Introduction to Viruses

Question 1

What size are viruses?

Answer 1

Small, from 20-400 nm in diameter

Question 2

Viruses are non-cellular.
What does this mean?

Answer 2

Genetic element that cannot replicate independently of a living (host) cell

Question 3

Name the three structures a virus could have.

Answer 3

Icosahedral, Helical or Complex.

Question 4

Describe the Icosahedral structure of a virus.

Answer 4

20 faces, each an equilateral triangle

Question 5

Describe the helical structure of a virus?

Answer 5

Protein binds around DNA/RNA in a helical fashion

Question 6

Describe the complex structure of a virus.

Answer 6

Simple- just neither helical or icosahedral.

Question 7

Where do viruses replicate?

Answer 7

Only replicate inside a host cell.

Question 8

What types of cells do viruses infect?

Answer 8

Most viruses have a specific host range and only infect specific host cell types.

Question 9

What is the study of viruses?

Answer 9

Virology

Question 10

Define virion.

Answer 10

Extracellular form of a virus.

Question 11

Where does a virion exist?

Answer 11

Exists outside host and facilitates transmission from one host cell to another

Question 12

What do virions contain?

Answer 12

Contains nucleic acid genome surrounded by a protein coat and, in some cases, other layers of material

Question 13

List the ways a virus family can be classified.

Answer 13

According to-
-Virion shape / symmetry
-Presence / absence of envelope
-Genome structure
-Mode of replication

Question 14

Name the four ways a virus can be classified regarding taxonomy.

Answer 14

Order, family, genus and species.

Question 15

Describe the structure of a virion.

Answer 15

Basically-
Nucleic acid is enclosed in a protein capsid which is then enclosed in a lipid envelope.
There are spike projections covering the virion.

Question 16

How do viruses replicate?

Answer 16

1. Viruses attaches to cell wall.
2. Virus becomes uncoated so leaves it’s outside.
3. Protein capsid and nucleic acid enter the host cell to allow replication of the nucleic acid.
   4.Protein synthesis occurs.
4. Genomic nucleic acid synthase and newly synthesised virus proteins get assembled to produce the new virion.
5. New virion is released to go and infect another cell.

->this wasn’t explained v well tbh did the best i could

Question 17

List a few of the many ways transmission can take place.
Give examples

Answer 17

Blood borne (HIV, Hep b)
Sexually transmitted (HIV, Hep b)
Vertically transmitted (HIV, Hep b)
Droplet (influenza)
Air borne. (measles, chickenpox).

Question 18

Name some viruses which only effect humans.

Answer 18

Smallpox or measles.

Question 19

Name a virus which can affect the respiratory syndrome.

Answer 19

Influenza.

Question 20

Give an example of a virus which can affect the neurological syndrome.

Answer 20

Polio

Question 21

There are many consequences of viral infection.
Name four consequences.

Answer 21

1. Clearance of virus
2. Chronic infection
3. Latent infection
4. Transformation

Question 22

Give an example of a virus which as the following consequence-
Clearance of virus.

Answer 22

Measles- long term immuinity.

Question 23

Give an example of a virus which as the following consequence-
Chronic infection.

Answer 23

HIV, Hepatitis B or C

Question 24

Give an example of a virus which as the following consequence-
Latent infection.

Answer 24

Herpes

Question 25

Give an example of a virus which as the following consequence- Transformation

Answer 25

Epstein-Barr Virus, Human Papillomavirus

Question 26

Describe viral latency.

Answer 26

Some viruses lay dormant in the body following primary infection. The full viral genome is retained in the host cell, but its expression is restricted, such that few viral antigen and no viral particles are produced. If tested, the virus will not be detected.

Question 27

What can happen to viruses undergoing viral latency?

Answer 27

Reactivation of viral replication can occur Reactivations may or may not cause apparent disease Reactivation more likely to occur and more severe in immunocompromised hosts

Question 28

Give two examples of viruses which undergo viral latency.

Answer 28

Herpes Simplex Virus Varicella Zoster Virus- chickenpox

Question 29

Reactibation of Varicella Zoster Virus- (chickenpox) can lead to what?

Answer 29

Shingles.

Question 30

Some viruses can lead to serious conditions uch as?

Answer 30

Cancer but other processes are often required too.

Question 31

Describe some mechanisms which may cause cancer.

Answer 31

1. Modulation of cell cycle control (driving cell proliferation) 2. Modulation of apoptosis (prevention of programmed cell death) 3. Reactive oxygen species mediated damage (some persistent viral infections can cause persistent inflammatory processes which lead to cancer via reactive oxygen species)

Question 32

How can we detect viruses?

Answer 32

1. Whole organisms 2. Part of organism e.g. antigen or nucleic acid 3. Immune reponse to an antigen using antibodies.

Question 33

Give an example of a virus that can lead to cancer

Answer 33

Human Papillomavirus (HPV): cervical, anal, oropharyngeal cancers

Question 34

Name the two ways of looking at the virus organism as a whole.

Answer 34

Using microscopy or culturing.

Question 35

Explain how we can look at part of an organism in order to detect a virus.

Answer 35

DNA/RNA detection by extraction of genetic material from a sample Amplification of region of target organism genome (if organism present in sample)

Question 36

Explain how immune response may allow us to detect a virus.

Answer 36

May be used to determine: Acute / recent infection Prior infection / response to vaccination

Question 37

What does virostatic mean?

Answer 37

Drug which inhibits viral replication

Question 38

What is a virucide?

Answer 38

A virucide is any physical or chemical agent that deactivates or destroys viruses.

Question 39

Are antiviral agents virostatic or virucidal?

Answer 39

All antiviral agents are virustatic, none are virucidal

Question 40

What are antivirals used for?

Answer 40

1. Prophylaxis (to prevent infection) 2. Pre-emptive therapy (when evidence of infection/replication detected, but before symptoms are apparent) 3. Overt disease 4. Suppressive therapy (to keep viral replication below the rate that causes tissue damage in an asymptomatic infected patient)

Question 41

How is viral infection prevented?

Answer 41

1. Vaccinations /immunisations 2. Prophylactic treatment post exposure 3. Infection prevention and control measures 4. Blood/tissue/organ screening 5. Antenatal screening

Question 42

If immediate protection, what can be done?

Answer 42

Passive immunisation with immunoglobulin

Question 43

List the ways a virus can be eradicated.

Answer 43

1. No animal reservoir or ability to amplify in the environment 2. Clearly identifiable, with accurate diagnostic tool 3. No chronic carrier state 4. Efficient and practical intervention, e.g. vaccination 5. Political / social support

Question 44

Name sa virus that has already been eradicated.

Answer 44

Smallpox.