Parasitology Collection

What is the ideal number of samples, and when are they collected?

1. Three

2. Monday/Wednesday/Friday

Why are the three stool samples spaced out?

Because they are collected on an intermittent basis

How soon should the stool sample be examined after collection?

Within 30 mins

What form of parasite is likely to be missed if the specimen is not examined in 30 mins?

Trophozoite

What is a purged specimen?

A stool sample obtained after administration of a laxative, used to enhance detection of intestinal parasites.

What laxatives are useful for parasite purging?

1. Sodium sulfate

2. Buffered Phosphosoda cathartic

Why should purging be avoided?

Parasites do not return to the stool for a week after

Should you use enemas for collection?

No, since parasites are rarely located in the colon

What kind of parasite causes dry stool? What kind causes wet stool?

1. Dry: Cysts

2. Wet: Trophozoites

What does a chalky-white stool indicate, and what should you do with the sample?

1. Indicates patient had a barium x-ray

2. Cancel specimen because this is not acceptable.

What kind of stool does Giardia cause? Why is this?

1. Clay-colored or yellow

2. Malabsorption syndrome leading to increased fats

Where does the bleeding occur if stool is red? Where does it occur if black?

1. Red: Lower GI tract or rectum

2. Black: Higher GI tract (invasive diarrhea)

What should you do with mucus?

Test this area since organisms might be trapped. 

What other macroscopic feature should you look for?

Helminths (adult worms or proglottids may be present)

What preservative is used?

Formalin

What stain is used?

Iodine

What color does the iodine stain the cytoplasm, glycogen, and chromatin?

1. Cytoplasm: yellow

2. Glycogen: Reddish-brown

3. Chromatin: Dark brown

What is the procedure for the wet prep?

1. Scan entirety of coverslip on 10X

2. Scan 1/3 of coverslip on 40X

3. Use immersion oil as needed

What are permanently stained smears prepared from?

PVA-fixed specimens

How much of the slide (how long) should be examined in a PVA-fixed specimen?

All (15-20 mins)

How many fields should be examined under oil immersion?

10-15

What is the most common permanent stain?

Trichome

What color does Trichome stain the background?

Green

What color does Trichome stain the cytoplasm?

Blue-green tinged with purple (cysts are more purple)

What color does Trichome stain the nuclear and chromatoid structures?

Purple

What color does Trichome stain the ingested RBC’s and bacteria found in parasites?

Purplish-red

What color does trichome stain the ingested yeast in parasites?

Green

What color does trichome stain eggs and larvae?

Red

What are the three characteristics you should use to distinguish between parasites and artifacts?

1. Size

2. Cell wall

3. Internal structure

What are examples of artifacts?

1. Meat and plant fibers

2. Plant cells

3. PMN’s

4. Starch granules

5. Pollen grains

6. Other organisms

What is an ocular micrometer? 

A glass disc with an engraved scale placed within the ocular. 

What is an ocular unit based on?

The magnification

How is the value of ocular units determined?

Through calibration

How is calibration performed?

Ocular micrometer is compared with a scale of known dimensions which is placed under the various objective lenses. 

What is a micrometer?

A scale with a slide of an engraved ruler used in the calibration of the ocular micrometer

What is the value of an ocular unit for 10X?

10 micrometers

What is the value of an ocular unit for 40X?

2.5 micrometers

What is the value of an ocular unit for 100X?

1 micrometer

Amorphous particles with vegetable spiral (string beans)

Diatom (harmless organism in fresh water)

Pollen grain

Plant cell

Plant cell

Meat fiber on left with plant cell on right

Plant fiber (root hair - note strightness)

What is indicated by the arrow?

Genital primordium (distinguishing characteristic of Strongyloides stercoralis)

Cell with starch granules

Free-floating starch granules made purple by iodine

Geotrichum (a fungus not significant in human stool)

What are these? How are they formed? What do they indicate?

1. Charcot-leyden crystals

2. Breakdown product of eosinophils

3. Parasitic infection