Introduction to Viruses Flashcards
What size are viruses?
Small, from 20-400 nm in diameter
Viruses are non-cellular.
What does this mean?
Genetic element that cannot replicate independently of a living (host) cell
Name the three structures a virus could have.
Icosahedral, Helical or Complex.
Describe the Icosahedral structure of a virus.
20 faces, each an equilateral triangle
Describe the helical structure of a virus?
Protein binds around DNA/RNA in a helical fashion
Describe the complex structure of a virus.
Simple- just neither helical or icosahedral.
Where do viruses replicate?
Only replicate inside a host cell.
What types of cells do viruses infect?
Most viruses have a specific host range and only infect specific host cell types.
What is the study of viruses?
Virology
Define virion.
Extracellular form of a virus.
Where does a virion exist?
Exists outside host and facilitates transmission from one host cell to another
What do virions contain?
Contains nucleic acid genome surrounded by a protein coat and, in some cases, other layers of material
List the ways a virus family can be classified.
According to-
-Virion shape / symmetry
-Presence / absence of envelope
-Genome structure
-Mode of replication
Name the four ways a virus can be classified regarding taxonomy.
Order, family, genus and species.
Describe the structure of a virion.
Basically-
Nucleic acid is enclosed in a protein capsid which is then enclosed in a lipid envelope.
There are spike projections covering the virion.
How do viruses replicate?
- Viruses attaches to cell wall.
- Virus becomes uncoated so leaves it’s outside.
- Protein capsid and nucleic acid enter the host cell to allow replication of the nucleic acid.
4.Protein synthesis occurs. - Genomic nucleic acid synthase and newly synthesised virus proteins get assembled to produce the new virion.
- New virion is released to go and infect another cell.
->this wasn’t explained v well tbh did the best i could
List a few of the many ways transmission can take place.
Give examples
Blood borne (HIV, Hep b)
Sexually transmitted (HIV, Hep b)
Vertically transmitted (HIV, Hep b)
Droplet (influenza)
Air borne. (measles, chickenpox).
Name some viruses which only effect humans.
Smallpox or measles.
Name a virus which can affect the respiratory syndrome.
Influenza.
Give an example of a virus which can affect the neurological syndrome.
Polio
There are many consequences of viral infection.
Name four consequences.
- Clearance of virus
- Chronic infection
- Latent infection
- Transformation
Give an example of a virus which as the following consequence-
Clearance of virus.
Measles- long term immuinity.
Give an example of a virus which as the following consequence-
Chronic infection.
HIV, Hepatitis B or C
Give an example of a virus which as the following consequence-
Latent infection.
Herpes
Give an example of a virus which as the following consequence-
Transformation
Epstein-Barr Virus, Human Papillomavirus
Describe viral latency.
Some viruses lay dormant in the body following primary infection.
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.
If tested, the virus will not be detected.
What can happen to viruses undergoing viral latency?
Reactivation of viral replication can occur
Reactivations may or may not cause apparent disease
Reactivation more likely to occur and more severe in immunocompromised hosts
Give two examples of viruses which undergo viral latency.
Herpes Simplex Virus
Varicella Zoster Virus- chickenpox
Reactibation of Varicella Zoster Virus- (chickenpox) can lead to what?
Shingles.
Some viruses can lead to serious conditions uch as?
Cancer but other processes are often required too.
Describe some mechanisms which may cause cancer.
- Modulation 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)
How can we detect viruses?
- Whole organisms
- Part of organism e.g. antigen or nucleic acid
- Immune reponse to an antigen using antibodies.
Give an example of a virus that can lead to cancer
Human Papillomavirus (HPV): cervical, anal, oropharyngeal cancers
Name the two ways of looking at the virus organism as a whole.
Using microscopy or culturing.
Explain how we can look at part of an organism in order to detect a virus.
DNA/RNA detection by extraction of genetic material from a sample
Amplification of region of target organism genome (if organism present in sample)
Explain how immune response may allow us to detect a virus.
May be used to determine:
Acute / recent infection
Prior infection / response to vaccination
What does virostatic mean?
Drug which inhibits viral replication
What is a virucide?
A virucide is any physical or chemical agent that deactivates or destroys viruses.
Are antiviral agents virostatic or virucidal?
All antiviral agents are virustatic, none are virucidal
What are antivirals used for?
- Prophylaxis (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)
How is viral infection prevented?
- Vaccinations /immunisations
- Prophylactic treatment post exposure
- Infection prevention and control measures
- Blood/tissue/organ screening
- Antenatal screening
If immediate protection, what can be done?
Passive immunisation with immunoglobulin
List the ways a virus can 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
Name sa virus that has already been eradicated.
Smallpox.
