PARASITOLOGY

• The most common procedure performed in the area of parasitology is stool specimen for ova and parasite.
• Ova is the egg stage of select parasites.

  Parasites encompasses morphologic forms.
• Microscopic Examination has three possible components:

  Collection, Transport, Fixatives
• Quality of the results is dependent on the appropriate specimen collection.
• Protozoan: Forms cysts and trophozoites
• Helminths: Eggs, Larvae, Proglottids, Adult Worm
• Three specimens: One specimen collected every other day.
• Three specimen within 10 days
• In amoebiasis, six specimen is required within 14 days.
• Medications and substances may interfere with the detection of parasites.
• Stool sample specimens from patient whose therapy includes:

  Bismuth, Barium, Mineral Oil should be collected prior therapy or 5-7 days after completion of therapy.
• Patients who have taken antibiotics and antimalarial should be delayed for 2 weeks following therapy.
• Stool specimen container should be:

  Clean

  Watertight

  Tight-fitting lid
• Amount required of stool: 2-5g
• Size of a walnut, thumb, pea
• Urine should not be allowed to contaminate stool as it is known to destroy parasites.
• Stool should not be retrieved from toilet bowl because of free-living protozoa and nematodes that may be confused with human parasites such as schistosomes, eggs, amebic trophozoites.
• Toilet paper in stool specimen is also not allowed as it may mask parasites or make examination difficult.
• Specimen should be labeled on the side of the container.
• Specimen is labelled with:

  Patients Name, ID number, Physician's Name, Date and Time of Collection.
• Specimen should be placed in a zip lock plastic bag for transport to laboratory.
• Suspected diagnosis, travel history, and clinical diagnosis may also be helpful but may not be provided.
• Time frame is also an important consideration in fecal examinations.

  Sample collection to receipt to specimen examination.
• Trophozoites are sensitive to environmental changes, feeding stage, motile, not stained by iodine, can be killed or disintegrated fast, liquid/watery stool.
• Cysts are nonmotile, nonfeeding, have cell wall, can survive for long period, stained by iodine, formed stool.
• Liquid/Water Specimen: Examined within 30 minutes.

  Semi-formed Specimen: Examined within 1 hour.

  Formed Specime: Held for 24 hours.
• Trophozoites: Liquid/Watery

  Trophozoites or Cysts: Semi-formed

  Cysts: Formed
• Specimen should be placed into preservative if guidelines are not followed. It can place the fixative directly at the time it was collected or at the receipt in the laboratory.
• Fixatives are substances that preserve morphology of protozoa and prevent further development of helminths eggs and larvae.
• Ratio of stool to fixative: 1:3
• Ratio of fixative to stool: 3:1
• Specimen must be fixed in the preservative for at least 30 minutes before processing begins.
• Choice of fixative depends on the preference of laboratory.
• Formalin is an all-purpose fixative to recover protozoa and helminths
• Formalin has 2 concentrations:

  5% preserves protozoa cysts

  10% preserves helminths eggs and larvae
• Formalin routinely used for direct examination and concentration techniques, NOT FOR PERMANENT SMEARS
• Formalin:

  Easy to use

  Preserve specimen for several years

  Long shelf life
• Formalin:

  Does not preserve morphology of parasites for permanent smears.

  Trophozoites are usually not recovered and details of cysts and helminths fade away in time.
• Formalin can be a potential health hazard.
• Polyvinyl Alcohol is a plastic powder that acts as an adhesive when preparing slides for staining.