Introduction of Stool Routine Examination
Stool Routine Examination is a very common assay and can be performed in a very simple set-up to detect the parasite in the stool such as ova, cyst, trophozoite, and larva.
Sample Collection for Stool Routine Examination
This is one of the most important steps because the reliability of the result obtained will depend largely on the care taken in the collection of the stool sample. The following points: should be kept in mind when collecting stool for the parasitological exam. Ask the patient to collect a sufficient quantity ( one teaspoonful or 100 gram approximately). Do not collect too little quantity. It may dry rapidly. Provide a suitable container such as a wide-mouth plastic pot, jar, or glass with a lid. Small matchboxes are allowed to collect. Only the solid stool. Dysentry patients with liquid stool must be given other types of containers. Screw-capped glass bottles can serve the purpose. Priority is to be given the first time to examine the liquid stool and these containing mucus or blood, because they may contain motile amoeba and die quickly in exposure to the air.
Sample Rection Criteria for Stool Routine Examination
- Never accept a small quantity of stool ( The size of a match head).
- Never collect a stool specimen in a leaf.
- Never collect a stool on a sheet of absorbent toilet paper,
- Never leave stool exposed to direct sunlight or in the air without lids.
- Never accept stool mixed with urine.
- Never place the stool container on the examination request form.
Requirements for Stool Routine Examination
- Physiological saline ( 0.85% NaCl)
- Specimen: stool
- Sterile bamboo sticks or low cone on the end of a wooden applicator stick
- Clean and grease-free slides and
- Cove slips(22- by 22-mm)
- Microscope
- Gloves
- Marker pen
Test Procedure for Stool Microscopy
- Select a clean and dry glass slide.
- Label the slide with a marker pen according to the number labelled on the sample container.
- Put one drop of normal saline in the middle of a clean and dry slide.
- Put one drop of working Lugol’s iodine solution in the middle of another clean and dry slide.
- Using a bamboo stick take a small portion ( about the size of a match-head) of s stool.
- If the stool is formed take a portion from well inside the sample.
- If the stool contains mucus and blood take the portion from the blood-stained mucus on the surface of the sample.
- Mix the portion of the stool with the drop of normal saline on the slide.
- Using an applicator stick take a second portion of the stool from the specimen and, mix with a drop of Lugol’s iodine solution.
- Place a cover slips over each form carefully to avoid the formation of air bubbles.
- Put the number of specimens on the slide with a marker.
- If the climate is hot and dry seal both preparation with Vaseline to prevent the drying out.
- Examine the preparation under the microscope at 10X and 40X objectives.
Observation
Examine the preparation under the microscope at 10X objectives starting with the top left-hand corner, to ensure that no field is overlooked, pick an object on the edge of the field of view and move the slide across the microscope stage until the objective reaches the other edge of the field, examine the field and repeat the procedure on each horizontal line. After examining 10X objectives, use 40X objectives to check the presence of protozoal parasites or to confirms the helminths.
Some of the common parasites found in the stool are-
Scientific Name Common Name
Ancylostoma duodenale – Hookworm
Ascaris lumbricoides- Roundworm
Dipylidum caninum –Dog tapeworm
Enterobius Vermicularis- Pinworm
Hymenolepis nana-Dwarf tapeworm
Nectar americans- Hookworm
Paragonimus westermani –Lung fluke found mainly in sputum
Strongyloides stercorails –Threadworm mainly larva is found in stool
Taenia saginata -Beef tapeworm
Taenia solium – Pork tapeworm
Trichuris trichuria –Whipworm
Identification features of Some common parasites encountered during Stool Routine Examination
Ova can be recognized by their specific morphology characters such as shape, size, content and colour. Some common ova and their morphology characters are described below.
Hookworm: Characteristic of hookworm ova- This ova is colourless and transparent. They are 50-60 um in size, round or oval in shape contents usually four blastomeres in the fresh stool. In the case of an old stool sample, the blastomeres may develop up to 16 or the whole of the egg is filled by a small larva, wrapped around itself, the egg is ” embryonated”.
Necator americanus ova: This ova are almost identical to that of Ancylostoma duodenale.
Ascaris Iumbricoide: Characteristic of roundworm ova (fertilized) and they are about 70 µm in size with a round shape. The two shells are distinct. The external shell is rough and brown in colour and has a single round (ovum) mass content in the centre. Unfertilized ova: This type of ova are also found in the stool, they are bigger in size than fertilized ova, more elongated (elliptical or irregular) shape. The external shell is brown and puffy, the internal shell is thin. The ova ( singular ovum) content or large round very refractile granules.
Hymenolepis nana: Characteristic of H. nana ova-They are 45-50 µm in size with a round shape. The outer layer of the shell is thin and the internal layer is thick. Content around mass with 3 pairs of hooklets inside the ova. The embryo is covered with a filamentous type embryophore.
Paragonimus westermani: Characteristic of P. westermani :- ova mainly found in sputum ( if swallowed they pass into the stools). They are about 100 µm in size, golden brown in colour, oval often slightly no one side in shape. The ova content space surround by squarish cells.
Strongyloides stercoralis (Ova) : Characteristic of Ova :- The ova is very similar to those of Ancylostoma duodenale ( Hookworm). Threadworm ova are seldom seen informed stools because they hatch before evacuation to produce the larva. They may, however, be found in liquid stools ( and occasionally in the formed stools of the carriers of certain strains). Strongyloides stercorails ( larvae): Characteristic of S.S. larva (singular):- The larvae are highly motile in the stools. They are 200-300 µm long with moderately pointed tails and short mouths. Digestive tube: easily visible, with an oesophagus, with two swelling at one end an anal pore, at the other. Genital primordium is a rounded clear shape near the middle of the larva.
Trichuris trichura (Whipworm): Characteristic of T. T. ova;- They are about 50 µm in size barrel-shaped with fairly thick and smooth shell with two layers. The eggs are orange-brown in colour. It contents a rounded, transparent plug at each pole.
Enterobius verimicularis ( pinworm): Characteristic of pinworm ova:- They are 50-60µm in size, oval, smooth, thin shell content a small granule mass in the shape of an irregular oval or the embryo of the worm, a small curled up larva with no colour and transparent.
Keynotes on Stool Routine Examination
- After examination of the stool, the smear discards it into a disinfectant jar.
- Dispose of all stool samples in a proper place.
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