Week 1: Intro Flashcards by MC GC

Define parasitology

The study of a relationship among certain species

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Give three examples of symbiosis

Mutualism
Commensalism
Parasitisim

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Define facultative parasite

Free-living organisms that can become parasitic if accidentally ingested or enters a wound/other body opening

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Define definitive host

A host in which the parasite reaches sexual or reproductive maturity

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Define intermediate host

A host that harbors parasites that engage in asexual reproduction

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Define transport host

A host that harbors a parasite that does not reproduce but merely goes on to infect a new host

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List the 4 classes of protozoa and briefly describe how they move

Amoeba: pseudopodia
Flagellates: flagella
Ciliates: cilia
Sporozoa: nonmotile blood/tissue parasites with alternating sexual and asexual generations

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List the 3 classifications of helminths using their two names (i.e. __worm and ___tode)

Roundworms = nematodes
Tapeworms = cestodes
Flukes = trematodes

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Describe the body structures of roundworms (nematodes), tapeworms (cestodes), and flukes (trematodes)

Roundworms = cross-sectional body is round

Tapeworms = flattened/segmented body

Flukes = flattened, leaf-shaped, non-segmented body

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Identify the classification of helminth represented in the image

Roundworm (nematode)

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Identify the classification of helminth represented in the image

Fluke (trematode)

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Identify the classification of helminth represented in the image

Tapeworm (cestode)

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For fecal samples, describe 1) the fresh sample time criteria and 2) specimen preservatives used (include stool to preservative ratios)

1) Examine, process, and preserve IMMEDIATELY
2) Store in two separate containers, each with different preservative. One container will have 10% formalin and the other will have PVA (polyvinyl-alcohol) preservative. Add 1 volume of stool to 3 volumes of preservative

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Cysts are mostly abundant in which stool consistency?

Formed

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Trophozoites are most abundant in which stool consistency?

Watery (so diarrhea)

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Does 10% formalin guarantee that all parasitic forms are non-viable?

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Analyzing a fecal specimen by wet mount can use which preservative(s)?

10% formalin
Formalin-ethyl acetate (FEA) for concentration

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FEA concentration method can be used for which fecal specimen procedures? Indicate organism analyzed by each procedure

Wet mount (helminths + protozoa)
Direct mount (Cyclospora + Isospora)
Acid fast stain (Cryptosporidium, Cyclospora, + Isospora)
Direct immunofluorescence assay (Giardia and Cryptosporidium)
Safranin stain (Cyclospora)

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Fecal specimens in PVA preservative can be used with which procedure(s)? Indicate organism analyzed by procedure(s)

Trichrome stain (protozoa)

Specimens preserved in 10% formalin can be used for wet mount, ELISA, and chromotrope stain procedures. Indicate the correct organisms each procedure analyzes

Wet mount = helminths + protozoa
ELISA = Giardia + Cryptosporidium
Chromotrope stain = microsporidia

Describe 3 big-picture methods involved in microscopic examination of fecal samples

Direct wet mounts to look for motile protozoan trophy
Concentrates
Permanent stained smears

What is the time frame for direct wet mounts of watery or formed stool?

Within 30 min after initial collection

Direct wet mount samples use saline or iodine. Why do you use these reagents?

Saline: motility of trophozoites -> look more refractile

Iodine: destroy trophozoite motility, and stains glycogen
Highlights internal structures of parasites

Briefly describe the sedimentation method for concentrating fecal samples. Definitely include which reagent it uses and where parasites concentrate!

Uses formalin-ethyl acetate (FEA), which has a lower specific gravity than organisms such that the organisms concentrate in the sediment under the solution.

Briefly describe the flotation method for concentrating fecal samples. Definitely include which reagent it uses and where parasites concentrate!

Uses Zinc Sulfate solution, which has a higher specific gravity than parasites, so the organisms concentrate in the flotation. You may miss some dense organisms if settling occurs. Eliminates some fecal debris

This image shows FEA concentration after centrifugation. Label the different density layers and indicate 1) which layer contains parasites, 2) what sediment is used for, and 3) whether trophs survive or not

1. The sediment contains parasites 2. Sediment is used to prep slides 3. Protozoan trophs do NOT usually survive

Explain the different uses for saline and iodine wet mounts (i.e., which parasite types are they used to ID?)

Saline: for visualizing trophozoites, protozoan cysts, and helminth ova/larvae Iodine: To identify protozoan cysts

Explain how you microscopically examine/analyze fecal wet mount samples on the microscope (hint: which objectives, which scanning pattern)

Scan field with 10x first using a zig-zag pattern. Then switch to 40x to help identify objects. Only use 100x oil if slide is SEALED.

What is the "gold standard" method of identifying protozoan cysts and trophs?

Stained smears!

Here are two wet mounts. Identify which one uses saline and which one uses iodine

See image

If fecal sample is unpreserved, then which fixative do you use?

Schaudinn

List advantages and disadvantages of 10% formalin fixative

Advantages: Good preservation of morphology (cysts, eggs, larvae, coccidia), concentration procedures, acid-fast stains, easy to prep, all purpose fixative, long shelf-life Disadvantages: Not good for trichrome stain! Bad morphological preservation of trophozoites CDC link: [https://www.cdc.gov/dpdx/diagnosticprocedures/stool/specimencoll.html](http://)

List advantages and disadvantages of PVA (low-viscosity in CDC website)

Advantages: Good morphological preservation of BOTH trophs and cysts, can be used for permanent stains such as trichrome, preserves samples for a long time Disadvantages: Bad morphological preservation of helminth eggs/larvae, and coccidia, Has mercuric chloride (difficult to dispose of), bad for concentration procedures CDC link: https://www.cdc.gov/dpdx/diagnosticprocedures/stool/specimencoll.html

Modified PVA with which two metals can be used? Advantages and disadvantages?

Zinc and copper. Can be used for trichrome staining BUT inconsistent staining and bad morphological preservation compared to LV-PVA preserved samples

Describe following for the IRON HEMATOXYLIN STAIN: 1. Monochromic or polychromic 2. Colors that you see on slide 3. How easy is the procedure?

1. Monochromic 2. Stains parasites gray-black, nuclear material stains black, and background material stains light-blue gray 3. Difficult procedure with variability in results. It's hard to find things

Describe the colors you see in different structures, using a trichrome stain

-Cyst and troph cytoplasms stain blue-green tinged with purple -Nuclear chromatin and ingested RBCs stain red or red-purple -Green background

List 3 other stains used for fecal specimens and the organisms they're used to identify

1. Modified acid-fast (Cryptosporidium, Cyclospora, Isospora oocysts) 2. Chromotrope staining (microsporidia spores) 3. Calcofluor White staining (microsporidia, Acanthamoeba, Pneumocystis)

If an organism is positive for an acid fast stain, which color does it stain? What about negative?

Positive = fuchsia Negative = blue

What is the time frame for making a blood smear?

Within 2 hours of collection

Distinguish the uses between Giemsa and Wright-Giemsa stains (yes, they are different)

Giemsa: Recommended for detection and identification of blood parasites. Wright-Giemsa: Used in hematology. Not optimal for blood parasites. Can use if rapid results are needed but follow up with Giemsa stain CDC link: [https://www.cdc.gov/dpdx/diagnosticprocedures/blood/staining.html](http://)

Distinguish between the uses of thick and thin blood smears

Thick smears: to find parasites, especially rare forms Thin smears: To identify parasites

How do you prepare thick smears?

Allow drop of blood to dry for about 6 hours before staining (RBCs will be lysed)

How do you prepare thin smears?

Fix in methanol prior to staining. Methanol prevents RBC lysis

List 3 non-microscopic methods for parasitology testing

1. Rapid antigen test for malaria 2. Immunodiagnosis (enzyme immunoassays and fluorescent Ab stains) 3. Molecular diagnosis (e.g., PCR)

List 2 immunodiagnostic methods for detecting antibody or antigen of parasites

1. Serology (helps detect if can't see organism in testing or can't obtain the specimen itself) 2. Antigen testing (used mostly for stools with Giardia, Cryptosporidium, and E. histolytica)