Clinical Parasitology Lab Prelims

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Questions and Answers

What is the primary purpose of concentration method in parasitology?

To aggregate parasites into a small volume of sample and remove debris (correct)

To observe detailed features of protozoa without staining

To detect large numbers of parasites

To identify helminth eggs and larvae

What type of sample is recommended for staining in concentration method?

Formalin-fixed sample

Thickly prepared slide of PVA preserved sample

Fresh stool specimen without fixative

Thinly prepared slide of PVA preserved sample (correct)

What is the limitation of using concentration method for helminth eggs and larvae?

They are not typically found in fecal samples

They are easily destroyed by centrifugation

They are difficult to detect

They stain too dark or appear distorted (correct)

What is the process of fixing a sample with SAF limited to?

Iron-hematoxylin staining Signup and view all the answers

What is the benefit of using a fixative such as Schaundinn's fixative on fresh stool specimen?

It prevents the degradation of parasites Signup and view all the answers

What is the purpose of sealing the slides with a permanent mounting sealant after staining?

To preserve the slides for future examination Signup and view all the answers

What type of parasites can be detected using concentration method?

Protozoan cysts, oocysts, helminth eggs, and larvae Signup and view all the answers

What is the principle behind concentration techniques in parasitology?

Differences in specific gravity and centrifugation Signup and view all the answers

What is the primary advantage of using mercury-containing preservatives when preparing protozoa specimens?

They preserve parasite morphology adequately for permanent smears. Signup and view all the answers

What is the limitation of using trophozoites with PVA fixation?

They cannot be recovered and morphologic details may fade with time. Signup and view all the answers

What is the primary difference between zinc sulfate and copper sulfate fixatives?

Zinc sulfate is more effective for preserving morphology, while copper sulfate is better for concentration. Signup and view all the answers

What is the primary advantage of using Schaundinn's Fixative?

It provides better preservation of protozoa morphology than PVA fixation. Signup and view all the answers

What is the primary reason for the prevalence of parasitic diseases in underdeveloped tropical and subtropical countries?

Poor sanitation and personal hygiene practices of the inhabitants Signup and view all the answers

When should a sample be collected from a patient who is taking antibiotic or anti-malarial drug?

2 weeks after starting the therapy Signup and view all the answers

What is the limitation of using PVA fixation for protozoa preparation?

It does not preserve morphology of protozoa trophozoites and cysts well. Signup and view all the answers

What is the minimum acceptable amount of stool for parasitic analysis?

2.5 grams Signup and view all the answers

What is the primary difference between PVA and modified PVA fixation?

PVA contains mercuric chloride, while modified PVA does not. Signup and view all the answers

What is the primary advantage of using modified PVA fixation?

It is an alternative to mercury-based PVA fixation. Signup and view all the answers

Why should stool samples not be contaminated with urine?

Urine may destroy the parasites in the stool Signup and view all the answers

What is the primary reason for collecting stool samples in a clean, water-tight container with a tight-fitting lid?

To prevent contamination with free-living protozoa and nematodes Signup and view all the answers

What is the primary disadvantage of using mercury-containing fixatives?

They have toxic properties. Signup and view all the answers

What is the significance of the 3 phases in laboratory analysis of parasitic diseases?

To ensure accurate and reliable laboratory results Signup and view all the answers

Why should samples from patients who are taking barium or bismuth be collected 5-7 days before or after taking the drug?

To prevent interference with laboratory test results Signup and view all the answers

What is a common challenge in laboratory identification of parasites?

Distinguishing between human and free-living parasites Signup and view all the answers

What is the principle of the Formalin-Ethyl Acetate Sedimentation Procedure?

Parasites are heavier than the solution and settle in the sediment Signup and view all the answers

What is the ideal number of fields to be reviewed under OIO (100x) for a slide to be considered negative?

300 fields Signup and view all the answers

Which of the following parasites may not be recovered from duodenal material?

Taenia saginata Signup and view all the answers

What is the advantage of collecting duodenal material using nasogastric intubation or enteric capsule test?

It increases the chances of recovering parasites that reside in the small intestine Signup and view all the answers

What is the primary difference between sedimentation and flotation techniques?

In sedimentation, parasites settle in the sediment, while in flotation, they float to the surface Signup and view all the answers

What is the recommended procedure for examining duodenal material if the volume is greater than 2mL?

Centrifugation and examination of the sediment Signup and view all the answers

What is the primary advantage of using Trichrome stain?

It has a long shelf life and is easy to use Signup and view all the answers

Which of the following stains is commonly used to examine duodenal material?

Iron hematoxylin Signup and view all the answers

What is the primary use of Acid fast stain?

Detection of Cryptosporidium, Isospora, and Cyclospora Signup and view all the answers

What is the purpose of stool screening methods?

To detect antigen in a patient's specimen Signup and view all the answers

Which of the following parasites is not typically recovered from duodenal material?

Toxoplasma gondii Signup and view all the answers

What is the purpose of fixing duodenal material with PVA?

To preserve the material for later examination Signup and view all the answers

What is the primary advantage of using Modified iron hematoxylin stain?

It detects acid-fast parasites in addition to other protozoa Signup and view all the answers

What is the purpose of reviewing multiple fields under OIO (100x) for a slide to be considered negative?

To ensure the absence of parasites in the sample Signup and view all the answers

What is the benefit of collecting duodenal material over traditional stool specimens?

It allows for the recovery of parasites that may not be present in stool Signup and view all the answers

Which of the following is not a common method for collecting duodenal material?

Sigmoidoscopy Signup and view all the answers

Study Notes

Laboratory Analysis of Parasites

Parasitic disease is a significant global threat, prevalent in underdeveloped tropical and subtropical countries due to climatic conditions and poor sanitation.
Clinicians need to understand laboratory tests to identify parasites accurately.

Specimen Collection and Handling

Samples from patients taking interfering medications (barium, bismuth, mineral oil, antibiotics, or anti-malarial drugs) must be collected 5-7 days before or after therapy.
Stool specimens must be collected in a clean, water-tight container with a tight-fitting lid.
Acceptable stool amount is 2.5 grams (walnut or pea size).
Stool must not be contaminated with urine, which can destroy parasites.
Stool must not be retrieved from the toilet bowl to avoid free-living protozoa and nematodes.

Phases of Laboratory Analysis

The three phases are:
1. Concentration Method
2. Staining and Microscopy
3. Identification and Reporting

Concentration Methods

Purpose is to aggregate parasites in a small sample volume and remove debris.
Techniques can be performed on fresh or preserved specimens.
Enables detection of: • Protozoan cysts • Oocysts • Helminth eggs • Larvae

Fixatives for Permanent Smears

PVA (polyvinyl alcohol) is commonly used with Schaundinn solution as a base.
Advantages: easy to prepare, long shelf life, and preserves protozoan trophozoites, cysts, and helminth eggs.
Disadvantages: does not preserve morphology adequately, and trophozoites can't be recovered.

Stains for Routine O&P Testing

Trichrome stain (Wheatley Trichrome) • Most widely used permanent stain • Easy procedure and long shelf life
Iron hematoxylin • Reveals excellent morphology of intestinal protozoa • Considered time-consuming

Specialized Stains

Acid fast stain • Detection of Cryptosporidium, Isospora, and Cyclospora oocysts
Modified iron hematoxylin • Detection of acid-fast parasites and other protozoa

Duodenal Material Examination

Collection methods: nasogastric intubation or enteric capsule test (entero test)
Recovery of parasites: • Giardia intestinalis trophozoites • Cryptosporidum spp • Isospera belli • Strongyloides stercoralis • Ova of Fasciola hepatica or Clonorchis sinensis

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Description

This quiz covers the basics of clinical parasitology, including specimen collection and handling, and the effects of certain substances on lab results.