Diagnosis of Viral Infections

Question 1

ANTIGEN DETECTION:
What are Viral antigens looked for in?

What has this method been replaced by? Why?

1. Direct Immunofluorescence - How is it carried out?
2. Immunochromatographic Methods - What is it commonly used for the diagnosis of?
3. Enzyme-Linked Immunosorbent Assay (ELISA) - Explain in 3 steps how this is carried out?

Answer 1

• Nasopharyngeal aspirates, Blood, Vesicle fluid, Faeces
• NAATs due to improved test performance
  1. Antigens from infected host cells are bound to a slide, and mixed with specific fluorochrome-tagged Antibodies
  2. Dengue

3. • Plate coated with a capture Antibody, and the Sample is added for any Antigens present to bind to the Antibody
   • Enzyme-conjugated Primary Antibody is then added to bind to the detecting Antigen - Forms a “Sandwich”
   • Substrate added and converted by the enzyme to its detectable form - Produces a visible colour change

Question 2

ANTIBODY DETECTION:
When are IgM’s and IgG’s produced after a viral infection?
→ What does detection of IgM therefore indicate?

Serology:
Which type of organisms is it used for?

What is it used for?

How is Serum produced from Blood?
→ What does Serum contain?

1. What will be the result if they have No Past/Current infection or Immunisation?
2. What will be the result if they’ve had an Acute/Recent infection?
3. What will be the result if they’ve had a Resolved infection or Immunisation?

Answer 2

• IgM produced and lasts around 1-3 months before declining, while IgG starts to be produced
  → Recent infection (1-3 months) or Seroconversion (Previous negative test for Ig, then presence of Ig later)
• ELISA
• Those difficult to culture
• • Detect Antibody response in symptomatic patients
  • Determine if vaccination worked
  • Directly look for antigens produced by pathogens
• Blood is coagulated with micronized silica particles, and a gel is used to trap its cellular components
  → Proteins, Antigens, Antibodies, Electrolytes and some drugs

1. Negative IgM and IgG
2. Positive IgM and Negative/Positive IgG
3. Negative IgM and Positive IgG

Question 3

NUCLEIC ACID AMPLIFICATION TESTS (NAATS):
What does it detect? What is it amplified by?

What method can be used to detect several targets in one sample?

What are the Advantages of NAATs?

What are the Limitations of NAATs?

Answer 3

• RNA, DNA - Amplified by PCR
• Multiple Fluorescent probes
• Automated, Very sensitive and specific, Rapid, Useful for detecting viruses for a diagnosis, Useful for monitoring treatment response
• Detects viruses that aren’t causing the infection, Very sensitive (can cause contamination), Need to know which virus to look for so the right primers and probes are added

Question 4

Genotype Sequencing:
What is it used to predict?

When would it be used?

Answer 4

• Response to Antivirals

- In new patients or if there are signs of drug resistance