An Introduction to Viruses Flashcards
Explain the basic classification and characterisation of viruses.
Viruses are classified according to the following:
- Presence/absence of lipid envelope
- Virion shape/symmetry
- Structure and replication of genome nucleic acid
Outline the principles of viral culture.
Since viruses require (host) cells to thrive/replicate, all cultures must take place in:
- Cell lines
- Tissues
- Intact animals
The cells are grown in a nutrient containing medium at 5% CO2 levels
Describe examples of human virus infections of major importance
Respiratory:
- Influenza A Virus
- Rhinovirus
- Respiratory Syncytial Virus
Gastrointestinal:
- Rotavirus (common cause of diarrhoea)
Neurological:
- Enterovirus
- Herpes Simplex Virus
Tumours:
- Papillomavirus
- Retrovirus (use reverse transcriptase)
Describe the structure of viruses.
- Small (20 - 400 nm in diameter)
- Needs a host cell to replicate
- Have a SPECEFIC host range
There are 3 physical structure types:
- Helical (Protein capsid bind around nucleic acid in a helical fashion)
- Icosahedral (20 faces, each an equilateral triangle)
- Complex (Neither helical nor icosahedral
Explain the concept of host range in relation to viruses.
This relates to specificity in viral infection.
For example some viruses may only infect humans (e.g smallpox and measles) while some may only infect other animals
Describe the consequences of viral infection
Clearance of virus (with no short or long term immunity)
Describe the consequences of viral infection
Clearance of virus (with no short or long term immunity)
Chronic infection (HIV, Hep B and Hep C)
Latent infection
Transformation (altered cellular gene expression)
Explain the concept of viral latency
Some viruses lie dormant in the cell following the primary infection.
Therefore the full viral genome is retained in the host cell, buts its expression is restricted so that few viral antigen and not viral particles are produced.
Examples include:
Herpes Simplex Virus
Varicella Zoster Virus
Describe the link between viruses and cancer and explain the mechanisms through which this results.
Many viral infections can lead to cancer
Mechanisms for cancer caused by viruses include:
- Modulation of cell cycle control (driving proliferation of the cell)
- Modulation of apoptosis (prevention of cell death)
- Reactive oxygen species mediated damage
Describe the indications for and principles of anti-viral therapy.
Detection:
Whole organism
Part of an organism
Immune response to pathogen
Principles:
All antiviral agents are virustatic (inhibit virus growth and development) - due to limitation in viral proteins that can be used as potential targets for antiviral drug
There are large side effects when using antivirals, therefore they are only utilised in the minority of viral infections.
Virus cells grow in a nutrient containing what % of CO2?
5%
When may antivirals be used?
Prophylaxis (preventing disease/infection)
Overt Disease
Pre-emptive therapy (when there is evidence of infection/replication yet still no symptoms)
Suppressive therapy (attempting to keep viral replication below the rate that causes tissue damage in am asymptomatic patient
Describe how to prevent viral infections
- Vaccination (active immunisation)
- Passive immunisation with immunoglobulin/antibodies
- Prophylactic treatment post exposure (preventative treatment)
- Screening of blood/tissue/organ
- Antenatal screening (before birth screening)
Explain how viruses can be eradicated.
Eradication is possible if:
- 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
