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 flavors of influenza are there?

Answer 2

4 - influenzavirus A-D

Question 3

Which is the most common influenza in humans?

Answer 3

Influenzavirus A

Question 4

What flavor 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 - a 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 the 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 flavor of Influenza

Neuraminidase (NA)

Haemagglutinin (HA)

Question 12

What shape is the influenza virus?

Answer 12

Rod-shaped

Question 13

What is the matrix protein?

Answer 13

The sheet beneath the membrane

Question 14

Describe the influenza virus life cycle

Answer 14

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 recognizes sialic acid on the surface of ciliated epithelial cells HA binds to sialic acid via galactose protein

Question 16

Explain step 2/3 virus entry of influenza virus

Answer 16

The 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 proteins forms a pore = influx of H+ ions

Matrix protein layer breaks down and segments are released.

Question 17

Explain step 8 virus release of influenza virus

Answer 17

The virus now needs to infect new cells and needs to make sure that HA on released viruses does not bind to the receptor on the old cell as this would mean the virus does not spread.

Therefore, NA cleaves sialic acid from the previously infected cell (essential role).

Question 18

Why is a new vaccine needed for influenza every year

Answer 18

The influenza virus rapidly mutates

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

A 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

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

Question 22

What is an antigenic shift?

Answer 22

Occurs when 2 different viruses infect the same cell

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 the 2 names of drugs in the adamantanes class?

Answer 24

Amantadine

Rimantadine

Question 25

Which influenza families do 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 the 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:
  1) Within the central pore
  2) Within a membrane facing pocket
• Matrix layer remains intact because no H+ influx
• The virus cannot exit the endosome

Question 29

What is the mechanism of action of Relenza (zanamivir) and oseltamivir (Tamiflu)?

Answer 29

Mimic sialic acid - blocks NA active site so it can no longer bind and digest sialic acid.

Produced a molecule that bound with a 100x higher affinity for NA than sialic acid by adding a guanidino group to Glu119 at C4 = now interacts with Glu 225 and Asp 151.

Question 30

Do neuraminidase (NA) 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 (zanamivir) and oseltamivir (Tamiflu) exist

Question 31

Are neuraminidase (NA) inhibitors at risk of resistance?

Answer 31

Should not encounter resistance problems as a similar structure to sialic acid.

However, 1% of seasonal strains have shown resistance