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Medical Microbiology > Chapter 46 - Lab Dx of Parasitic Infections > Flashcards

Chapter 46 - Lab Dx of Parasitic Infections Flashcards

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1
Q

What are the 6 parasites of humans classified as?

A
  • Protozoa - amoeba
  • Nematoda (roundworms)
  • Platyhelminthes (flatworms)
  • Pentastomids (tongue worms)
  • Acanthocephala (thorny-headed worms)
  • Arthropoda - insects
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2
Q

Define zoonotic

A
  • infection that comes from animals
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3
Q

With parasitic infections, what does “status quo” refer to?

A
  • Both host and parasites are fine/healthy. The parasite doesn’t want to harm the host
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4
Q

When is “status quo” not followed?

A

Organisms tend to not cause disease unless their host is immunocompromised. Most people have potentially infectious organisms as part of their normal flora (S. aureus on skin, C. difficile in intestinal tract)

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5
Q

Define epidemiology

A
  • the study of the outbreak of diseases
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6
Q

What are 4 common modes of parasitic transmission and examples of each?

A
  • Venereal transmission (Trichomonas vaginalis)
  • Ingestion of contaminated food or water (Salmonella, E. coli)
  • Skin penetration of infective larvae (Strongyloides stercoralis, Hookworm)
  • Bites of various arthropods (Malaria, ZIKA)
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7
Q

Specimen Collection and Transport

  • When should preservatives be used?
  • When should they not be used?
A
  • should be used if a lag time exists
  • Free living organisms – don’t place in fixative
    Need to check for motility (Trichomonas vaginalis)
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8
Q

Specimen Collection and Transport

- what does processing depend on the use of?

A
  • Appropriate fixatives
    • Para-Pak EcoFix is a convenient one-vial system for the routine collection, transportation, preservation and examination of stool specimens for intestinal parasites.
  • Immediate fixation upon arrival
  • Adequate mixing of fixative and specimen
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9
Q

In what situations (2) are specimens considered STAT for processing?

A
  • Central nervous system (CNS) specimens for free-living amebae
  • Blood films for potential malaria
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10
Q

What are the following stains/fixatives used for?

  • Formalin
  • Trichrome stain
  • Modified iron hematoxylin stain
A
  • ether sedimentation fixes eggs, larvae, oocysts, and spores.
  • Distinguishes cysts and trophozoites.
  • Demonstrates cysts and trophozoites.
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11
Q

What are the following stains/fixatives used for?

  • Modified acid-fast stain
  • Modified trichrome stains
    • include examples (3)
A
  • Highlights Coccidia.
  • Differentiate microsporidia.
    • Weber-green
    • Ryan-blue
    • Kokoskin—hot method
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12
Q

What are the 6 common procedures for examining intestinal tract specimens?

A
  • Ova and parasites (O&P) examination
  • Recovery of tapeworm scolex
  • Examination for pinworm
  • Sigmoidoscopy
  • Duodenal drainage
  • Duodenal capsule technique
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13
Q

What are the 3 components of an ova & parasites examination?

A
  • Direct wet mount
  • Concentration
  • Permanent stain
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14
Q

Direct Smear

- Principle

A
  • To assess the worm burden of the patient, to allow quick diagnosis of heavily infected specimens, to check organism motility (primarily protozoan trophozoites), and to diagnose organisms that cannot be identified from the permanent stain methods; visible organism motility is the primary objective.
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15
Q

Direct Smear

  • Specimen
  • Reagents
A

Specimen
- Any fresh liquid or soft stool specimen that has not been refrigerated or frozen.
Reagents
- 0.85% NaCl; Lugol’s or D’Antoni’s iodine

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16
Q

Direct Smear

- Examination

A
  • Low-power examination (×100) of entire 22 × 22 mm coverslip preparation (both saline and iodine); high dry power examination (×400) of at least one third of the coverslip area (both saline and iodine).
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17
Q

Concentration
Examination

- Principle

A
  • To concentrate the parasites present, either through sedimentation or by flotation. The concentration is specifically designed to allow recovery of protozoan cysts, coccidian oocysts, microsporidian spores, and helminth eggs and larvae.
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18
Q

Concentration
Examination

  • Specimen
  • Reagents
A

Specimen
- Any stool specimen that is fresh or preserved.
Reagents
- 5% or 10% formalin, ethyl acetate, zinc sulfate (specific gravity, 1.18 for fresh stool and 1.20 for preserved stool); 0.85% sodium chloride (NaCl); Lugol’s or D’Antoni’s iodine.

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19
Q

Concentration

- Examination

A
  • Low-power examination (×100) of entire 22 × 22 mm coverslip preparation (iodine recommended but optional); high dry power examination (×400) of at least one third of the coverslip area (both saline and iodine).
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20
Q

Concentration
Examination

  • How should these results be marked?
  • What organisms can be identified definitively?
  • When can a final report be issued?
A
  • Often, results from the concentration examination should be considered presumptive
  • Exceptions: Giardia lamblia cysts and Entamoeba coli cysts, helminth eggs, and larvae, Isospora belli oocysts
  • after the results of the permanent stained smear become available
21
Q

Permanent Stained Smear

- Principle

A
  • To provide contrasting colors between the background debris and parasites present.
  • This technique is designed to allow examination and recognition of detailed organism morphology under oil immersion examination (×100 objective, for a total magnification of ×1000), primarily allowing recovery and identification of intestinal protozoa.
22
Q

Permanent Stained Smear

  • Results
    • how are the reports categorized?
    • why can they be categorized this way?
A
  • Most suspect protozoa and/or human cells can be confirmed by the permanent stained smear.
  • These reports should be categorized as “final” and are reported as such
23
Q

Permanent Stained Smear

  • what are the most common stains used?
  • what protozoa can’t be identified with these stains?
A

Stains:
- The most commonly used stains are trichrome and iron-hematoxylin.
Exceptions:
- helminth eggs and larvae (generally take up too much stain)
- Coccidian oocysts
- microsporidian spores

24
Q

Thin Blood Films

- Purpose

A
  • To provide contrasting colors for background debris and parasites present, either outside or within the red blood cells (RBCs).
  • This technique is designed to allow examination and recognition of detailed organism morphology under oil immersion examination, primarily allowing recovery and identification of Plasmodium spp., Babesia spp., Trypanosoma spp., Leishmania donovani, and filarial blood parasites
25
Q

Thin Blood Films

  • Con for parasitic ID compared to thick film?
  • What is the primary purpose?
  • What happens to the morphology of the RBCs in this method?
A
  • the number of organisms per field is significantly reduced compared with the thick blood film.
  • the primary purpose is to allow malarial parasites to be seen in the RBCs and to assess the size of infected RBCs compared with that of uninfected RBCs.
  • RBC morphology is preserved using this method
26
Q

Thin Blood Films

  • acceptable specimens?
  • reagents?
A

Specimens:
- Finger-stick blood, whole blood, or anticoagulated blood (EDTA recommended).
Reagents:
- Giemsa stain (films must be prefixed with absolute methanol before staining), Wright’s stain (the stain contains the fixative), or Wright-Giemsa stains and their associated solutions; mounting fluid (optional).

27
Q

Thin Blood Films

- Examination

A
  • Oil immersion examination (×1000) of AT LEAST 300 fields; additional fields may be required if suspect organisms have been seen in the thick blood film
28
Q

Thin Blood Films

- at what level of identification is this smear used for?

A
  • routinely used for parasite identification to the species level (Plasmodium spp.)
29
Q

Thin Blood Films

- what are the marks of a dirty or greasy slide?

A
  • Streaks in the film usually are caused by dirt; holes in the film indicate grease on the slide.
30
Q

Thin Blood Films

- What is the stain of choice for a thin blood film?

A
  • Giemsa stain
31
Q

Thin/Thick Blood Films

  • what is an example of a genus/species that Giemsa can’t stain?
  • what type of stain is necessary to stain that parasite?
A
  • Giemsa stain does not stain the sheath of Wuchereria bancrofti
  • hematoxylin-based stains (e.g., Delafield’s hematoxylin) are recommended for these organisms
32
Q

Thin/Thick Blood Films

- What cells are used as the QC for acceptability of the film?

A
  • The WBCs on the stained blood film serve as the quality control; if the WBC morphology and color are acceptable, then any parasites present will also appear normal and will be acceptable.
33
Q

Thick Blood Films

- What is this technique primarily used for and why?

A
  • The thick blood film is routinely used for detection of parasites, because the number of organisms per field is much greater than with the thin blood film.
  • The primary purpose is to allow examination of a larger volume of blood than is seen with the thin blood film
34
Q

Thick Blood Films

  • Specimen type?
  • Reagents?
A
  • Finger-stick blood, whole blood, or anticoagulated (EDTA) blood
  • Giemsa, Wright’s, or Wright-Giemsa stain and associated solutions
35
Q

Thick Blood Films

  • Is RBC morphology preserved?
  • What is done to achieve this?
A
  • Red blood cell (RBC) morphology is not preserved using this method.
  • The blood films must be laked before or during staining (rupture of all RBCs); the only structures that are left on the blood film are white blood cells, platelets, and parasites
36
Q

Thick Blood Films

  • How many fields must be examined?
  • What type of microscopic examination is necessary?
A
  • Oil immersion examination (×1000) of at least 300 fields; additional fields may be required if suspect organisms have been seen in the thin blood film.
37
Q

Thick Blood Films

- What are these used to detect?

A
  • routinely used to detect the presence of parasites
38
Q

Thick Blood Films

  • Amount of blood
  • Smear prep process
  • What etra step is taken in this prep that the thin prep doesn’t require?
A
  • The thick blood film is prepared by spreading a few drops of blood (using a circular motion) over an area approximately 2 cm in diameter.
  • If whole blood is used, the examiner should continue stirring about 30 seconds to prevent the formation of fibrin strands
  • After they are thoroughly dry, they can be laked to remove the hemoglobin
39
Q

What are the 4 steps involved in a pinworm collection & examination?

A
  1. Obtain a piece of clear sticky tape about 4 inches long
  2. Hold the tape between the thumbs and forefingers
  3. Before the child has woken in the morning, press the sticky side against the skin across the anal opening
    - Gently place the sticky side of the tape against the surface of a clear glass slide. Label the slide.
40
Q
  • What type of specimen is Trichomonas vaginalis usually seen in?
  • How are they typically observed?
  • What other tests can detect it?
A
  • typically observed in urogenital specimens.
  • Motile organisms are observed under low power (100x).
  • Direct antigen tests
41
Q

What are some organisms (7) that can be found in sputum?

A
  • Ascaris lumbricoides larvae
  • Strongyloides stercoralis
  • Hookworm
  • Paragonimus spp. eggs
  • Echinococcus granulosus hooklets
  • Protozoa
  • Microsporidia
42
Q

What are some examples (6) of aspirates that may be collected for examination?

A
  • Fine-needle aspirates
  • Duodenal aspirates
  • Bronchoalveolar lavages
  • Bronchial washings
  • Bone marrow
  • Spinal fluid
43
Q

What are three different types of procedures used to examine tissue?

A
  • Impression smears
  • Tease mounts
  • Squash preparations
44
Q
  • What is a buffy coat preparation?

- What parasites is it used to find?

A
  • A smear of the white blood cell (WBC) layer of peripheral blood is scanned.
  • Organisms such as L. donovani, trypanosomes, and Histoplasma capsulatum (fungus) are found in WBCs.
45
Q
  • What are some examples (4) of direct detection tests for intestinal parasites?
  • What are some examples (4) of the parasites found on these types of tests?
A
  • Antigen detection using direct fluorescent antibody (DFA)
  • enzyme immunoassay (EIA)
  • immunofluorescent antibody (IFA)
  • cartridges (immunochromogenic)
  • Entamoeba histolytica
  • Entamoeba histolytica–Entamoeba dispar group
  • Giardia lamblia
  • Cryptosporidium spp.
46
Q
  • What does species does cultivation help distinguish between?
  • Ho do they do it?
A
  • S. stercoralis, hookworm, and Trichostrongylus

- Allow the development of larvae into filariform stages.

47
Q

What are some of the protozoan parasites (7) that labs culture for?

A
  • Entamoeba histolytica
  • Naegleria fowleri
  • Acanthamoeba spp.
  • Trichomonas vaginalis
  • Toxoplasma gondii
  • Trypanosoma cruzi
  • Leishmaniasis
48
Q

What are the three main preventive measures to prevent the spread of parasites?

A
  • Personal hygiene
  • Proper sanitation
  • Elimination of sexual activities that potentiate fecal-oral contact

Medical Microbiology (6 decks)

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