diagnosis of viral infections

Question 1

tests we can do to diagnose viral infection

Answer 1

Electron microscopy, Virus isolation (doing a cell culture), Antigen detection, Antibody detection, nucleic acid amplification, sequencing for genotype and to detect antiviral resistance

Question 2

what classes of microbes can we see in light microscopy

Answer 2

bacteria, fungi, protozoa helminths

viruses cannot be seen - so small they need electron microscopy

Question 3

how does electron microscopy work

Answer 3

fire a beam e- that scatter when they pass through thin sections of a specimen, e- that do not scatter (are transmitted) and used to generate an image. darker regions scatter more/are denser.

Question 4

define cytopathic effect

Answer 4

structural changes in host cells that are caused by viral invasion

Question 5

how do viruses appear in cell culture

Answer 5

viruses require host cells to replicate .’.cause cytopathic effect .’. if viral infection host cels have altered appearance e.g. shrink/swell

Question 6

why do we no longer use viruses in cell culture to diagnose

Answer 6

is a slow process, some viruses do not grow in cell culture, can become contaminated

Question 7

how may we detect viral antigens

Answer 7

direct immunoflourescence, enzyme immunoassay, immunochromatographic methods

Question 8

how to use immunofluorescence for antigen defection

Answer 8

get viral antigen from infected cells from patient. then add specific antibody (tagged with fluorescent tag) and mix with same, if match, antibody will bind the viral antigens and can see this using a microscope under UV

Question 9

how to use Elisa for antigen detection

Answer 9

a plate is coated with a ‘capture antibody’. patient sample is added. complementary antigen present will bind to the capture antibody. then add another load of antibodies conjugated with enzyme - specific to antigen. when bound, enzyme activated., then add enzyme substate, enzymatic activity = visible colour change.

Question 10

what is immunochromatography

Answer 10

devices intended to detect the presence (or absence) of a target analyte in sample (matrix) without the need for specialized and costly equipment

Question 11

how to use immunochromatography for antigen detection

Answer 11

when infected, humoral immune system activated = IgM produced, present for 1-3 months. As IgM declines, IgG produced and [IgG] rises. use serology to detect Ig

Question 12

what is serology to detect virus infection

Answer 12

indirect detection of the pathogen via looking for antibodies. can use serology to: detect antibody response in symptomatic patients, determine if vaccine is successful, directly look for antigen produced by pathogens

Question 13

serology; no IgM or IgG

Answer 13

no past or current infection or immunisation

Question 14

serology; IgM but no IgG

Answer 14

acute/recent infection

Question 15

serology; no IgM but IgG

Answer 15

resolved infection or successful immunisation

Question 16

what are molecular diagnostic tests

Answer 16

Nucleic acid amplification (NAATs) main method here being PCR but are others. used to detect viral RNA or DNA

Question 17

why are NAATS used commonly in diagnosis

Answer 17

bc can be automated, highly sensitive, are specific, can generate huge numbers of amplicons

Question 18

clinically when do we use NAATS

Answer 18

for detecting viruses for diagnosis (e.g. at first infection and during reactivation)
to monitor treatment of viral infection

Question 19

what is organism screening

Answer 19

sequence viral RNA/DNA to see how different it is to the consensus sequence (see if it has resistance genes) used to predict response to antivirals