An Introduction to Viruses

Question 1

What can you say about the size of viruses?

Answer 1

They are very small, being only 20-400nm in diameter

Question 2

What can you say about cells, viruses and replication?

Answer 2

Viruses are non-cellular so genetic elements cannot replicate independent of a host

Question 3

What are different structures of viruses?

Answer 3

Icosahedral (20 faces, each in an equilateral triangle)

Helical (protein binds round DNA/RNA in a helical fashion)

Complex (neither of above)

Question 4

What can you say about the host range of viruses?

Answer 4

Many viruses have a specific host range and can only infect specific host cell types

Question 5

Can viruses be grown in a lab dish?

Answer 5

No, because they need a cell to act as a host

Question 6

What are examples of icosahedral viruses?

Answer 6

Polio

Rhino

Adeno

Question 7

What is an example of a helical virus?

Answer 7

Tobacco mosaic virus

Question 8

What is a virus?

Answer 8

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

Question 9

What is virology?

Answer 9

The study of viruses

Question 10

What is a virion?

Answer 10

Extracellular form of a virus

Question 11

Where do virions exist and what do they do?

Answer 11

They exist outside of the host and facilitates transmission from one host cell to another

Question 12

What do virions contain?

Answer 12

Nucleic acid genome surrounded by a protein coat and in some cases other layers of material

Question 13

What are virus families classified according to?

Answer 13

Virion shape/symmetry

Presence/absence of envelope

Genome structure

Mode of replication

Question 14

What do envelopes do to a virus?

Answer 14

Makes them much more fragile, making them easier to kill and cannot survive outside the body for a long time

Question 15

What are examples of enveloped viruses?

Answer 15

Flu

HIV

Hep C

Question 17

Where are lipid envelopes stolen from?

Answer 17

The host cell the virion came out of

Question 18

What is the process of virus replication?

Answer 18

1) Replication of genomic nucleic acid
2) Virion assembly
3) Virion released from cell and attaches to another
4) Uncoats inside the other cell
5) Replication of genomic nucleic acid

Question 19

What are different kinds of transmission?

Answer 19

Blood borne

Sexual

Vertical

Faecal-oral

Droplet

Airborne

Close contact

Vector borne

Zoonotic

Question 20

What can you say about the kinds of animals viruses can infect?

Answer 20

Some viruses can only infect humans whereas some can infect a range of animals, leading to recombination and generation of new strains

Question 21

What does viruses infecting many kinds of animals lead to?

Answer 21

Recombination and generation of new strains

Question 22

What are the possible consequences of viral infection?

Answer 22

Clearance of virus (no short or long term immunity)

Chronic infection

Latent infection (virus lies dormant)

Transformation (long term infection with altered cellular gene expression)

Question 23

What happens when viruses lie dormant?

Answer 23

Full virus genome is retained in the host cell but expression is restricted, but reactivation may occur

Question 24

What are examples of viruses that can lie dormant?

Answer 24

Herpes simplex virus

Varicella zooster virus

Question 25

How can viruses lead to cancer?

Answer 25

Modulation of cell cycle control (driving cell proliferation)

Modulation of apoptosis (prevention of programmed cell death)

Reactive oxygen species damage (causes inflammatory response which lead to cancer via oxygen species)

Question 26

What aspects of a virus can be detected?

Answer 26

Whole organism

Part of organism (such as antigen or nucleic acid)

Immune response to a pathogen (such as an antibody)

Question 27

What can the whole organism be detected by?

Answer 27

Microscopy

Culture

Question 28

What is not really used anymore?

Answer 28

Electron microscopy and cell culture

Question 29

Why is cell culture not practical?

Answer 29

Works well but has a large time lag

Question 30

What can looking at the immune response determine?

Answer 30

Acute/recent infection

Prior infection/response to vaccination

Question 31

What does virustatic mean?

Answer 31

Stopping the growth of viruses

Question 32

What are all antiviral agents?

Answer 32

Virustatic

Question 33

Why are there limited viral proteins for antiviral agents to target?

Answer 33

Because viruses utlilise a host cells enzymes

Question 34

What may antiviral agents be used for?

Answer 34

Prophylaxis (to prevent infection)

Pre-emptive therapy (evidence of infection is detected but before symptoms are present)

Overt disease

Suppressive therapy (keep viral replication below the rate that causes tissue damage)

Question 35

What is prophyaxis?

Answer 35

To prevent infection

Question 36

What is pre-emptive therapy?

Answer 36

When there is evidence of infection but before symptoms are present

Question 37

How can viruses be prevented?

Answer 37

Immunisation (vaccination/passive immunisation with immunoglobin)

Prophylactic treatment post exposure

Infection prevention and control measures

Blood/tissue/organ screening

Antenatal screening

Question 38

What is eradication?

Answer 38

Permanent reduction to 0 of worldwide incidences of infection

Question 39

What properties do viruses need to have to be eradicated?

Answer 39

No animal reservoir or ability to amplify in the environment

Clearly identifiable

No chronic carrier state

Efficient and practical intervention (such as vaccination)

Political/social support

Question 40

What is an example of a virus that has been eradicated?

Answer 40

Smallpox