Viruses mw % + Flashcards Preview

ME2308 Principles of Disease > Viruses mw % + > Flashcards

Flashcards in Viruses mw % + Deck (16)
Loading flashcards...

Virus Basics 

  • 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)


 Virus families classification (4)

Can be classified according to:

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


Virion Structure pic


Virus Replication pic►


Transmission pic 


Host Range

  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


Consequences of viral infection

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


Viral Latency

  •  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


Viruses & Cancer Mechanisms:

  • 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)



  • 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


Detection Methods

•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.


Antiviral Therapy

• 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


Antivirals may be used for:

  • 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)


Prevention of Viral Infection


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



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


Laboratory medicine

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


•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