Virology Flashcards

1
Q

What can we detect in diagnostic virology? (x4)

A

□ LOOK FOR THE VIRUS ITSELF: Involves growing and isolating the infectious virus in culture and studying it with electron microscopy. □ PROTEIN COMPONENTS – ANTIGENS: in the serum or CSF. □ GENETIC COMPONENTS: of the virus (DNA or RNA). □ LOOK FOR HOST RESPONSE: e.g. test for antibody or cell responses.

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2
Q

What techniques are used for antigen detection?

A

Immunofluorescence and enzyme immunoassay (EIA).

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3
Q

What technique is used for antibody detection?

A

Serology – identification of antibodies in serum.

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4
Q

What technique is used for genome detection?

A

Polymerase chain reaction – PCR.

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5
Q

What are the two types of tests for genetic components in diagnostic virology?

A

QUALITATIVE: presence of absence of DNA/RNA; QUANTITATIVE: the amount of the DNA/RNA present to determine VIRAL LOAD.

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6
Q

How common are each of the diagnostic methods in virology?

A

Rarely do we study the actual virus using cell culture and electron microscopy. Now, in virology, diagnostics is focused more towards serology (antibody detection – this is the main test), antigen detection and genome detection.

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7
Q

What are the limitations of any laboratory test? (x2)

A

□ SENSITIVITY: the test’s ability to correctly identify positive samples i.e. few false negatives. □ SPECIFICITY: the test’s ability to correctly identify negative samples i.e. few false positives.

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8
Q

What typical samples are sent for virological diagnosis? What diseases may be diagnosed from the samples, and how we test the samples? (x7) !!!!!

A

□ Throat swap, nasopharyngeal aspirate (NPA – nose swab), bronchoalveolar lavage (BAL – bronchoalveolar washing), ET secretions (suctioning tracheal secretions): for detection of respiratory viruses by IMMUNOFLUORESCENCE or PCR. □ Stools: for rotavirus, adenovirus, norovirus by EIA or PCR. □ Urine: for BK virus and adenovirus by PCR. □ CSF: for herpes simplex virus (HSV), meningitis and enterovirus by PCR. □ Blood (clotted): for HIV, Hepatitis, HBV, HCV, MMR by SEROLOGY (antibody detection) – remember, serology is the main virology diagnostic tool. □ Blood (EDTA): prevents coagulation; used to measure VIRAL LOAD by PCR. □ Saliva: for measles by SEROLOGY or PCR.

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9
Q

What antibodies are studied in serology? (x2) Why are they useful?

A

□ IgM antibodies produced in the first three months i.e. acute phase of disease.

□ IgG antibodies produced by the body long-term and are present in the blood for life.

□ Useful because you can date the disease.

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10
Q

What is a limitation of measuring IgM antibodies in serology? What test is used to overcome this?

A

□ IgM tests are very non-specific. In other words, they are very sensitive, but not specific meaning that they often produce FALSE POSITIVES. □ Therefore, ANTIBODY AVIDITY TESTS are used as a follow-up test. □ IgM avidity (strength of antibody binding to antigen) is measured. IgM avidity increases over 3-months, so if antibody avidity is high, then it is unlikely the infection occurred within the past three months. □ Can also be used to date the virus.

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11
Q

How is HIV serology carried out?

A

□ EIA used to look for antibody AND antigen. This makes the test very sensitive and allows for early detection where antigen is present, but body hasn’t yet started producing antibodies. □ All reactive samples undergo confirmatory testing in a second assay to exclude non-specific reactivity (false positives). □ Confirmed positives undergo typing to test for HIV 1 or 2. □ Then there is a repeat blood sample and EDTA blood is used for a measure of the viral load.

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12
Q

What does specific and non-specific reactivity refer to diagnostics?

A

Specific reactivity indicates true positive; non-specific reactivity indicates false positive. Don’t actually know if this is true – it is my best guess. Cannot seem to find actual definitions online.

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13
Q

What is virus isolation in cell culture used for?

A

Rarely used. However, used for phenotypic antiviral susceptibility testing (e.g. used in herpes simplex virus) – used to test for and predict resistance.

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14
Q

What are the disadvantages of virus isolation in cell culture?

A

Slow, expensive and time-consuming. Not very sensitive/specific.

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15
Q

What is electron microscopy used for in viral diagnostics?

A

Visualise viruses in stool and vesicle fluid samples but it is rarely used.

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16
Q

What is immunofluorescence used for?

A

Occasionally used to directly detect antigens in clinical samples.

17
Q

What are the advantages and disadvantages of immunofluorescence that now warrant its rare use?

A

Rapid and inexpensive, but subjective and relies on skill and sample quality.

18
Q

How is PCR done?

A

Polymerase chain reaction to amplify specific RNA/DNA. 1. Denature DNA at 95 degrees. 2. Anneal primers by cooling to 55 degrees. Primers are a complementary sequence to the target DNA region. 3. Elongate chain using Taq polymerase, heating to 72 degrees. 4. Process is repeated. 5. Sample is usually studied using electrophoresis.

19
Q

What is multiplex PCR?

A

Testing for several viruses in one tube.

20
Q

What is genome sequencing used for in virology? (x3)

A

□ Genotyping – studying differences in the genome of viruses, so can be used to diagnose the type of virus a patient has e.g. enteroviruses – there are many types. □ Antiviral resistance testing. □ Phylogenetic analysis (evolutionary development of viruses).

21
Q

What is the characteristic symptom of shingles?

A

Rash will present within a specific dermatome.

22
Q

What is a vesicular rash?

A

Presence of vesicles at the level of the skin that can have different sizes. They are round and filled with liquid.

23
Q

What may cause vesicular rash?

A

HSV, VZV (causes primary, latent and recurrent infection (chickenpox, latent period, shingles)) and enterovirus.

24
Q

What is a maculopapular rash?

A

Characterised by a flat, red area on the skin that is covered with small merging bumps.

25
Q

What may cause maculopapular rash?

A

Measles, rubella, parvovirus.