Viruses

Question 1

Virus, size and 3 structures

Answer 1

• Small 20-400nm
• Non-cellular
• Icosahedral (20 faces)
• Helical: protein binds around DNA/RNA in a helical fashion
• Complex: neither icosahedral or helical

Question 2

Define obligate intracellular pathogens

Answer 2

• Need a host to survive
• Can only replicate inside host cell
• Need a specific host range and only infect host cell types

Question 3

Taxonomy of viruses

Answer 3

Order
Family
Genus
Species

Question 4

Classification of virus families

Answer 4

Virion shape/symmetry
Presence/absence of envelope
Genome Structure
Mode of replication

Question 5

Blood-borne viruses

Answer 5

HIV
Hep B
Hep C

Question 6

Sexually transmitted virsuses

Answer 6

HIV
Hep B
Hep C increasingly

Question 7

Vertically transmitted viruses

Answer 7

HIV

Hep B

Question 8

Faecal-oral route viruses

Answer 8

Hep A
Hep E
Polio

Question 9

Droplet viruses example and definition

Answer 9

• Large particles and fall within a short distance of a person
• Influenza, Respirtory Syncytial Virus

Question 10

Airborne example and definition

Answer 10

• Aerosolised, can travel much further in the environmment
• Measles
• Chickenpox

Question 11

Close contact transmitted viruses

Answer 11

Herpes simplex
CMV (Cytomegalovirus)
EBV - Glandular fever

Question 12

Vector-borne viruses

Answer 12

Dengue
Yellow fever
Chikungunya

Question 13

Zoonotic viruses

Answer 13

Rabies
MERS
Ebola

Question 14

Host range

Answer 14

Some viruses may only infect humans e.g. smallpox, measles
Some may also infect other animals which can result in transmission of a novel virus to humans or coninfection where human and animal strains may recombine to generate a new strain

Question 15

Consequences of viral infections

Answer 15

• Clearance (with no, short or long term immunity)
• Chronic infection
• Latent infection
• Transformation (long term infection with altered cellular gene expression)

Question 16

Latent infection life cycle

Answer 16

• How you get cold sores or shingles
• Virus lies dormant after 1ary infection
• Full viral genome is retained in the host cell but it’s expression is restricted, a few viral antigens and no viral particles are produced
• Reactivation of viral replication can occur
• More likely to occur and more severe in immunocompromised

Question 17

Viruses and cancer, mechanisms

Answer 17

• Viruses can lead to cancer but often need another event to also occur
  Mechanisms:
• Modulation of cell cycle control, drives cell proliferation
• Modulation of apoptosis, prevention of programmed cell death
• Reactive oxygen species mediated damage, some viral infections cause inflammatory processes which lead to cancer via reactive oxygen species

Question 18

Viruses and cancer examples

Answer 18

EBV - Glandular fever:
Burkitt’s lymphoma, Hodgkin’s lymphoma, nasopharyngeal carcinoma
Human herpes virus: Kaposi’s sarcoma, primary effusion lymphoma
Human T-cell Lymphotropic virus: Adult T-cell leukaemia/lymphoma
Human Papillomavirus: cervical, anus, oropharyngeal cancers
Hepatitis B and C: hepatocellular carcinoma

Question 19

Principles of viral culture

Answer 19

You can either detect the whole organism or part of the organism

Question 20

Whole organism detection method

Answer 20

• Electron microscopy, see the shape and match it
• Culture
  but neither are really done anymore

Question 21

Part of organism detection method

Answer 21

• Antigen detection: you have a specimen coated in antibodies and you look for a reaction with fluoresence
• DNA/RNA detection
• Extraction of genetic material from sample
• Amplification of region of target organism genome: PCR, look for amplification curve that matches the virus
• Immune response to pathogen: look for a sign that they’ve been exposed, opposite of antibody test. Can determine acute/recent infection or prior infection/response to vaccination

Question 22

Antiviral therapy

Answer 22

• All antiviral agents are virustatic
• 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 an uncommon side effect
• Only used in the minority of viral infections as there aren’t many available

Question 23

When you might use an antiviral

Answer 23

• Prophylaxis (preventing infection)
• Pre-emptive therapy, if there’s evidence of infection, replication but no apparent symptoms. Especially in HIV
• Overt disease
• Suppressive therapy, keep viral replication rate low to prevent tissue damage

Question 24

Prevention of viral infection

Answer 24

• Immunisation: vaccination, passive immunisation with immunoglobulin
• Prophylactic treatment post exposure
• Infection prevention and control measures. Isolate symptomatic patients, PPE, safe use and disposal of sharps
• Blood/tissue/organ screening
• Antenatal screening

Question 25

What do you need to eradicate a virus?

Answer 25

- 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 and social support