Influenza

Question 1

Influenza

Answer 1

-ssRNA
its RNA genome is 8 segments
4 HA Haemagglutinin (entry)
6 NA Neuraminidase (exit)

Question 2

Influenza A

Answer 2

A Pandemics- infects humans, birds, pigs, horses etc

Question 3

Influenza B

Answer 3

B Seasonal epidemics- infects only humans
Less common that Influenza A
Mutates 2-3 times slower than Influenza A

Question 4

Influenza C

Answer 4

C Mild respiratory illness- infect humans and pigs
No HA, NA

Question 5

How influenza viruses infect target cells

Answer 5

Influenza virus haemagglutinin (HA)
mediates entry into target cells
Through targeting a 2 6 sialic acid

Initially HA binds to sialic acid receptors on the outer cell membrane, trimerises, then the HA1 and HA2 subunits get cleaved. This triggers endocytosis.

In the endosome the pH drops, triggering a conformational change. The HA1 folds back out of the way, enabling the HA2 to insert its fusion peptides into the endosomal membrane. This will result in the fusion of the viral envelop with the endosomal membrane, generating a pore through which the nucleic acid is released to the cytoplasm

Question 6

How Neutralizing Antibodies Against Influenza Viruses Work

Answer 6

Targeting Hemagglutinin (HA): Neutralizing antibodies primarily target the HA protein, preventing the virus from binding to sialic acid receptors on host cells.

Blocking Entry: By binding to HA, these antibodies prevent the virus from entering host cells, effectively neutralizing the infection.

Question 7

Antigenic Variation and Its Impact on Neutralizing Antibodies

Answer 7

Antigenic Drift: Small, gradual mutations in HA and NA genes due to errors in viral replication lead to changes in antigenic sites. This results in reduced effectiveness of existing antibodies, requiring updates to seasonal vaccines.

Antigenic Shift: A major change due to the reassortment of gene segments between different influenza A viruses, leading to new HA/NA combinations. This can result in the emergence of a novel virus against which the population has little or no immunity, potentially causing pandemics.