Basic introduction to virology

Question 1

Virus classification (Taxonomy)

Answer 1

1. Virus order
2. Virus family
3. Subfamily
4. Type species
5. Morphology
6. Genetic material (DNA or RNA)
7. Envelope

Question 2

Baltimore classification of human viruses

Answer 2

I - dsDNA = double-stranded DNA viruses
II - ssDNA = single-stranded DNA viruses
III - dsRNA = double-stranded RNA viruses
IV - ssRNA(+) = Positive-sense single-stranded RNA viruses
V - ssRNA(-) = Negative-sense single-stranded RNA viruses
VI - ssRNA-RT = RNA reverse-transcribing viruses
VII - dsDNA-RT = DNA reverse-transcribing viruses

Question 3

How to differentiate between bacterial and viral sources of infection?

Answer 3

• It is not easy and it requires medical interventions and elaborate diagnostic procedures
• Both may cause very similar symptoms
• However, some symptoms are pathognomonic
• Secondary bacterial infection-symptoms persist longer than the expected 10 days virus tend to last; fever is higher than in viral infection
• Have to rely on diagnostic tests to differentiate between the two: CRP; FBC differential; BC, PCR, CSF cell count etc;
• Antivirals do not work in bacterial infections and antibacterial medications cannot treat viral infections;

Question 4

What is the purpose of diagnosing viral infection?

Answer 4

1. Medical (therapeutic) patient management
2. Epidemiological (Public health)
3. Intrahospital infection prevention and control
4. Academic

Question 5

What are some virological techniques?

Answer 5

• Nucleic acid-based technologies. e.g. polymerase chain reaction (PCR)
• The next generation sequencing (NGS)
• Monoclonal antibodies
• Enzyme immune assays

Question 6

What are the methods for detecting virus infections?

Answer 6

• Detection of viral antigens
• Detection of nucleic acids (PCR)
• Electron microscopy
• Virus culture
• Histopathology staining
• Serology testing: presence of virus-specific antibodies (IgM and IgG)

Question 7

Enzyme linked immunosorbent assay

Answer 7

• Applied for the detection of:
  1. antibodies against viruses or;
  2. viral antigens;
• Several versions of Enzyme Immunoassays (EIA) are in use for antigen detection;
• “Capture” antibody specific for the viral antigen is bound to the surface of the plastic wells;
• When the sample is added, viral antigen present in the sample binds to the capture antibody;
• When the second antibody is added (with enzyme label)-colour change.

Question 8

What is the detection of viral pathogens dependent on?

Answer 8

1. Obtaining an adequate specimen from the appropriate site
2. Proper timing of specimen collection relative to onset of symptoms
3. Timely processing the sample

Question 9

What is a needlestick injury?

Answer 9

• An incident in which the blood of a patient comes into contact with the blood of a health care worker
• There are three types of exposure in health care settings associated with significant risk from blood or higher risk body fluids:
  1. Percutaneous injury
  2. Exposure of broken skin
  3. Exposure of mucous membranes including eyes and mouth

Question 10

What transmits infection?

Answer 10

-Anything that has blood in it can transmit blood-borne diseases and cause infection.

Question 11

Management of needlestick injuries

Answer 11

• Encourage the wound to bleed, ideally by holding it under running water
• Wash the wound using running water and plenty of soap
• Do not scrub the wound while you’re washing it
• Do not suck the wound
• Dry the wound and cover it with a waterproof plaster or dressing