Virology Flashcards
What can we detect in diagnostic virology? (x4)
□ 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.
What techniques are used for antigen detection?
Immunofluorescence and enzyme immunoassay (EIA).
What technique is used for antibody detection?
Serology – identification of antibodies in serum.
What technique is used for genome detection?
Polymerase chain reaction – PCR.
What are the two types of tests for genetic components in diagnostic virology?
QUALITATIVE: presence of absence of DNA/RNA; QUANTITATIVE: the amount of the DNA/RNA present to determine VIRAL LOAD.
How common are each of the diagnostic methods in virology?
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.
What are the limitations of any laboratory test? (x2)
□ 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.
What typical samples are sent for virological diagnosis? What diseases may be diagnosed from the samples, and how we test the samples? (x7) !!!!!
□ 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.
What antibodies are studied in serology? (x2) Why are they useful?
□ 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.
What is a limitation of measuring IgM antibodies in serology? What test is used to overcome this?
□ 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.
How is HIV serology carried out?
□ 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.
What does specific and non-specific reactivity refer to diagnostics?
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.
What is virus isolation in cell culture used for?
Rarely used. However, used for phenotypic antiviral susceptibility testing (e.g. used in herpes simplex virus) – used to test for and predict resistance.
What are the disadvantages of virus isolation in cell culture?
Slow, expensive and time-consuming. Not very sensitive/specific.
What is electron microscopy used for in viral diagnostics?
Visualise viruses in stool and vesicle fluid samples but it is rarely used.
What is immunofluorescence used for?
Occasionally used to directly detect antigens in clinical samples.
What are the advantages and disadvantages of immunofluorescence that now warrant its rare use?
Rapid and inexpensive, but subjective and relies on skill and sample quality.
How is PCR done?
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.
What is multiplex PCR?
Testing for several viruses in one tube.
What is genome sequencing used for in virology? (x3)
□ 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).
What is the characteristic symptom of shingles?
Rash will present within a specific dermatome.
What is a vesicular rash?
Presence of vesicles at the level of the skin that can have different sizes. They are round and filled with liquid.
What may cause vesicular rash?
HSV, VZV (causes primary, latent and recurrent infection (chickenpox, latent period, shingles)) and enterovirus.
What is a maculopapular rash?
Characterised by a flat, red area on the skin that is covered with small merging bumps.
What may cause maculopapular rash?
Measles, rubella, parvovirus.
