Introduction to Viruse Flashcards
What is the basic outline of the organism and host?
Exposure leads to infection which then leads to clinical symptoms.
Host response can make the symptoms worse.
Name some viral factors
Natural history/life cycle Mode and efficiency of transmission Tropism Invasivness Opportunism Virulence
Name some host factors
Age Genetic predisposition Immune status Specific immunity Trauma/surgery/foreign body
What are some sources of exposure to viruses?
Social Food/water Environmental Occupational Hospital Sexual Drugs Travel Animals Maternal
Ultimately the type of exposure is orally (mucosal membranes in mouth), respiratory or percutaneous (skin).
What is the basic viral structure?
DNA or RNA
Caspid core (protects genetic material)
Polymerase protein (enzyme packaged with the virus)
Envelope possibly
What are some distinguishing characteristics of viruses?
They are obligate intracellular parasites.
Viruses contain either DNA or RNA genomes compromised of genetic material encoding structural or functional proteins. Structural genes encode the capsids and the polymerase proteins or glycoproteins sticking out of enveloped proteins. Functional proteins (enzymes) - the smaller the genome, the fewer of these. Smaller genome viruses rely on host cell.
New versus are formed by assembly of components synthesised using host cell proteins. They enter a cell and release genetic material. This material undergoes transcription and then assembly of this protein to make capsins. Eventual release of virus from cell.
How do we characterise viruses into families?
- Type of nucleic acid (DNA or RNA)
- Symmetry of nucleocaspid
- Lipid envelope
- Number of strands of nucleic acid & their physical construction
- Polarity of viral genome (positive or single stranded RNA)
Give some details on the stature of the caspid
Caspids are constructed from a smaller number of virally-encoded protein subunits called capsomeres.
The viral genome enclosed by the caspid coat is called nucleocaspid.
Virus particles show 3 types of symmetry:
- Icosahedral
- Helical
- Complex
Explain the isosahderal caspid
A caspid composed of 20 solid equilateral triangles arranged around the face of the sphere.
The simplest icosahedral caspid is made by 3 identical subunits to form each face, so the minimum number of subunits is 60 (2x3).
The structural units may be composed of more than one viral protein.
What is the structure of the helical caspid?
Cashmeres are bound in a periodic fashion to the viral genome, thus winding the genome into a helix/
Only occurs in RNA viruses.
Explain the complex caspid structure
Neither purely helical or icosahedral.
Poxviruses are the only human viruses with this symmetry.
The nucelocaspid is a continuous cylinder surrounded by a lipid layer and complex proteinaceous core wall (pallisade layer).
What is the importance of viral surface proteins?
They attach to membrane proteins (Receptors) in host cell - determinants of tropism.
Target for antibodies - neutralisation.
Determinants of antibody specificity (Serotype)
What is the basic structure of a viral envelope?
Lipid bilayer derived from the host cell membrane.
Contains viral glycoproteins form the host cell membrane.
Not present in all viruses.
What does the presence or absence of the envelope determine?
ability to survive outside cell and the mode of transmission
non-enveloped viruses are able in the environment - may be transmitted by food or water
e.g. noroviruses
enveloped viruses do not perish long in the external environment - they are spread by close or intimate contact
e.g. influenza, HIV, Hep B
How do viruses replace and spread within host?
- Attachment of virus
- Entry of virus
- Uncoating of virus
- Production of viral proteins
- Replication of viral genome
- Assembly at cell surface membrane
- Release of virus
