Viruses Flashcards
What are viruses?
Viruses are a small non-cellular genetic element that cannot replicate outside of a host cell.
What is the structure of viruses?
Icosahedral (20 faces; equilateral triangles)
Helical (protein binds around DNA/RNA in a helical fashion
Complex (neither icosahedral or helical)
What pathogens do viruses obligate?
Intracellular- can only act within a cell
Are viruses specific?
Yes- most viruses have a specific host range and can only act within a specific host cell.
What is the study of viruses called?
Virology
What is a virion?
An extracellular form of a virus (exists outside of the host cell and facilitates transmission from one host cell to another, contains nucleic acid genome surrounded by a protein coat, and sometimes other layers of materials).
How are viruses taxonomically classified?
Viruses can be classified according to virion shape/symmetry, the presence or absence of an envelope, genome structure, and the mode of replication.
How do viruses replicate?
A virion is required for transmission between one host cell to another.
(basically, wrapping it in a protein coating: a capsid) The capsid is the infective form. You can also sometimes get a lipid coating derived from the host cell.
What are the methods of viral transmission?
Blood-borne, sexual, vertical (period before and after birth), faecal-oral, droplet, airborne, close contact, vector-borne, or zoonotic (animals).
What is the host range of a virus?
Some viruses may only affect humans (e.g. smallpox/measles).
However, some may also affect animals and birds. This novel virus can be transmitted from animal/bird to a human.
What can confection of an animal/bird viral strain lead to?
Coinfection of animal/bird strains in one organism can lead to recombination and the generation of a new strain.
What are the consequences of viral infection?
- Clearance of virus- with no, short-term or long-term immunity (Hepatitis C no lasting, measles long term)
- Chronic infection- HIV, hepatitis B/C
- Latent infection- Herpes virus
- Transformation- long-term infection with altered cellular gene expression (HPV, Epstein-Barr virus)
What is viral latency?
Following primary infection, some viruses can lie dormant in the cell. The full viral genome is retained in the host cell, but its expression is restricted such that few viral antigens or viral particles are produced.
Reactivation of the viral replication can occur, with reactivations sometimes causing apparent disease and sometimes not.
Who is more susceptible to reactivation of a latent virus?
Those who are immunocompromised (e.g. the elderly)
What mechanisms can allow viruses to develop into 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.
