40 Questions
What is the primary disadvantage of using permanent stains in preserving protozoa morphology?
It does not preserve parasite morphology adequately
What is the alternative to mercury-based PVA in modified PVA?
Both a and b
What is the advantage of using Schaundinn's fixative?
It is easy to prepare and preserves morphology of protozoan trophozoite and cysts
What is the primary advantage of using mercury-containing preservatives?
They preserve parasite morphology adequately
Which of the following is a limitation of direct wet preparation for the examination of O&P?
It cannot be performed on a specimen received in a fixative.
What is the limitation of using trophozoites in permanent stained smears?
They can't be recovered and morphologic details of cysts and egg may fade with time
What is the primary disadvantage of using PVA in preparing slides for staining?
It does not preserve parasite morphology adequately
Which of the following stool colors is associated with upper GI bleeding?
Black
What is the purpose of adding iodine to a stool specimen in direct wet preparation?
To enhance the detection of protozoan cysts
What is the advantage of using modified PVA in concentration methods?
It is suitable for concentration methods
Which of the following is NOT a type of direct wet preparation?
Concentration technique
What is the primary disadvantage of using Schaundinn's fixative?
It is less suitable for concentration
What is a possible cause of a pale yellow-colored stool?
Bile duct obstruction
Which of the following organisms can be detected using direct wet preparation?
Helminth eggs
What is a characteristic of direct wet preparation using saline?
It can demonstrate motility
Which of the following is NOT a possible cause of a red-colored stool?
Bile duct obstruction
What is the primary advantage of using the Direct Saline Wet Preparation technique?
It yields good recovery of most parasites and is easy to perform
What is the purpose of using a 22-mm square coverslip in the Direct Saline Wet Preparation?
To ensure the mixture is thin enough for newspaper print to be read through
What is the primary reason why parasitic diseases are prevalent in underdeveloped tropical and subtropical countries?
Poor sanitation and personal hygiene practices
What is the main difference between the Direct Saline Wet Preparation and the Zinc Sulfate Flotation Technique?
The way the parasites are recovered
What is the effect of iodine on trophozoites in the Direct Iodine Preparation?
It kills them
What is the recommended duration before or after taking a drug that interferes with sample collection?
5-7 days
What is the primary advantage of using the Zinc Sulfate Flotation Technique?
It provides a cleaner preparation with less fecal debris
What is the minimum acceptable amount of stool required for analysis?
2.5 grams
Why is it important to avoid collecting stool samples from the toilet bowl?
Risk of contamination with free-living protozoa and nematodes
What is the main disadvantage of using the Direct Saline Wet Preparation technique?
It contains more fecal debris and is more challenging to the microscopist
What is the purpose of using Lugol's Iodine or D'Antoni's formula in the Direct Iodine Preparation?
To enhance the detail of protozoan cysts
What is the main reason why water should not be used to collect stool samples?
Water may destroy selected parasites
What is the recommended duration after antibiotic or anti-malarial therapy before collecting stool samples?
2 weeks
What is the main difference between the Direct Iodine Preparation and the Zinc Sulfate Flotation Technique?
The type of solution used
What is the primary purpose of the three phases of laboratory analysis in parasitic disease diagnosis?
To identify the causative agent of the disease
Why is it important for clinicians to have knowledge of the clinical manifestation of parasitic diseases?
To diagnose parasitic diseases more accurately
What is the principle of the Formalin-Ethyl Acetate Sedimentation Procedure?
Parasites are heavier than the solution and settle in the sediment.
What is the main advantage of the Trichrome stain?
It has a long shelf life and is easy to use.
What is the purpose of reviewing 300 fields under the microscope?
To confirm that the slide is negative for parasites.
What is the main difference between sedimentation and flotation techniques?
The density of the parasites compared to the solution.
What is the primary use of the Acid Fast stain?
To detect oocysts of Cryptosporidium, Isospora, and Cyclospora.
What is the advantage of using stool screening methods?
They are faster and more convenient than traditional techniques.
What is the purpose of using a commercial antibody in stool screening methods?
To detect antigen in the patient's specimen.
What is the main difference between Iron Hematoxylin and Modified Iron Hematoxylin stains?
The ability to detect acid-fast parasites.
Study Notes
Laboratory Techniques for Parasitology
- Direct Saline Wet Preparation:
- Made by mixing a drop of 0.85% saline with a small portion of unfixed stool on a glass slide
- Advantage: good recovery of most parasites and easy to perform
- Disadvantage: contains more fecal debris than floatation techniques, making it challenging for microscopists
- Direct Iodine Wet Preparation:
- Uses a single drop of Lugol's Iodine or D'Antoni's formula instead of saline
- Enhances detail of protozoan cysts (glycogen and nuclei) and kills trophozoites present
- Zinc Sulfate Flotation Technique:
- Based on differences in specific gravity, where parasites float on top and debris sinks to the bottom
- Advantage: removes more fecal debris, yielding a cleaner preparation for microscopic examination
- Disadvantage: some helminth eggs are dense and will not float
Clinical Parasitology
- Introduction:
- Parasitic diseases are a significant threat globally, prevalent in underdeveloped tropical and subtropical countries
- Climate conditions, poor sanitation, and personal hygiene practices contribute to the spread of parasitic diseases
- Importance of Laboratory Testing:
- Critical for clinicians to understand laboratory tests and clinical manifestations of parasitic diseases
- Successful laboratory identification of parasites requires knowledge and practice of laboratory testing in three phases
Stool Collection and Handling
- Stool Specimen:
- Must be collected in a clean, tight container with a tight-fitting lid
- Acceptable amount: 2.5 grams (walnut or pea size)
- Must not be contaminated with urine, as it can destroy parasites
- Interfering Elements:
- Barium, bismuth, and mineral oil can interfere with laboratory tests
- Samples from patients taking these medications must be collected 5-7 days before or after treatment
Permanent Stains
- Advantages:
- Easy to prepare
- Preserves specimen for several years
- Has long shelf life
- Disadvantages:
- Does not preserve parasite morphology adequately
- Trophozoites can't be recovered, and morphologic details of cysts and eggs may fade with time
Concentration Techniques
- Formalin-Ethyl Acetate Sedimentation Procedure:
- Most widely used sedimentation technique
- Principle: parasites are heavier than the solution and settle in the sediment of the tube
- Zinc Sulfate Flotation Technique:
- Based on differences in specific gravity, where parasites float on top and debris sinks to the bottom
This quiz covers the advantages and disadvantages of preserving protozoa morphology using permanent stains and mercury-containing preservatives. Learn about the benefits and drawbacks of different preservation methods.
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