Parasitology and Stool Examination

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Questions and Answers

What can complicate the gross and microscopic examination of stool specimens?

Use of proper collection techniques

Presence of artifacts resembling parasites (correct)

Absence of human cells

Limited diet of vegetable and meat products

Free-living organisms found in stool do not lead to confusion in specimen analysis.

False

Name one type of cell that may mimic pathogenic protozoa in stool specimens.

PMNs (Polymorphonuclear leukocytes)

Improper collection techniques can lead to contamination of stool specimens with __________ organisms.

extraneous Signup and view all the answers

Match the following artifacts with their resemblance:

PMNs = Entamoeba histolytica/E.dispar cysts Macrophages = E.histolytica/E.dispar Signup and view all the answers

What are the recommended number of stool specimens for adequate parasite detection?

Three specimens collected over 10 days Signup and view all the answers

Urine contamination can help preserve parasites in stool samples.

False Signup and view all the answers

What is the acceptable stool sample amount required for a parasite study?

2 to 5 g Signup and view all the answers

Trophozoites and cysts are forms of ___ that can be recovered from stool samples.

protozoa Signup and view all the answers

Which of the following substances may interfere with the detection of parasites in stool specimens?

Antacids Signup and view all the answers

Match the following forms found in stool specimens with their classification:

Trophozoites = Protozoan form Cysts = Protozoan form Eggs = Helminth stage Larvae = Helminth stage Signup and view all the answers

What is the ideal condition for a stool specimen to be used for parasitic examination?

It should be processed immediately in the laboratory Signup and view all the answers

Toilet paper in the stool specimen can help in the examination of parasites.

False Signup and view all the answers

Up to six stool specimens can be collected to diagnose amebiasis within 14 days.

True Signup and view all the answers

How long should one wait to collect stool specimens after taking antiprotozoal or antihelminthic medications?

2 weeks Signup and view all the answers

What should be done if a fecal specimen cannot be processed immediately?

Place it in an appropriate preservative. Signup and view all the answers

The recommended fixative to stool ratio for successful recovery of parasites is __ parts fixative to one part stool.

three Signup and view all the answers

Match the following fixatives with their primary use:

Formalin = Recovery of helminthes eggs and protozoan cysts Modified PVA = Preservation of protozoa morphology SAF = Fixation and preservation of stool specimens MIF = Enhances visibility of protozoan cysts Signup and view all the answers

Which of the following should not be included in a stool sample collection instructions?

Include water from the toilet bowl Signup and view all the answers

Free-living protozoa and nematodes are typically mistaken for human parasites.

True Signup and view all the answers

What is one consequence of not using the correct preservative for stool specimens?

Loss of morphology of protozoa or development of helminthes. Signup and view all the answers

Study Notes

Examination of Stool Specimens

Gross and microscopic stool examination can be complicated by artifacts that resemble parasitic forms.
Artifacts may arise from daily consumption of various vegetable and meat products.
Human origin cells can mimic pathogenic protozoa, leading to misleading results.
Spurious infections can occur from ingesting contaminated or infected meats.
Improper collection techniques can lead to contamination with extraneous organisms.
Free-living organisms can confound results due to stool contact with water, sewage, or soil.

Artifacts Resembling Parasites

PMNs can resemble Entamoeba histolytica/E. dispar cysts.
Macrophages may be mistaken for E. histolytica/E. discreta.
Stool should not be retrieved from toilet bowl water due to potential contamination with free-living protozoa and nematodes.
Toilet paper can mask the presence of parasites in stool samples.

Collection Procedures

Use a clean, dry, leak-proof container without preservatives, and collect approximately 5 g of feces.
Close the container immediately after collection to avoid contamination.
Label the specimen with the patient's name, identification number, physician’s name, and date/time of collection.
Transfer the specimen to the laboratory promptly for analysis.

Preservation of Stool Specimens

Freshly collected stool samples are ideal for parasitic examination.
If immediate processing is not possible, specimens should be placed in appropriate preservatives.
Fixatives preserve protozoa morphology and prevent further development of certain helminth eggs and larvae.
Recommended fixative-to-stool ratio is three parts fixative to one part stool.

Common Fixatives

Formalin: All-purpose fixative for helminth eggs, larvae, and protozoan cysts.
Modified Polyvinyl Alcohol (PVA): Copper or zinc versions may be used.
Sodium Acetate Acetic Acid Formalin (SAF): Another option for specimen preservation.
Merthiolate Iodine Formalin (MIF): Used for enhancing specimen quality.
Schaudinn’s Fixative: Known for preserving detailed morphology.

Detection of Parasites

Morphological forms of protozoa and helminthes can be detected from well-collected and prepared stool specimens.
Protozoan stages (trophozoites and cysts) and helminth stages (eggs, larvae, segments, and adult worms) may be present.
Intermittent shedding of parasites necessitates collection of multiple specimens for accurate detection.
Protocol typically involves collecting three specimens every other day within 10 days; exceptions are noted for amebiasis diagnosis.

Precautions for Sample Collection

Always use gloves and a protective coat when handling specimens.
Certain medications (antacids, barium) can interfere with parasite detection; these effects may take days to clear.
Delay specimen collection for two weeks after antiprotozoal or antihelminth therapy.
Use a clean, watertight container with a tight-fitting lid.
Acceptable stool amount for parasite study is 2 to 5 g (size of a walnut).
Urine contamination must be avoided, as it can destroy some parasites.

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Description

This quiz focuses on the complexities of gross and microscopic stool examination, specifically the confusing presence of artifacts that may mimic parasitic organisms. It highlights how common dietary items can create misleading results and the potential for spurious infections related to food consumption.