Diagnostic Virology

Question 1

What is a maculopapular rash?

Answer 1

Some areas are raised and some areas are flat. This blotchy appearance is typical of measles rash

Question 2

What is a dermatomal distribution of a rash indicative of?

Answer 2

Shingles

Question 3

What components of the virus can be used in virus detection?

Answer 3

Infectious Virus

• Virus isolation and electron microscopy

Protein Components (antigens) on the virus

• E.g. p24 antigen in HIV, surface antigen in HBV etc

Genetic Componentsof the virus (DNA or RNA)

• Quantitative or qualitative tests are available

The Host Response

• E.g. antibody or cell responses

Question 4

What is the main method of virus detection?

Answer 4

PCR

PCR is a sensitive method used to detect specific sequences of nucleic acids

Question 5

What technique is used for antibody detection?

Answer 5

Enzyme immunoassay – detects antibodies and antigens

Question 6

Define sensitivity.

Answer 6

Low rate of false negatives.

Sensitivity= the test’s ability to correctly identify positive samples

Question 7

Define specificity.

Answer 7

Low rate of false positives.

Specificity= the test’s ability to correctly identify negative samples

Question 8

What does quantification of the genomes allow assessment of?

Answer 8

Viral load

• This is essential for diagnosis and monitoring of HIV, HBV and HCV, and also for CMV and EBV in the immunocompromised

Question 9

What is the difference between IgM and IgG in terms of when their levels rise following infection?

Answer 9

IgM is a marker of RECENT infection

IgG rises later on

Question 10

What does positive IgG and absent IgM indicate?

Answer 10

Past infection or immunisation

Question 11

What is targeted in the detection of HIV?

Answer 11

Antibody and p24 antigen

Question 12

What other investigations are performed on people who are identified as HIV positive?

Answer 12

Typing (HIV 1 or HIV2) Repeat blood sample and EDTA blood for HIV viral load (for genotyping and baseline resistance testing)

Question 13

What test is used to confirm a positive IgM result?

Answer 13

Antibody avidity testing

Question 14

Describe how antibody avidity changes in infection.

Answer 14

Early on in the infection, avidity is LOW Then you get maturation of the antibody response so the avidity will increase over a period of 3-6 months If you have HIGH antibody avidity, then it is unlikely that the infection occurred in the last 3 months

Question 15

What is immunofluorescence useful for?

Answer 15

• Direct detection of viral antigens in clinical samples (e.g. respiratory viruses)
• Can be used for typing and cell culture confirmation
• Rapid and inexpensive but subjective and very dependent on the skill of the technician and the quality of the sample
• oThe lungs are hyperinflated oNormally you should only be able to count 6 ribs but here you see 7 anteriorly so it is hyperinflated , bronchitis

Question 16

What is the term given to the method of PCR that allows testing for more than one virus using a single test tube?

Answer 16

Multiplex PCR

Question 17

What is sampled when testing for meningitis/encephalitis?

Answer 17

• CSF for PCR (HSV, VZV, enterovirus etc.)
• Stools and Throat Swab for enterovirus detection (i.e. by PCR)
• Blood for serology and/or PCR for West Nile and/or Japanese Encephalitis virus infection and other arboviruses
• NOTE: if there is some travel history you would also look for more exotic viruses

Question 18

What is sampled when testing for causes of diarrhoea/vomiting?

Answer 18

Stool (and vomit)

Question 19

What must happen first before PCR is performed to identify the genome of an RNA virus?

Answer 19

The RNA must be reverse transcribed by reverse transcriptase to dsDNA

dsDNA is the start point of PCR

Question 20

Describe the process of PCR.

Answer 20

The dsDNA is denatured by heating it The primers then bind to the single stranded DNA and Taq polymerase joins complementary nucleotides to the template strand

Question 21

What are the applications of sequencing viral genomes?

Answer 21

We can also sequence viral genomes •In addition to genotyping we can do antiviral resistance testing•This is vital for selecting the correct antiretroviral drugs •Phylogenetic Analysis-­‐this is a tool for investigating outbreaks