Viruses

Question 1

What is a virus?

Answer 1

A genetic element that cannot replicate independently of a living (host) cell.

Question 2

What are some basic facts about viruses?

Answer 2

They can have different structures i.e.

• isohedral (20 faces, equ triangle, eg polio, rhino),
• helical
• complex

Non-cellular i.e. cannot live without a host cell

Have a specific host range and can only infect specific host cell types

Question 3

What is a virion?Describe its function and structure.

Answer 3

-The extracellular form of a virus.
-It exists outside the host cell.facilitates transmission from one host to another.
-Wraps the virus in a protein coat/capsid which is the infective form.
It contains nucleic acid genome surrounded by a protein coat.

Question 4

How can viruses be transmitted?

Answer 4

Blood borne 
Sexual
Vertical
Faecal-oral
Droplet
Airborne
Close contact
Vector borne

Question 5

Give example of blood borne, sexual, vertical transmission of a virus.

Answer 5

Blood borne- HIV, Hepatitis B, Hepatitis C

Sexual- HIV, Hepatitis B

Vertical- HIV, Hepatitis B

Question 6

Give example of Faecal-oral, droplet and airborne transmission of a virus?

Answer 6

Faecal-oral: Hepatitis A, Hepatitis E, Polio

Droplet- Influenza

Airborne- Measles, chickenpox

Question 7

Give example of close contact and vector borne transmission of a virus?

Answer 7

Close contact- herpes

Vector borne- yellow fever

Question 8

What are the consequences of viral infection?

Answer 8

• Clearance of virus, with no short or long-term immunity. Eg Hepatitis C
• Chronic infection Eg HIV, Hepatitis B
• Latent infection Eg Herpes
• Transformation which is long term infection with altered cellular gene expression Eg Epstein-Barr virus

Question 9

What is viral latency?

Answer 9

Following primary infection, some viruses lay dormant in the cell. 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.

Question 10

What can occur in viral latency?

Examples?

Answer 10

REACTIVATION of viral replication. Reactivations may or may not cause the apparent disease. It is more likely to occur and be more severe in the immunocompromised.
Eg Herpes Simplex Virus and Varicella Zoster Virus

Question 11

What are some viruses that lead to cancer?

Answer 11

Human papilloma virus (HPV): cervical, anal, oropharyngeal cancer

Hepatitis B and Hepatits C: hepatocellular carcinoma

Question 12

What are detection methods of viruses for whole organisms

Answer 12

Whole organisms- use microscopy, culture

Question 13

How can you prevent viral infections?

Answer 13

Immunisation i.e. vaccination or passive immunisation with immunoglobulin

Infection prevent and control means i.e. isolation of symptomatic patients, PPE, safe use and disposal of sharps

Antenatal screening

Question 14

When can viruses be eradicated?

Examples?

Answer 14

Viruses with:

• No animal reservoir or ability to amplify in the environment
• Clearly identifiable, with an accurate diagnostic tool
• vaccination
• Political and social support

Examples: Smallpox, measles, polio

Question 15

Detection method for viruses in parts of organisms?

Answer 15

Parts of organisms i.e. antigens, nucleic acid.

• It uses antigen detection.
• This involves DNA/RNA detection which is based on the extraction of genetic material from the sample. -Amplification of region of target organism genome (if the organism is present in the sample)

Question 16

Detection method for viruses in Immune response to a pathogen and when is it used?

Answer 16

• Immune response to a pathogen uses similar methods to antigen detection.
• May be used to determine an acute/recent infection or prior infection/response to vaccination