virology

Question 1

in diagnostic methods, what can we detect?

Answer 1

• infectious virus: virus isolation and EM
• protein components: antigens of the virus
• genetic components: DNA or RNA
• host response: antibody or cell responses

Question 2

what are the different methods of diagnosing?

Answer 2

• cell culture and electron microscopy
• PCR (detects specific sequences of DNA)
• antibody detection
• antigen detection
• quantification of an antibody/antigen
• serotyping
• quantification of genome (viral load)
• genome sequencing

Question 3

what are the limitations of laboratory tests?

Answer 3

• false negative results = sensitivity

- false positive results = specificity

Question 4

define sensitivty

Answer 4

tests ability to correctly identify positive sample

Question 5

define specificity

Answer 5

tests ability to correctly identify negative samples

Question 6

what are the different types of samples used? what method is used to asses it?

Answer 6

• throat swab, NPA, BAL, ET (PCR)
• stools (antigen detection, PCR)
• urine (PCR)
  CSF (PCR)
• clotted blood (serology - antibody detection)
• EDTA blood (PCR/ viral testing load)
• saliva (serology, PCR)

Question 7

which antibody is a marker of recent infection?

Answer 7

• IgM is marker of recent infection
• IgG is created later in host response and lasts longer
• both are created in acute phase of disease

Question 8

what is avidity and what does an antibody avidity test condirm?

Answer 8

• avidity: strength with which antibodies bind to a specific antigen
• confirms a positive IgM result
• early on in infection avidity is low but it gets better over a period of months as antibodies mature

Question 9

why is virus isolation in cell culture rarely used?

Answer 9

• slow
• time consuming
• still used for phenotypic antiretroviral susceptibiltiy testing

Question 10

what is immunofluorescence used for?

Answer 10

• direct detection of viral antigens
• typing and cell culture conformation
• rapid and inexpensive

Question 11

how does PCR work?

Answer 11

1. carry out 30 cycles usually
   - dsDNA is starting block
   - denaturing strands by heating
   - Taq polymerase elongates chain
   - cycles induce exponential expansion