Viruses mw % +

Question 1

Virus Basics

Answer 1

• Obligate intracellular pathogens (can only replicate inside host cell)
• Most viruses have a specific host range and only infect specific host cell types (tissue tropism)

Question 2

Virus families classification (4)

Answer 2

Can be classified according to:

• Virion shape / symmetry
• Presence / absence of envelope
• Genome structure
• Mode of replication

Question 3

Virion Structure pic

Answer 3

Question 4

Virus Replication pic►

Answer 4

Question 5

Transmission pic

Answer 5

Question 6

Host Range

Answer 6

1. Some viruses may only infect humans, e.g. smallpox, measles,
2. Some may also infect other animals / birds:

• Transmission of a novel (not seen before) virus to humans
• Coinfection of human and animal or bird strains in one organism may lead to recombination and generation of a new strain

Question 7

Consequences of viral infection

Answer 7

1. Clearance of virus (with no, short or long term immunity):

• Hepatitis C (no lasting immunity)
• Measles (long term immunity)

2. Chronic infection

• HIV, hepatitis B, hepatitis C

3. Latent infection

• Transformation (long term infection with altered cellular gene expression)

•Epstein-Barr Virus, Human Papillomavirus

Question 8

Viral Latency

Answer 8

• Following primary infection, some viruses lie 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.
• Reactivation of viral replication can occur
• Reactivations may or may not cause apparent disease
• Reactivation more likely to occur and be more severe in immunocompromised.
• Examples:

Herpes Simplex Virus

Varicella Zoster Virus

Question 9

Viruses & Cancer Mechanisms:

Answer 9

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

Question 10

Examples

Answer 10

• EBV: Burkitt’s lymphoma, Hodgkin’s lymphoma, nasopharyngeal carcinoma, post-transplant lymphoproliferative disease
• Human herpes virus 8: Kaposi’s sarcoma, primary effusion lymphoma, Castleman’s disease
• Human T-cell Lymphotropic Virus: Adult T-cell leukaemia/lymphoma
• Human Papillomavirus: cervical, anal, oropharyngeal cancers
• Hepatitis B: hepatocellular carcinoma
• Hepatitis C: hepatocellular carcinoma

Question 11

Detection Methods

Answer 11

• Whole organism- through microscopy and culture
• Part of organism – e.g. antigen, nucleic acid- through DNA/RNA detection,
• Immune response to a pathogen – i.e. antibodies- similar methods as part of organism.

Question 12

Antiviral Therapy

Answer 12

• All antiviral agents are virustatic, none are virucidal
• As viruses utilise host cell enzymes in order to replicate, there are limited viral proteins that are potential targets for antiviral drugs
• Toxicity to the host cell is not uncommon: side effects
• Only used in a minority of viral infections

Question 13

Antivirals may be used for:

Answer 13

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

Question 14

Prevention of Viral Infection

Answer 14

• Immunisation
• Prophylactic treatment post exposure
• Infection prevention & control measures
• Isolation of symptomatic patients
• Personal protective equipment
• Safe use and disposal of sharps
• Blood / tissue / organ screening
• Antenatal screening

Question 15

Eradication

Answer 15

Viruses with the following properties can potentially be eradicated:

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

Question 16

Laboratory medicine

Answer 16

POCT (Point of Care Testing): is laboratory testing performed in the clinical setting by non-laboratory healthcare professionals.

Importance:

• Improved turnaround time
• Potential for better monitoring of certain conditions
• Smaller sample volumes
• Less clinically invasive
• In some out-patient settings, POCT results can be used to adjust patient’s medication resulting in less frequent clinic appointments