Medical Parasitology Lab Techniques

Stool Examination

• Stool color is important in indicating the condition: brown is normal due to bilirubin, a byproduct of heme in hemoglobin.

Modified Polyvinyl Alcohol (MPVA)

• Alternative to mercury-based PVA
• Contains copper sulfate or zinc sulfate
• Used in concentration methods and permanent stained smears
• Disadvantages:
  • Does not provide the same quality of preservation for adequate protozoan morphology on a permanent stained slide as mercury-based fixatives
  • Parasite identification is difficult
  • More likely negatively affected if proper protocol is not followed

Schaudinn's Fixative (SF)

• Preserves morphologic protozoan, trophozoite, and cysts
• Easy to prepare for permanent staining
• Disadvantages:
  • Less suitable for concentration technique
  • Contains mercury chloride
  • Inadequate preservation of helminth eggs, larvae, coccidian, and microsporidia

Stool Preparation and Examination

• Direct iodine wet preparation: enhances detail of protozoan cysts
• Direct saline wet preparation: enhances detail of protozoa
• Concentration method: uses 2.5g of stool, purpose is to aggregate parasites and remove small debris
• Novy-MacNeal-Nicolle (NNN) medium: used for the recovery of Leshamania spp.

Reporting of Results

• Should state scientific name (genus and species)
• Ex: Entamoeba histolytica cyst seen

Additional Infos

• Is bacteria need to be reported? No, but it depends on the protocol
• In general, most parasites are not quantified; amoeba-presence or absence is reported

Specimen Processing and Laboratory Testing

• Proper specimen selection and processing are crucial to parasite recovery
• When zinc sulfate is added to the specimen and centrifuged, the parasites float to the surface and can be skimmed from the top of the tube
• Advantage: more fecal debris is removed, making it easier for microscopic examination
• Disadvantage: some helminth eggs are very dense and will not float, thus, some parasites will be missed

Materials Needed

• Gauze
• Conical centrifuge tube (15mL)
• Normal saline solution (0.85% / 10% formalin)
• Centrifuge
• Zinc sulfate solution
• Disposable Pasteur pipette/bent wire loop/
• Slides and coverslip
• Iodine solution
• Stool sample

Procedure

• Strain the specimen through a filter containing a single-layer thickness of gauze into a conical tube
• Fill the tube with saline or 10% formalin and centrifuge for 10 minutes at 500 x G (1500rpm)
• Decant the supernatant and repeat if necessary

Permanent Stain

• The use of stained slide preparation provides a permanent record of a patient's specimen and allows review by a consultant
• Permanent stain is designed for analysis using the oil immersion objective (100x)
• 300 fields must be reviewed before the slide can be considered negative
• Designed to detect protozoan cyst and trophozoites
• Staining allows to observe detailed features of protozoa by making its intracellular organelles visible

This quiz covers the laboratory techniques used in medical parasitology, including the use of Modified Polyvinyl Alcohol (MPVA) and the importance of stool color in diagnosis. It also touches on concentration methods and permanent stained smears.