Virology

Question 1

What are viruses?

Answer 1

Obligate intracellular parasites that require another living cell to infect to replicate within

Question 2

What is the structure of viruses?

Answer 2

Helical, symmetrical around central axis
Icosahedral, made up of capsomeres

Question 3

What are the classifications of viruses?

Answer 3

Genetic material
Segmented/non-segmented
Genome linear/circular
Single stranded/double stranded

Question 4

What are the modes of transmission?

Answer 4

Air borne
Faeces-oral
Bodily fluids
Vectors

Question 5

What are the steps of replication?

Answer 5

Attachment
Penetration
Uncoating
Replication
Assembly
Release

Question 6

Explain uncoating

Answer 6

pH/enzyme action change

Question 7

Explain replication

Answer 7

Nucleic acid and protein synthesis

Question 8

What are the steps of viral replication (entry and exit)?

Answer 8

Invade host - entry
Skin/mucous membrane
Vertical transmission
Protein on virus that binds to EXC receptors
Localised infection
Haematogenous/neural spread
Host cell proteases - exit

Question 9

Explain latency and reactivation

Answer 9

Viral nucleic acid -> pathogenic genes supressed -> genes transcribed and translated -> pathogenic infection -> disease

Question 10

What are the common pathogens?

Answer 10

Blood borne pathogens
Respiratory tract infections
Skin infections
GI infections
STI
Hospital acquired infections
Vector borne pathogens

Question 11

Explain influenza

Answer 11

Orthomyxoviridae
100-200nm diameter spherical virion
Lipid envelope
segmented (-)sense single strand RNA

Question 12

Why is HA1 important?

Answer 12

Important for receptor binding site
Mutations may alter receptor binding

Question 13

Why is HA2 important?

Answer 13

Anchor function
Forms stalk

Question 14

Why is the NA tetramer important?

Answer 14

Important in releasing the virus from host cell

Question 15

What does oseltamivir target?

Answer 15

neuraminidase protein

Question 16

What is neuraminic (sialic) acid?

Answer 16

Sugar group on glycosylated molecules
Allows influenza to bind to multiple cell types
Tropism

Question 17

What does the M2 ion channel do?

Answer 17

Allow influx of protons during replication

Question 18

What does M1 ion channel do?

Answer 18

Beneath lipid membrane and stabilises structure

Question 19

What is the pathogenesis of influenza?

Answer 19

Air-borne
Destroys cilia

Question 20

Explain the pathogenesis of influenza

Answer 20

Upper RT replication of virus
Innate/adaptive immune system response triggered by vRNA recognition
Pattern recognition receptors (PRRs) stimulate cytokine and chemokine production
Immune cells stimulated and migrate to infection site

Question 21

Explain the replication process in influenza

Answer 21

Low affinity binding HA to NA which triggers activation of receptor tyrosine kinase cascade
Receptor-mediated endocytosis using clathirin
Low pH in endosomes induces conformational changes in HA which allows membrane fusion and release viral genome
Release of ribonucleoprotein complex which contain RNA pol.
New virions assemble in nucleus and move to cytoplasm
Assemble at plasma membrane and released by budding

Question 22

What are the two immune responses for influenza?

Answer 22

Humoral immunity: effective antibody production helps clear infection by neutralisation
Cell mediated immunity: cytotoxic T cells, alveolar macrophages

Question 23

What are the genetic variations of influenza?

Answer 23

RNA virus
RNA polymerase low fidelity enzyme
Segmented genome
Reassortment RNA genome fragments
Antigenic shift vs antigenic drift

Question 24

What is antigenic shift?

Answer 24

Gradual mutation in genes

Question 25

What is antigenic drift?

Answer 25

Sudden change in genes, creating new strains