Infection 18 - Influenza

Question 1

Describe the structure of the influenza virus

What are the 2 main surface antigens?

Answer 1

• Spherical, enveloped virus with segmented, negative single stranded RNA genome, containing 8 genes encoding for 11 proteins.
• 1) Haemagluttinin (H) - 18 types - binds to host cells
• 2) Neuraminidase (N) - 11 types - releases virus from host cell surface

Question 2

What are the differences between Influenza A, B + C in terms of what they infect + whether they undergo antigenic shift/drift?

Answer 2

A = Many animals, undergoes shift + drift and responsible for epidemics + pandemics. Birds are main animal reservoir.

B = Affects older humans + undergoes antigenic drift

C = Humans & pigs, undergoes antigenic drift

Question 3

What are the 3 potential routes of influenza transmission?

Answer 3

Transmitted via respiratory route (coughing, sneezing, inhaling)

1) Small-particle aerosols - <10uM remain in the air for hours
2) Larger particles or droplets - tall to the ground + infect with direct contact
3) Particles land on surfaces - infection through indirect contact

Question 4

What 3 innate immune barriers does the virus have to pass to cause infection?

Answer 4

1) Respiratory epithelial cells covered in mucus trap virus
2) Ciliated respiratory epithelial cells sweep mucus up from LRT to URT where its swallowed
3) Secretory IgA, NK cells and macrophages in the lung

Question 5

How does the virus enter + leave cells (H + N)?

Answer 5

• H binds to scialic acid host receptor (NANA residue) then enters via receptor mediated endocytosis
• H binds scialic acid again, N cleaves scialic acid allowing virus to leave surface of host cell

Question 6

What are the symptoms of influenza infection?
What is the incubation period?
What are the potential complications that account for most deaths?

Answer 6

• Fever, sore throat, headache, dry cough, fatigue, fatigue etc
• 1-5 days (avg 2-3)
• Young children, elderly, underlying conditions + pregnant women most at risk. Respiratory and neurological complications can be fatal.

Question 7

How is influenza diagnosed?

Answer 7

• Typically through history + symptoms but RT-PCR and antigen tests are available.

Question 8

What are the treatment options for influenza?

Answer 8

1) M2 inhibitors - rimantadine, inhibit M2 protein and therefore viral uncoating
2) Neuraminidase inhibitors - tamiflu, inhibits release from infected cell
3) Vaccine - formalin-inactivated vaccine by injection, nasal spray (live attenuated) for children.

Question 9

What is antigenic drift?
Why does it occur?
What are the implications?

Answer 9

• Minor changes in the genes of the flu virus (particularly H+N) that occur gradually over time causing seasonal epidemics, not a change in viral subtype.
• Life cycle only 6 hours, high error rate of RdRp’s + constant replication of flu virus - causes random mutations in viral RNA
• WHO monitors variation and determines components of winter flu vaccine

Question 10

What is antigenic shift?
Why does it occur?
What are the implications?

Answer 10

• Major changes in the H/N proteins of the virus
• Occurs when the genes of two or more influenza virus strains combine in a single organism, resulting in a ew viral subtype
• Potentially no immunity to new strain, cause of widespread epidemics/pandemics.