III. A - Virology | 6. Laboratory diagnosis of viral infections

Question 1

I. Basics
1. What are the diagnosis of viral infections?

Answer 1

1. Serology ( ELISA, hemagglutination inhibition test, virus neutralisation, immunoblot,
   rapid tests, Titer)
2. PCR
3. Other methods for detection of viruses: Isolation = cultivation, electron microscopy

Question 2

I. Basics
2. What are the types of antibodies - immunoglobulins

Answer 2

Question 3

I. Basics
3. What is the Kinetics of antibody response?

Answer 3

• Primary exposure to antigen: IgM response first
• Secondary exposure, immune memory: IgG mainly

Question 4

II. Diagnosis of viral infections
1. What are the diagnosis of viral infections?

Answer 4

1. Serology
   - Antigen detection
   - Antibody detection
2. PCR
3. Other methods for detection of viruses: Isolation = cultivation, electron microscopy

Question 5

II. Diagnosis of viral infections - Serology
2A. What are the 2 types of serology?

Answer 5

• Antibody detection from blood: proves that the patient was exposed to the virus
• Antigen detection from sample according to the site of the infection

Question 6

II. Diagnosis of viral infections - Serology
2B. How do we detect antibody?

Answer 6

Question 7

II. Diagnosis of viral infections - Serology
2B. How do we detect antigen?

Answer 7

Question 8

II. Diagnosis of viral infections
3. What are the features of ELISA?

Answer 8

• ELISA = Enzyme-linked immunosorbent assays

Question 9

II. Diagnosis of viral infections
4. What are the types of ELISA?

Answer 9

Question 10

II. Diagnosis of viral infections
5A. What are the features of lateral flow assays/ immunochromatography tests?

Answer 10

Rapid tests
- Eg. Coronavirus antigen tests, C. difficile toxin detection etc.

Question 11

II. Diagnosis of viral infections
5B. How do we perform lateral flow assays/ immunochromatography tests?

Answer 11

• membrane-bound, antigen-specific antibodies
• gold-particle conjugated, antigen specific antibodies in the sample slot
• if the added sample contains the antigen, the antibody-gold particle conjugates bind to it, and start to roll (diffuse) together on the membrane
• membrane-bound antibodies also capture the antibody-gold particle conjugate captured antigens („complexes”)
  ➡ membrane bound antibodies are found in a single line, thus the bound complexes will be enriched in that line ➡local concentration increase of gold particles creates a visible reaction (line)
• a secondary line contains antibodies specific NOT to the antigen, but to the primary, gold-particle conjugated antibody: any time the test is performed (even if the antigen is not present) it will bind to the antibody-gold particle conjugates ➡ proves that the test procedure happened ➡ control line

Question 12

II. Diagnosis of viral infections
6A. What is the purpose of using PCR in Diagnosis of viral infections?

Answer 12

• Detects presence of nucleic acid of the virus
• Detection of copy number= viral load : important in severe infections eg. HIV, HCV

Question 13

II. Diagnosis of viral infections
6B. How do we perform PCR in Diagnosis of viral infections?

Answer 13

1) Heat DNA to separate strands
2) Cool quickly to allow primers to anneal to complementary sequences
3) Heat and add DNA polymerase to synthesize new DNA strands
4) Each time cycle is repeated → target DNA amount is doubled
=> Gel electrophoresis is used for visualization of PCR results (separates fragments according to size)

Question 14

II. Diagnosis of viral infections
7. What are the features of Electron Microscope (EM) for Diagnosis of viral infections?

Answer 14

• Quick, reliable, but expensive
• Good if cultivation not possible