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Virology > Diagnosis of Viral Infections > Flashcards

Diagnosis of Viral Infections Flashcards

1
Q

risk group 1

A

no or low individual and community risk

ex. adeno-associated virus

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2
Q

risk group 2

A

moderate individual risk, low community risk; risk of spread of infection limited
ex. herpes viruses, foot-and-mouth disease

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3
Q

risk group 3

A

high individual risk, low community risk; doesn’t ordinarily spread from one infected individual to another; effective tx available
ex. HIV, hepatitis B, hantaviruses

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4
Q

risk group 4

A

high individual and community risk; effective tx and preventative measure not usually available
ex. Lassa fever, smallpox, influenza

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5
Q

What requirements exist for BSL-4 labs?

A
  • positively air pressured suit
  • negative air pressure in lab room
  • HEPA filtered air
  • double autoclave
  • suit decontamination shower
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6
Q

What risk group is handled at BSL4 labs?

A

risk group 4 (E.g. Ebola)

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7
Q

biohazard

A

biological substances that pose a threat to the health of living organisms

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8
Q

biosafety

A

containment principles, technologies and practices that are implemented to prevent the unintentional exposure to pathogens and toxins, or their accidental release

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9
Q

aerosol

A

very small droplets of fluid that can spread via air

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10
Q

biosafety cabinets (BSC)

A

enclosed, ventilated laboratory workspace for safely working with materials contaminated with pathogens requiring a defined biosafety level

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11
Q

biosecurity

A

protection, control and accountability for valuable biological materials within labs, in order to prevent their unauthorized access, loss, theft, misuse, diversion or intentional release

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12
Q

successful detection of viruses from a sample depends on:

A
  • collection of sample from right site
  • at right time
  • from most appropriate animal
  • proper transport and storage of sample
  • performing correct diagnostic test
  • proper interpretation of results
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13
Q

When is the chance of viral recovery best?

A

during first 3 days after onset; greatly reduced beyond 5 days

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14
Q

When should blood samples be collected for serological tests?

A

one during acute phase of illness and one during convalescence period (10-14 days after 1st)

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15
Q

When should specimens for PCR be collected?

A

during early part of the illness

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16
Q

Where should samples be collected for respiratory and ocular disease?

A

live: nasal and conjunctival swabs, blood
postmortem: tissues from affected system, lymph nodes

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17
Q

Where should samples be collected for skin disease and lesions of mucous membranes?

A

live: scrapings of lesion, swab affected area, blood
postmortem: tisues from affected system, LN

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18
Q

Where should samples be collected for gastroenteritis?

A

live: feces, blood
postmortem: tissues from affected system, LN, intestinal contents

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19
Q

Where should samples be collected for systemic disease ?

A

live: blood, nasal and urogenital swabs, feces
postmortem: tissues from various organs

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20
Q

Where should samples be collected for CNS disease?

A

live: blood, CSF, feces, nasal and urogenital swabs
postmortem: tissues from affected system, LN

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21
Q

Where should samples be collected for disease of urinary tract ?

A

live: urogenital swab, urine, blood
postmortem: tissues from affected system, LN

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22
Q

Where should samples be collected for abortion?

A

live: blood from dam, vaginal mucus
postmortem: tissues from placenta and fetus; blood from fetal heart; intestinal contents

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23
Q

How much blood should be sampled for serological testing?

A

10-20 mL for large animals and 5-10 mL for small animals

*clotted sample for serology and sample with anticoagulant for other tests

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24
Q

Should you freeze samples?

A

NO refrigerate at 2-8 C; if they have to be frozen, freeze rapidly at -20 C or - 70C

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25
Q

T/F specimens for histo examination should never be frozen

A

T

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26
Q

How should histo samples be fixed?

A

10% buffered fomalin or fixatives

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27
Q

viral transport medium (VTM)

A

prevents specimen from drying, helps maintain viral viability and retards growth of microbial contaminants; consists of buffered salt solution with added protein and antimicrobials

28
Q

3 potential hazards associated with transportation of pathogens

A
  1. breakage of containers
  2. exposure to possible infection
  3. delays in package delivery to diagnostic lab
29
Q

Whats the best way to prevent spillage?

A

basic triple packaging system

30
Q

processing samples

A
  • tissue homogenization (Ten Broeck grinder, mortar and pestle)
  • vortex mixer and centrifuge for feces and swabs
31
Q

negative stain electron microscopy

A

virus sample mixed with solution of heavy metal salt that is highly opaque to electrons (sodium phosphotungstate or uranyl acetate) then spread on thin layer on carbon-coated copper grid and dried

32
Q

How many virions must fluid matrix contain for virus particles to be detected by negative stain electron microscopy?

A

10^6 - 10^7 virions /mL

33
Q

TEM

A

based on transmitted electrons; 2D images with higher mag and greater resolution than SEM

34
Q

SEM

A

based on scattered electrons; 3D image of the surface

35
Q

assay

A

qualitative or quantitative measurement of a target entity/analyte

36
Q

gold standard test

A

diagnostic test that is considered to be the most accurate and best available under a particular condition or set of conditions

37
Q

negative predictive value (NPV)

A

probability that a negative test result accurately indicates the absence of infection

38
Q

positive predictive value (PPV)

A

probability of a positive result accurately indicating presence of infection

39
Q

sensitivity

A

probability that cases with the infection will have a positive result using the test under evaluation

40
Q

specificity

A

probability that cases without the infection will have a negative result using the test under evaluation

41
Q

serum

A

clear yellowish fluid obtained upon separating whole blood into its solid and liquid components after it has been allowed to clot
*put in red top vacutainer tube

42
Q

plasma

A

produced when whole blood is collected in tubes that are treated with an anticoagulant; cells removed by centrifugation
*put in lavender-top EDTA vacutainer tube

43
Q

Whats the make up of blood ?

A
  • plasma 55% total blood

- buffy coat (leukocytes and platelets)

44
Q

What indicates a positive reaction in an ELISA?

A

intensity of color

45
Q

direct ELISA

A

antigens are immobilized and enzyme-conjugated primary antibodies are used to detect or quantify antigen concentration; specificity of primary antibody is very important

46
Q

indirect ELISA

A

primary antibodies are not labeled, but detected instead with enzyme-conjugated secondary antibodies that recognize the primary antibodies

47
Q

sandwich ELISA

A

antigen to be measured is bound between a layer of capture antibodies and a layer of detection antibodies; two antibodies must be critically chosen to prevent cross-reactivity or competition of binding sites

48
Q

competitive ELISA

A

antigen of interest from the sample and purified immobilized antigen compete for binding to the capture antibody; decrease in signal when compared to assay wells with purified antigen alone indicates the presence of antigens in the sample

49
Q

fluorescence antibody test (FAT)

A

antibodies labelled with a fluorescent dye (FITC or rhodamine) so that visible fluorescence appears following Ag-Ab reaction

can be direct or indirect (IFAT)

50
Q

immunohistochemistry

A

antibody tagged with enzyme, generally horseradish preoxidase; enzyme reacts with substrate to produce a colored product that can be visualized in the infected cells with a standard light microscope
*direct or indirect

51
Q

immunochromatography

A

aka lateral flow devices
point of care test that is simple to perform, easy to carry, and doesn’t require specialized equipment

*HIV test, pregnancy test

2 lines = positive, 1 line = control

52
Q

point of care (POC)

A

diagnostic testing performed at or near the patient’s site of care

53
Q

With immunochromatography, what are the antibodies labeled with?

A

colloidal gold

54
Q

agglutination

A

method using property of specific antibodies to bind many antigens into single clumps thereby forming large complexes which are easily precipitated (visible macroscopically or microscopically)

55
Q

hemagglutination

A

relies on property of some pathogens (mainly viruses) to nonspecifically agglutinate erythrocytes

56
Q

What has the hemagglutination inhibition test been used for?

A

detection of serotype specific antibodies against avian influenze and peste des petits ruminants (PPR)

57
Q

hemagglutination inhibition test

A

virus will bind to antibodies instead of RBC so no agglutination

58
Q

agar gel immunodiffusion test

A

antigen and antibody placed in separate wells of an agar gel -> diffuse toward each other -> thin white line formed due to precipitation of ag-ab complex

59
Q

When is agar gel immunodiffusion test used?

A

to detect antibodies against avian influenza (matrix antibodies), EIA (coggins) and enzootic bovine leukosis

60
Q

complement fixation test

A

reactive: RBC settle in pellet -> no lysis
nonreactive: RBCs lysed by unbound complement

61
Q

immunoblotting

A

antigen samples separated via gel (smaller go farther) and blotted onto nitrocellulose sheet -> specific antigen bind to corresponding labelled antibody -> autoradiography -> antigen bands visualized

62
Q

hemadsorption

A

glycoproteins inserted into host cell membrane at sites of budding of enveloped viruses -> allows monolayer cells to adsorb RBC on their cell membranes

63
Q

hemadsorption-inhibition assay

A

infected monolayer cells incubated with known specific antibody -> antibodies bind to viral glycoproteins in cell membrane -> wash away antibodies that aren’t bound to viral proteins -> pretreated monolayer cells are incubated with RBCs -> RBC binding inhibited

64
Q

neutralization assay

A

antibody bound virus (neutralized) becomes non-infectious and can’t produce desired effects in eggs, cell-lines or animals

65
Q

How can unneutralized virus be detected?

A

CPE, hemadsorption, hemagglutination, plaque formation, disease in animals

66
Q

What is indicative of recent infection?

A

IgM antibodies -> appear early after infection but drop to low levels within 1-2 months and disappear within 3 months

Virology (16 decks)

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