Virology lab

Question 1

What is it called if a rash has some areas that are raised and some that are flat?

Answer 1

Maculopapular

Question 2

What is a blotchy appearance rash typical of?

Answer 2

Measles

Question 3

If the distribution of a rash is dermatomal, what is this typical of?

Answer 3

Shingles

Question 4

What can virologists detect?

Answer 4

1. Infectious virus
   - virus isolation and electron microscopy
2. Protein components
   - antigens on the virus
3. Genetic components of the virus
   - (DNA or RNA)
4. Host response
   - antibody or cell response

Question 5

Why are cell culture and electron microscopy not used much anymore?

Answer 5

They have been replaced by PCR

Question 6

What is sensitivity?

Answer 6

A test’s ability to correctly identify positive samples

• also called the true positive rate, the recall, or probability of detection[1] in some fields) measures the proportion of actual positives that are correctly identified as such (e.g., the percentage of sick people who are correctly identified as having the condition).
• low rate of false negatives

Question 7

What is specificity?

Answer 7

A test’s ability to correctly identify negative samples

• also called the true negative rate) measures the proportion of actual negatives that are correctly identified as such (e.g., the percentage of healthy people who are correctly identified as not having the condition).
• low rate of false positives

Question 8

What is a marker of recent infection?

Answer 8

IgM

• IgG is created later in the host response and lasts longer
• both are produced in the acute phase of disease but IgG levels only get higher and plateau (lifelong) whilst IgM peaks early and drops after 12 weeks

Question 9

What is essential for diagnosis and monitoring of HIV, HBV and HCV and also for CMV and EBV in immunocompromised?

Answer 9

Viral load- quantification of genomes

Question 10

What typical sort of samples are used by virologists?

Answer 10

1. Throat swab, nasopharyngeal aspirate, bronchoaveolar lavage (BAL)- detection of respiratory viruses by PCR
2. Stools- For rotavirus, adenovirus and norovirus antigen detection or PCR
3. Urine- for BK virus and adenovirus PCR
4. CSF- For herpes viruses and enteroviruses PCR
5. Blood (clotted)- for serology (antibody detection)
6. Blood (EDTA)- For PCR/ viral load testing
7. Saliva- For serology and or PCR e.g measles

Question 11

What is positive IgG with absent IgM consistent with?

Answer 11

Past infection or immunisation

Question 12

What is antibody avidity testing used for?

Answer 12

Confirming a positive IgM result

Question 13

What does antibody avidity mean?

Answer 13

The strength with which antibodies bind to a specific antigen

Question 14

How does antibody avidity change throughout infection?

Answer 14

Early on in course of infection, avidity is low
Then you get maturation of antibody response so avidity gradually increases over a period of 3-6 months
If you have high antibody avidity then it makes it unlikely that infection occured in last 3 months

Question 15

What is virus isolation in cell culture still useful for despite being slow and time consuming?

Answer 15

Phenotypic antiretroviral susceptibility testing

Question 16

What is immunofluorescence still useful for?

Answer 16

Direct detection of viral antigen in clinical samples (e.g. respiratory viruses), can be used for typing and cell culture confirmation
Rapid and inexpensive but subjective and dependent on skill of technician and quality of sample

Question 17

What are the recommended sample types used for investigation of respiratory tract infections?

Answer 17

Throat swab and nose swab
Nasopharyngeal swab
Nasopharyngeal aspirate
Bronchoaveolar lavage
Endotracheal tube secretion

Question 18

What is multiplex PCR?

Answer 18

Where you test for several viruses in one tube rather than single tube for each virus (makes it faster)

Question 19

What are the recommended sample types for CNS disease- meningitis and encephalitis?

Answer 19

1. CSF for PCR (HSV, VZV, enterovirus etc)
2. Stools and throat swab for enterovirus detection (PCR)
3. Blood for serology and or PCR for west nile or japanese encephalitis virus infection and other arboviruses

Question 20

What is PCR?

Answer 20

Polymerase chain reaction- Method for amplifying specific RNA (RT-PCR) or DNA sequences
Cycle (usually 30) of denature, primer annealing and chain elongation

Question 21

What is the starting block for PCR?

Answer 21

dsDNA (if you’re looking for an RNA virus, you need to first make dsDNA copy of RNA using reverse transcriptase)

Question 22

What is the most important enzyme in PCR?

Answer 22

Taq polymerase

-elongates chain

Question 23

What is phylogenetic analysis used for?

Answer 23

Investigating outbreaks

Question 24

What would you see in HIV serology?

Answer 24

antibody and p24 antigen

Question 25

In the serology of which diseases would you see IgG and IgM?

Answer 25

1. Hep A
2. CMV and EBV
3. MMR
4. Parvorius B19

Question 26

What would you see in VZV serology?

Answer 26

IgG

Question 27

What would you see in HBV serology?

Answer 27

surface Ag/Ab, eAg/eAb, core Ab, core IgM

Question 28

What are some methods of diagnosing?

Answer 28

1. PCR
2. Antibody detection -seroloy (EIA= enzyme immunoassay)
3. Antigen detection -serology- (EIA, IF= immunofluorescence)
4. Serotyping
5. Genome sequencing
6. Cell culture and microscopy