Medical Parasitology Lab

Artifacts

Definition Artifacts: other things, living or artificial, present in

the stool that are not parasites and could mislead the laboratory worker.

Note: “Artifacts not to be mistaken for cysts”.

Blastocystis• Round or oval,

sometimes with angular irregular edges, contain one large vacuole taking up almost the whole cell, the compressed cytoplasm forms a granular ring round it.

Blastocystis

Yeast • Oval, often with buds,

often contain eccentric cluster of 3-6 small granules.

• Some related forms of yeast are rectangular, with a very clear oval cytoplasm inside: arthrospores.

Yeast

Yeast in an iodine-stained concentrated wet mount of stool. Yeast in wet mount may be confused for Giardia lamblia cyst.

Yeast Giardia lamblia cyst

Leukocytes • Round or slightly elongated,

with an irregular outline.• Contain refractile cytoplasm,

clear and granular with tiny vacuoles.

• Nucleus indistinct, sometimes with a star- shaped false karyosome.

Pus • Pus can be seen by the

naked eye as opaque, greyish streaks ( not transparent like mucus).

• Under the microscope it appears as a mass of more or less degenerate leukocytes

Bacteria

Coccidia • These are protozoa that may be parasite of men without

causing any significant pathogenic effects, or may be found in transit in stool following the consumption of infected foods.

• They appear in stool in a form resembling cyst called oocysts or sporocysts.

• An elongated oval, sometimes tapered at one pole.• There three types:

a. 4 sporozoites (small banana shaped rods), each containing a small round nucleus, sometimes a few large granules massed at one pole.

b. One large round granular cell.c. Refractile granules completely fill the interior.

Coccidia (cont.)

Coccidia (cont.)

Air bubbles

Oil droplet

Fungal spores

Fungal spore in a wet mount of stool.  Such spores may be confused for the cysts of Entamoeba spp.

Fungal spore Entamoeba histolytica/dispar cyst

Plant fiber

Strongyloides stercoralis larvae

Misdiagnosis can lead to improper treatment

Hair fiber

Plant cellMay confused with helminthes eggs

Plant cell

• Plant material in an iodine-stained concentrated wet mount of stool.

This material can be confused for a hookworm egg

Charcot-Leyden crystals

Epithelial cells

Macrophages

RBCs

Pollen grains

Pollen grains

Starch granules

Crystals

Non- parasitic structure found in stool Non parasitic objects may be misidentified as parasites. The

differentiation of the most common pseudoparasites is as follow:1. Protozoan cyst: may be confused with air bubbles, fat globules or

yeasts. • Iodine should be added to the wet preparation so that the internal

structure of the cyst is stained and identifiable.2. Amoebic trophozoites: must be differentiated from non- pathogenic

protozoan trophozoites and macrophages.• Trophozoites of Entamoeba histolytica/dispar must be motile and

hematophagus.• Macrophages found in cases of intestinal amoebiasis are

distinguishable from amoebic trophozoites by possessing a larger nucleus and, although they can haematophagus, they are only motile for a very short time. Their pseudopodia are small, blunt and granular.

Cont. 3. Ova, their general shape, except for Entrobius, is

perfectly symmetrical, distinguishing them from various objects found in stools.

4. Trichuris and Taenia ova may be confused with pollen grains.

5. Ascaris ova may be confused with vegetable cells, the latter having smooth, thick walls but irregular shape.

6. Strongyloides or hookworm larvae can be confused with hair or vegetable fibers. The latter are usually tapered at one end and the other being blunt and with no internal structure.

• Free living nematode larvae may be found in concentrates if contaminated water is used

7. Fasciola ova resemble vegetable cells.8. Insect and may be found in stools as spurious

infection. Mite eggs may be confused with hookworm eggs.

9. Dipylidium caninum eggs sacs can look similar to vegetable cells.

10.Other structure found in stool are crystals, Charcot- Leyden are the breakdown products of eosinophil cells and may be present in stools or sputum.

11. Starch granules are sometimes seen in stool. When undigested, they appear as concentric rings and stain blue with iodine, when partially digested, they stain red.

Cont.

Intestinal Protozoa

Raed Z. Ahmed, Medical Parasitology Lab.,2012

Giardia lamblia

Giardia lamblia• It is the most common flagellate of the intestinal tract that cause

giardiasis, Traveler's diarrhea.• There is two diagnostic stages for Giardia lamblia :

1. Cyst is oval measuring 11 – 14u in length and 7 to 10 µm in width with 4 nuclei and remnant flagella, and it’s the infective stage.

2. Trophozoite is described as having a 'tear-drop' shape and are 10 to 20 µm long and 5 to 10 µm wide. The trophozoites contain two nuclei, four pair of flagella. (motility by flagella).

• Diagnosis:• Stool examination to see cyst stage, or trophozoite stage if

the sample is fresh.

Life cycle

Giardia lamblia cyst

Giardia lamblia cyst

Giardia lamblia Trophozoite

Giardia lamblia Trophozoite