3_Processing Techniques

During a macroscopic examination of a stool specimen, what three characteristics are typically determined?

Consistency, color, and the presence of gross abnormalities.

What gross abnormalities are looked for during a macroscopic stool examination?

Adult worms, proglottids, pus, and mucus.

The presence of blood and/or mucus in a liquid stool specimen may suggest what condition?

Amebic ulcerations in the large intestine.

What is the primary purpose of using fixatives when collecting stool samples for parasitology?

To preserve the morphology of protozoa and prevent further development of helminths.

What is the primary goal of the microscopic examination in diagnostic parasitology?

To detect the presence of ova and parasites (O&P).

Which of the three main microscopic examination procedures should be performed on fresh specimens only?

Direct wet preparation.

What is an ocular micrometer?

A disk inserted into the eyepiece of the microscope used for measuring parasites.

What unit of measurement is used when sizing parasites with an ocular micrometer?

Microns

In the Direct Wet Preparation procedure, unfixed stool is mixed with what two possible substances on a slide?

Saline (NSS) or iodine.

In the Direct Wet Preparation procedure, what can be used as temporary stain?

lugol’s solution, d’antoni

What is the primary use of a saline (0.85% NaCl) mount in a direct fecal smear?

For the recovery and observation of motile trophozoites.

What is the effect of using an iodine mount in a direct fecal smear?

It enhances the detail of cysts but destroys trophozoites.

Results from a Direct Fecal Smear (DFS) are considered _____.

presumptive/preliminary

Under what condition is a Direct Fecal Smear (DFS) NOT required?

fixative preserved specimen

In the Kato Thick Smear technique, what is the role of glycerine?

clearing solution

In the Kato Thick Smear technique, what is the purpose of using green cellophane or Malachite green?

minimize the brightness of the microscopic field.

The Kato Thick Smear technique is primarily used for what purpose?

The quantification of helminth eggs.

What is a major limitation of the Kato Thick Smear technique?

It is not able to detect protozoan cysts or trophozoites.

What are the two main purposes of performing a concentration technique on a stool sample?

To detect small numbers of parasites and to remove debris that might mask them.

What typically happens to protozoan trophozoites during concentration procedures?

They usually do not survive the procedure.

The sedimentation concentration technique is recommended because it is efficient in recovering what type of parasite eggs?

Heavy eggs.

The sedimentation technique is best for recovering eggs from?

Schistosoma (heavy spine), operculated eggs, trematode eggs, cestode eggs, trichuris trichiura eggs, Capillaria philippinensis

What is the most widely used sedimentation technique in parasitology?

The Formalin-Ethyl Acetate Concentration Technique (FEACT).

In the FEACT procedure, what is the function of the 10% Formalin reagent?

It serves as an all-purpose fixative.

In the FEACT procedure, what is the function of Ether or Ethyl Acetate?

It dissolves neutral fats, lipids, and carbohydrates from the stool.

What is a primary disadvantage of the Formalin-Ethyl Acetate Concentration Technique (FEACT)?

The resulting sediment contains more fecal debris than a flotation technique.

List the four layers of a centrifuged FEACT tube from Top to Bottom.

1. Ether/Ethyl Acetate, 2. Debris/Fat, 3. Formalin, 4. Sediment.

What is the main advantage of flotation techniques over sedimentation techniques?

Flotation yields a cleaner preparation.

What is a key disadvantage of flotation techniques?

Some heavy eggs may not float and will be missed.

Flotation techniques are best for recovering what two general types of parasites?

Protozoan cysts and Nematode eggs.

The Zinc Sulfate Flotation technique uses a 33% Zinc sulfate solution with a specific gravity of _____ for fresh stool.

1.18

The Zinc Sulfate Flotation technique uses a 33% Zinc sulfate solution with a specific gravity of _____ for formalin-preserved specimens.

1.2

What is the risk of using a high specific gravity solution in the Zinc Sulfate Flotation technique?

distortion and shrinkage of protozoan cysts and thin-walled nematode eggs.

Which flotation technique is best for the recovery of coccidian oocysts like Cryptosporidium, Cyclospora, Cytoisospora?

Sheather’s Sugar Flotation.

What is the main reagent in the Sheather's Sugar Flotation technique?

A boiled sugar solution preserved with phenol.

What is considered the final procedure in a complete O & P examination?

permanent stains

Permanent stains are considered more reliable for confirming the presence of which type of parasite?

Protozoa (cysts and/or trophozoites).

Permanent stains allow for the detailed observation of what protozoan structures?

Intracellular organelles.

Why are permanent stains NOT the method of choice for identifying helminth eggs or larvae?

The parasites stain too dark or appear distorted.

What is the best method for detecting and identifying helminth eggs and larvae?

A concentration technique.

What type of preserved sample is the sample of choice for making a permanent stain?

PVA-preserved sample.

Before a slide is reported as negative, a minimum of _____ fields must be reviewed under OIO.

300

What is the most widely used permanent stain in parasitology due to its ease of use and long shelf life?

Wheatley Trichrome.

Which permanent stain provides clearer and sharper nuclear detail compared to Wheatley Trichrome?

Iron Hematoxylin.

The Modified Acid Fast stain is used for the detection of oocysts of which three coccidian parasites?

Cryptosporidium, Isospora, Cyclospora.

In a Modified Acid Fast stain, what color do the oocysts appear against the background?

The oocysts appear pink to red, while the background is blue.

What is the key reagent modification in the Modified Acid Fast stain compared to traditional acid-fast methods?

A weaker decolorizer (1-3% H2SO4) is used instead of acid-alcohol (HCl).

The Modified Trichrome stain is used for the detection of spores from what group of parasites?

Microsporidia.

In a Modified Trichrome stain, what color do the microsporidia spores appear?

The spores appear pink to red, while the background is green.

What is the key reagent modification in the Modified Trichrome stain for microsporidia?

The concentration of the dye is 10 times higher