Table of Contents
The parasitic infection has also emerged as a public health issue, especially in developing countries. Correct laboratory diagnosis of such parasitic infections (Parasitic Infections Lab Diagnosis) not only helps in the early treatment of the diseases but also helps to decrease hospital stays and economic burden. It includes the selection of specimens and preparations for the patients (If required, collection of the specimen, transportation, preservation, and processing too). Some parasites and their related diseases-
Avoid antibiotics or antidiarrhoeal agents, barium enema (at least 1 week ), mineral oil, bismuth, etc. prior to fecal collection. Washing of mouth during sputum collection. Use of laxatives like magnesium sulfate ( MgSO4) if required.
For better diagnosis loose stool for half an hour, semisolid for an hour, and the formed specimen can be kept for up to one day, with overnight refrigeration at 4°C but not recommended, as it may alter the morphology of parasites. Each preservative has specific limitations and no single solution enables all techniques to be performed with optimal results. The choice of preservative is also important during the concentration technique and preparation of a permanent stained smear.
Advantages-Good preservation of helminth eggs, larvae, protozoan cysts, and coccidia. It is suitable for concentration procedures, and UV fluorescence microscopy.
Disadvantages-Not suitable for trichome stain. Inadequate preservation of trophozoites.
Advantages-Both fixes and stain organisms are useful for field surveys.
Disadvantages-Not suitable for trichome stain. Inadequate preservation of trophozoites. Iodine interferes with fluorescence microscopy
Advantages-Good preservation for protozoan trophozoites and cysts. Easy to prepare permanent smear and suitable for trichome stain (both preserve organisms and make them adhere to slides).
Disadvantages-Inadequate preservation of helminths, coccidia, and microsporidia. It is also expensive and
not suitable for concentration procedures, acid-fast, safranine, and chromotrope stains.
Advantages– Suitable for both concentration procedures and preparation of permanent stained smears, acid-fast, safranine, and chromotrope stains
Disadvantages– It requires additives (e.g. albumin-glycerine) for adhesion. Permanent stains are not as good as with PVA or Schaudin’s fixative.
Advantages-Good preservation of morphology of protozoan trophozoites and cysts. Easy preparation of permanent stained smears.
Disadvantages-Good preservation of morphology of protozoan trophozoites and cysts. Easy preparation of permanent stained smears.
Advantages-Permanent smears can be made and stained with trichomes. There is lacking of mercuric chloride.
Disadvantages-Staining is not consistent. It shows poor morphology.
Advantage-Better preservative for coccidian Parasites.
A freshly prepared buffy coat blood sample is mixed with almost 2 grams of the soft fresh fecal specimen. Prepare several fecal smears and fix them immediately in Schaudinn fixative. Mix the remaining feces–buffy coat mixture in 10 ml of PVA or SAF, allow 30 minutes for fixation, and prepare several fecal smears. Stain slides by using a normal staining procedure. After staining if WBCs appear well fixed and display typical morphology it will ensure that any intestinal parasites placed in the same lot no. of preservatives would also be fixed.
In general, only preserved specimens should be shipped. The primary container of preserved fecal material is placed in a secondary container and sealed. It is then sent to the referral center by keeping it in a mailing container again after sealing and labeling. Glass slides are wrapped in shock-absorbent material or placed in a sturdy slide container. In some cases, unpreserved specimens require e.g. for the culture of microsporidium and PCR. In these cases, the specimens must be placed in clean containers quickly as possible and should be sent in cold –Packs.
Aid in determining what types of organisms may be present. Described as formed, semiformed, soft, loose, or watery. Loose or watery- trophozoites, semi-loose –cyst stages. Blood or mucus if present may also indicate amoebic dysentery, Intestinal schistosomiasis, severe trichuriasis, etc. Body fragments of adult helminths can be seen on the surface of the stool specimen by the naked eye.
Direct smear preparation helps to assess the worm burden of a patient. It provides a quick diagnosis of a heavily infected specimen. No doubt, it also checks organism motility. Unstained preparation demonstrates actively motile forms of parasites (mainly trophozoites of E. histolytica, G.lamblia, larvae of Strongyloides stercoralis, etc.) and helminthic eggs.
A minute portion of the feces is homogeneously mixed with 0.85 % sodium chloride (NaCl), and on a clean and dry slide, a coverslip is placed over it.
It is useful for the identification of cysts or dead trophozoites that also provides nuclear and cytoplasmic details.
It is useful, especially for protozoal cysts. A minute portion of feces is mixed with a drop of Lugol’s Iodine homogeneously on a glass slide, covered with a coverslip. Observation under the microscope shows-
| Structure | Result |
| Nuclei | Pale retractile |
| Cytoplasm | Yellowish |
| Glycogen material | brown color |
It demonstrates nuclei of the trophozoites of protozoa.
Reporting-In direct smear preparation protozoan trophozoites and cysts, similarly, helminth eggs and larvae may be seen which should be reported. Some artifacts or other important structures can be seen which should be reported. e.g. Charcot-Leyden crystals, RBCs, macrophages, undigested food particles, etc. Note: Formalin-preserved specimens can be used in place of saline however motility can’t be observed.
Iodine solution or any stain(e.g. buffered methylene blue) should be checked before use or periodically (once a week). Iodine should be free of any signs of bacterial or fungal contamination. The color should be that of strong tea. Human WBCs mixed with negative stool can be used as QC specimens, as the human cells stain with the same color as that seen in the protozoa.
Correct calibration of the ocular and stage micrometer of the microscope is very important because the size is an important characteristic for the identification of parasites. The use of UV fluorescence microscopy and phase contrast microscopy increases the better findings of some protozoans. e.g. coccidian parasites.
It increases the chances of detecting parasites even in small numbers that attempt to separate parasites from the bulk of fecal debris through differences in specific gravity. Various methods applied are-
Eggs and cysts heavier than the suspending liquid, become concentrated in the bottom of a tube. The most commonly used techniques are: Formalin-Ethyl-acetate sedimentation concentration: (Ritchie’s concentration method)
(for Cryptosporidium)
To the sediment, produced by standard Ritchie’s concentration, re-suspend in 5 ml deionized water and layer over 5 ml of saturated sodium chloride. Again centrifuge at 500 g for 10 minutes, oocyst concentrated in a layer just above sodium chloride while most fecal debris at the bottom. Remove 3.5 to 4 ml of the top layer. Take the remainder of the upper layer and approximately. 0.5 ml saline layer,re-suspend in 13 ml of deionized water. Centrifuge at 500 g for 10 minutes. Decant the supernatant and prepare a smear from the sediment.
(for Cyclospora)
Place 2 ml well-mixed specimen in 15 ml of 10% KOH and mix well. Allow standing for 5 minutes at room temperature. Add 8-10 ml saline and mix. Filter through 4 layers of the gauge into a clean centrifuge tube. Centrifuge at 2000 rpm for 2 minutes, decant, and discard the supernatant. Re-suspend sediment in approximately 10 ml saline centrifuge at 2000 g for 2 minutes. Decant and discard the supernatant and finally examine the sediment.
Use of a solution having higher specific gravity than the organism where the parasitic cyst and eggs having low specific gravity float on the surface. Solutions used are Zinc sulfate (ZnSO4), Sheather’s sugar, etc.
Freshly collected stool or preserved stool is mixed with 0.85 % NaCl (i.e. isotonic solution), centrifuged and re-suspend (if required), and again centrifuged. Decant supernatant fluid and re-suspend with 1-2 ml of ZnSO4. Centrifuge for 1 minute at 5000g. 2 layers will appear, from the surface take a drop of egg or cyst-rich fluid and examine.
(for Cryptosporidium)
Fecal suspension + Sheather’s sugar flotation solution. Stir vigorously. Centrifuge and examine the smear from the surface and observe with a phase-contrast microscope. Not float on a saturated salt solution: eggs of Ascaris, Taenia spp., operculated eggs of trematodes, Larvae of Strongyloides, etc. Stains are used for direct smears.
Distilled water (D/W): 100 ml
Potassium iodide (KI): 1 gm
Powdered crystals of iodine (I): 1.5 gm
D/W: 100 ml
KI: 10 gm
Iodine: 5 gm
Lugol’s Iodine: 1 part
D/W: 14 part
Lugol’s solution: 0.1 ml
Formaldehyde solution: 0.125 ml
tincture of Merthiolate: 0.775 ml
It facilitates the detection and identification of cysts and trophozoites which gives better cytological detail and confirms the findings from direct smear and smear examined after concentration. It provides laboratories to maintain a permanent record. Useful for study purposes and can be sent to a consultant for confirmation of doubt or unusual identification. A permanent smear is recommended for use with every stool specimen submitted to routine parasite examination, but the question arises how practical is it? Preparation of slides for permanent staining: a small number of faces is transferred to a clean slide with an applicator stick. The material is then streaked out in a thin, uniform film. Note: stool that does not stick properly on the slide, requires some adhesives on the slide (e.g. serum, egg albumin). Smears from fresh specimens should be placed immediately in the preservative of choice before drying.
Staining procedures most commonly used for Parasitic Infections Lab Diagnosis are-
Useful for the identification of oocysts of the coccidian parasites
Reagents–
Procedure-Prepare the smear and fix it with absolute methanol for 30 seconds. Stain with Kinyoun’s carbol fuchsin for one minute. Rinse in distilled water and drain. Destain with acid alcohol for 2 minutes. Rinse with distilled water and drain. Counterstain with malachite green for 2 minutes. Rinse in distilled water, air dry, and examine under a microscope.
Quality control-A control slide of Cryptosporidium spp. from a 10 % formalin preserved specimen should be included in each staining run. Cryptosporidium spp. stains a pinkish-red color against a uniformly green background.
It is a rapid, simple method that uniformly stains intestinal protozoa, human cells, yeast, and artifact material.
Specimen: Fresh or PVA/SAF preserved stool
Result
The cytoplasm of trophozoites: blue-green with a purple tinge.
Cyst: slightly purple
Nuclei and inclusions( RBCs, chromatoid bodies, bacteria): red
Glycogen dissolved: appears as a clear area
Background: green.
Quality control-Control slides of known protozoa such as Giardia species from PVA preserved specimens should be included with each staining run.
(for Microsporidial spore)
Chemifluorescent technique- It is useful for the detection of microsporidia and Acanthamoeba spp. It is used only for screening because It is nonspecific that other materials may also fluoresce.
Quality control: A control slide of microsporidia preserved in 10 % formalin is included with each staining run.
Baermann’s technique is useful for the concentration of Strongyloides stercoralis larvae. The technique exploits the tendency of Strongyloides larvae to migrate from solid into surrounding liquid medium when stimulated by slightly elevated temperature and then to settle to the bottom. Larvae migrated towards the bottom of the funnel and settle down on the underneath tube.
Agar Plate method -(for Strongyloides larvae)
More sensitive than Baermann and filter paper strip method.
Procedure-Take approximately 2 ml of stool and place it in the center of the culture plate. Seal it with adhesive tape and incubate at room temperature for 48 hours. Larvae migrate over the surface of agar which can be seen as tracks (Larvae of Strongyloides exhibit whip-like movement while hookworm larvae glide like snakes). Confirmation is done by a microscopic study of the washing material of the agar surface.
Schistosomal Hatching test– Feces containing viable schistosomes eggs hatched within a few hours in presence of water to miracidia larvae that migrate toward light can be observed by magnification lens on the illuminated area of the side armor water in the neck of the flask examined.
Quantitatively estimates ova which are then utilized to estimate the no. of worms infecting the patient – helpful for the treatment and follow-up.
Introduction Infection Prevention and Control (IPC) and Healthcare Waste Management (HCWM) are critical systems used…
Introduction Orientia and Rickettsia are two closely related genera of bacteria within the family Rickettsiaceae.…
Introduction A Biosafety Officer (BSO) is a technical expert responsible for the strategic and integrated…
Introduction to IHC Immunohistochemistry (IHC) is a powerful laboratory technique that combines anatomical, immunological, and…
Introduction A Tru-cut biopsy, also known as a core needle biopsy (CNB), is a minimally…
Introducton The VITEK 2 Yeast AST system is a fully automated solution for the quantitative…
View Comments
I do not even know how I ended up here, but I thought this post was great. I don't know who you are but certainly you are going to a famous blogger if you are not already ;) Cheers!
I appreciate you sharing this blog post.Really looking forward to read more.
Hey there, I think your blog might be having browser compatibility issues. When I look at your blog site in Chrome, it looks fine but when opening in Internet Explorer, it has some overlapping. I just wanted to give you a quick heads up! Other then that, superb blog!