ANSWERS

1. What type of microscope is employed for the examination of viruses and why?
   An electron microscope. Viruses are tiny and it is impossible to view them under a normal light microscope.
2. List 4 characteristics common to all viruses.
   • Obligate parasites.
   • Reproduce by replication and are incapable of reproduction without a host cell.
   • Extremely small in size (20-300nm in diameter).
   • Carry DNA or RNA but never both.
3. What is a virion?
   An inert virus outside of the host; an infectious form which carries genetic material from one cell to another.
4. Name the 2 main parts of a virus which comprise the nucleocapsid.
   • Central core of nucleic acid (DNA or RNA) known as the genome.
   • Protein coat known as the capsid.
     Some viruses also have a lipoprotein membrane forming a surrounding envelope.
5. What is the name of the individual protein structure units which comprise the capsid?
   Capsomeres.
6. List 4 shapes of nucleocapsid.
   • Helical (e.g. distemper).
   • Icosahedral (e.g. parvovirus).
   • Complex (e.g. poxvirus).
   • Composite (e.g. some bacteriophages).
7. List 4 naked virus families.
   • Adenoviridae.
   • Papoviridae.
   • Parvoviridae.
   • Reoviridae.
8. List 4 enveloped virus families.
   • Coronoviridae.
   • Herpetoviridae.
   • Retroviridae.
   • Rhabdoviridae.
9. State the method by which viruses reproduce.
   Replication; the virus invades a susceptible host cell, takes over control of the metabolism and produces copies of itself.
10. Briefly describe the method by which viruses reproduce.
    • Virus attaches to receptor sites on host cell membrane and fuses with it.
    • Virus enters host and capsid breaks down to release nucleic acid.
    • Nucleic acid replicates (either in the host's cytoplasm or nucleus) and directs the host cell metabolism to create new virus material.
    • New virus are assembled and leave the host cell by budding through or rupturing the cell membrane.
11. Why are viral infections difficult to control?
    • Drugs that interfere with viral replication usually have a harmful effect on the host cells.
    • Incubation periods are often lengthy, and thus symptoms may only be seen once large numbers of virus particles have infected a large number of cells.
12. What supportive nursing techniques might you employ in the case of a patient suffering a viral infection?
    • Fluid therapy.
    • Assisted feeding.
    • Antibacterial therapy to limit secondary infection.
13. How might the spread of viral infection be prevented?
    • Barrier nursing.
    • Isolation.
    • Quarantine.
    • Disinfection.
    • Sterilisation.
    • Immunisation.
14. What is a prion?
    A tiny, infectious protein particle responsible for infections within the central nervous system.
15. Give an example of a rare prion disease seen in cats.
    Feline spongiform encephalopathy (FSE).