Week 1: Intro Flashcards
Define parasitology
The study of a relationship among certain species
Give three examples of symbiosis
Mutualism
Commensalism
Parasitisim
Define facultative parasite
Free-living organisms that can become parasitic if accidentally ingested or enters a wound/other body opening
Define definitive host
A host in which the parasite reaches sexual or reproductive maturity
Define intermediate host
A host that harbors parasites that engage in asexual reproduction
Define transport host
A host that harbors a parasite that does not reproduce but merely goes on to infect a new host
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
List the 3 classifications of helminths using their two names (i.e. __worm and ___tode)
- Roundworms = nematodes
- Tapeworms = cestodes
- Flukes = trematodes
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
Identify the classification of helminth represented in the image
Roundworm (nematode)
Identify the classification of helminth represented in the image
Fluke (trematode)
Identify the classification of helminth represented in the image
Tapeworm (cestode)
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
Cysts are mostly abundant in which stool consistency?
Formed
Trophozoites are most abundant in which stool consistency?
Watery (so diarrhea)
Does 10% formalin guarantee that all parasitic forms are non-viable?
NO
Analyzing a fecal specimen by wet mount can use which preservative(s)?
- 10% formalin
- Formalin-ethyl acetate (FEA) for concentration
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)
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
- The sediment contains parasites
- Sediment is used to prep slides
- 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
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?
- Monochromic
- Stains parasites gray-black, nuclear material stains black, and background material stains light-blue gray
- 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
- Modified acid-fast (Cryptosporidium, Cyclospora, Isospora oocysts)
- Chromotrope staining (microsporidia spores)
- 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
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
- Rapid antigen test for malaria
- Immunodiagnosis (enzyme immunoassays and fluorescent Ab stains)
- Molecular diagnosis (e.g., PCR)
List 2 immunodiagnostic methods for detecting antibody or antigen of parasites
- Serology (helps detect if can’t see organism in testing or can’t obtain the specimen itself)
- Antigen testing (used mostly for stools with Giardia, Cryptosporidium, and E. histolytica)
