C = CM2 protein

Question 7

What is the difference between low pathogenicity seasonal flu and high pathogenicity influenza strains?

Answer 7

low pathogenicity seasonal flu - mild and common type of flu

high pathogenicity influenza strains - rare and severe, can cause deaths

Question 8

name 2 examples of high pathogenicity influenza strains

Answer 8

Avian influenza (H5N1)
Spanish influenza (H1N1)

Question 9

How is influenza virus transmitted?

Answer 9

Droplet inhalation - sneeze, cough, breathing = small droplets enter the resp tract
Direct contact - sneezing, coughing and breathing = droplets on surfaces called fomites, contact between surfaces and mucosal cells, mediated by contaminated hands/fingers

Question 10

What are the symptoms of influenza virus?

Answer 10

Upper resp tract cells affected
Symptoms have rapid onset (24h after contact), peak at day 3, persist for 8/9 days 
Tiredness
Sore throat
Runny nose
Headache
Fever
Cough
Muscle aches

Question 11

What are the 3 membrane proteins on the influenza virus?

Answer 11

M2 protein - specific to flavour of influenza
Neuraminidase (NA)
Haemoglutanin (HA)

Question 12

What shape is the influenza virus?

Answer 12

Rod shaped

Question 13

What is the the matrix protein?

Answer 13

The sheeth beneath the membrane [see slide for image]

Question 14

Describe the influenza virus life cycle

Answer 14

[see slide for image]
Virus binds sialic acid receptor via HA, becomes internalised → Low pH membrane fusion via HA → segments released into cytoplasm → segments imported into nucleus → RNA synthesis → RNA/RNP export → virus assembly at plasma membrane → release of viron

Question 15

Explain step 1 virus attachment of influenza virus

Answer 15

HA recognises sailic acid on the surface of cilliated epithelial cells
HA binds to sialic acid via galactose protein

Question 16

Explain step 2/3 virus entry of influenza virus

Answer 16

Virus is inside the endosome
Escapes when virus envelope (matrix layer) fuses with endosome membrane - mediated by HA protein changing confirmation due to low pH
8 RNA protein segments still cannot get out - release is mediated by M2 protein
M2 (ion channel) forms a pore = influx of H+ ions
Matrix protein layer breaks down and segments are released [see slide for image]

Question 17

Explain step 8 virus release of influenza virus

Answer 17

Virus now needs to infect new cells via HA and sialic acid receptor
Need to make sure that HA on released viruses does not bind to receptor on the old cell as this would mean the virus does not spread
Controlled by the NA protein on the virus cell membrane
NA cleaves sialic acid from previously infected cell (essential role)
[see slide for image]

Question 18

Why is a new vaccine needed for influenza every year

Answer 18

Influenza virus is rapidly mutating

Every year there is a different strain of the virus

Question 19

Why is a stockpile of antiviral medication for influenza needed despite there being vaccines?

Answer 19

Vaccine is slow to make - 9 months
If a pandemic occurred then it would not be quick enough to make a vaccine
Antiviral would work against many strains

Question 20

Name the 2 ways that influenza virus mutation occurs

Answer 20

Antigenic drift

Antigenic shift

Question 21

What is antigenic drift?

Answer 21

When enzyme genes are copied, mistakes are made
Incorporation of single nucleotide changes into genome
Leads to new virus formation

Question 22

What is antigenic shift?

Answer 22

Occurs when 2 different cells infect the same virus

Allows genome segments to mix when virus assembly occurs = different proteins encoded

Question 23

What are the 2 current targets for influenza antivirals?

Answer 23

M2 protein

Neuraminidase cleaving protein

Question 24

What are 2 names of drugs in the adamantanes class?

Answer 24

Amantadine

Rimantadine

Question 25

Which influenza families does adamantanes target?

Answer 25

Low conc = specific for influenza A | High concentration = some general antiviral activity

Question 26

What are the pros of adamantanes?

Answer 26

Cheap Effective Given as oral or aerosol

Question 27

What are the cons of adamantanes?

Answer 27

Must be administered early before the infection e.g. before day 2 Most influenza viruses now resistant due to drift mechanism - mutation in M2 channel Therefore no longer approved by FDA to treat influenza

Question 28

What is the mechanism of action of adamantanes?

Answer 28

``` Prevent M2 ion channel activity Blocks either of the 2 binding sites: Within the central pore Within a membrane facing pocket - one of each of the monomers of the tetramere = prevention of ion channel activity Matrix layer remains intact Virus cannot exit the endosome ```

Question 29

What is the mechanism of action of Relenza (zanamir) and oseltamivir (tamiflu)?

Answer 29

Mimic sialic acid - blocks neurominidase active site so it can no longer bind and digest sialic acid Produced based on the contact sites between the sailic acid in the neurominidase active state Produced a molecule that bound with a higher affinity by adding a guanidino group to Glu119 at C4 = now interacts with Glu 225 and Asp 151

Question 30

Do neurominidase inhibitors work?

Answer 30

Moderately Must be given very early on in infection i.e. 48 hours Symptoms are reduced by 1 day = little impact Is it worth it? well it may be enough to slow pandemic spread Stockpiles of Relenza (zanamir) and oseltamivir (tamiflu) exist

Question 31

Are neurominidase inhibitors at risk of resistance?

Answer 31

Should not encounter resistance problems as similar structure to sailic acid However 1% of seasonal strains have shown resistance