Must Know in Diagnostic Procedures in Parasitology
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Course
Clinical Parasitology
Institution
Centro Escolar University
Book
Clinical Parasitology
The document includes:
- Table summary of diagnostic procedures to detect parasites
- Definitions and procedures about diagnostic procedures
- Stool specimen requirements (how to preserve, etc.)
- Stages of parasites found in specimens (stool, urine, duodenal aspirate, sputum, blood, CSF)
Must Know in Cestodes (Tapeworms): Clinical Parasitology
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Clinical Parasitology
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DIAGNOSTIC PROCEDURES: PARASITOLOGICAL SPECIMENS
SPECIMEN PARASITE & THEIR STAGE SPECIMEN PARASITE & THEIR STAGE
Ova of INTESTINAL HELMINTHS like
Ascaris lumbricoides; Trichuris trichiura Ova of Paragonimus westermani
STOOL Capillaria philippinensis ; Necator SPUTUM
americanus Trophozoite of Entamoeba histolytica
Ancylostoma duodenale
Filariform larva of Necator americanus and
Schistosoma mansoni and Schistosoma Ancylostoma duodenale
japonicum
Diphyllobothrium latum Larva of Ascaris lumbricoides
Taenia solium and Taenia saginata
Rhabditiform Larva of Strongyloides
stercoralis
Cyst & Trophozoite stages of Entamoeba
histolytica, Giardia lamblia & Balantidium
coli
Oocyst of Cryptosporidium parvum
URINE Ova of Schistosoma haematobium BLOOD Ring form trophozoites & gametocytes of
Trophozoite of Trichomonas vaginalis Plasmodium spp and Babesia microti
Microfilaria of Filarial worms like Wuchereria
bancrofti ; Brugia malayi ; Loa loa
DUODENAL Trophozoite of Giardia lamblia CSF Naegleria fowleri and Acanthamoeba spp.
ASPIRATE
STOOL SPECIMEN
o parasites are often shed (i.e., enter and subsequently passed in the stool) intermittently, they may not
appear in a stool specimen on a daily basis; therefore, multiple specimens are recommended for
adequate detection.
o The typical stool collection protocol consists of three specimens, one specimen collected every other day
or a total of three collected in 10 days. One exception is in the diagnosis of amebiasis in which up to six
specimens in 14 days is acceptable
o medications and substances may interfere with the detection of parasites. Stool samples from patients
whose therapy includes barium, bismuth, or mineral oil should be collected prior to therapy or not until
5 to 7 days after the completion of therapy. If the samples are taken during the course of therapy, these
interfering substances may mask possible parasites during examination.
o Collection of specimens from patients who have taken antibiotics or antimalarial medications should be
delayed for 2 weeks following therapy.
o Stool specimens should be collected in a clean, watertight container with a tight-fitting lid. The
acceptable amount of stool required for parasite study is 2 to 5 g, often referred to as the size of a
walnut.
o Urine should not be allowed to contaminate the stool specimen because it has been known to destroy
some parasites. Stool should not be retrieved from toilet bowl water because free-living protozoa and
, nematodes may be confused with human parasites. In addition, water may destroy select parasites, such
as schistosome (eggs and amoebic trophozoites.
o Toilet paper in the stool specimen may mask parasites or make examination of the sample difficult
o The specimen container should be labeled with the patient’s name and identification number, the
physician’s name, and the date and time of sample collection
o To demonstrate the motility of protozoan trophozoites, a fresh specimen is required. The trophozoite
stage is sensitive to environmental changes and, on release from the body, disintegrates rapidly.
o Other parasite stages (e.g., protozoan cysts, helminth eggs and larvae) are not as sensitive and can
survive for longer periods outside the host. Because trophozoites are usually found in liquid stool, it is
recommended that liquid specimens be examined within 30 minutes of passage.
o In keeping with stool consistency, semiformed specimens may yield a mixture of protozoan cysts and
trophozoites and should be evaluated within 1 hour of passage.
o Formed stool specimens are not likely to contain trophozoites; therefore, they can be held for 24 hours
following collection. If these guidelines cannot be met, the specimen should be placed into a
preservative.
PRESERVATION
o If the stool is to be processed within 1 hour, it may be stood at room temperature. Beyond one hour,
the stool must be refrigerated (3-5degC for 4 hours). Hookworm eggs mature and hatch if allowed to
remain at room temperature & may be confused with Strongyloides stercoralis larvae. Formed stools
may be refrigerated 1-2 days if examination is delayed although this will not guarantee recovery of all
parasites. Never Freeze the sample. Trophozoites from a refrigerated stool can regain motility in warm
saline on a warm slide. Never keep stool samples in the incubator. 37 degC beyond 30 minutes destroys
amoeba.
STOOL PRESERVATIVE/FIXATIVES:
o The ratio of fixative to stool is important for the successful recovery of parasites and, whatever fixative
is used, the recommended ratio is three parts fixative to one-part stool.
o The specimen must be fixed in the preservative for at least 30 minutes before processing begins
FORMALIN POLYVINYL ALCOHOL
o Formalin has been used for many years as an all- o is comprised of a plastic powder that acts as
purpose fixative for the recovery of protozoa and an adhesive for the stool specimen when
helminths. preparing slides for staining.
o Two concentrations of formalin are commonly used; a o PVA is most often combined with Schaudinn
5% concentration ideally preserves protozoan cysts solution, which usually contains zinc sulfate,
and a 10% concentration preserves helminth eggs and copper sulfate, or mercuric chloride as a base.
larvae. o Trophozoites and cysts of the protozoa, as
o Formalin may be routinely used for direct well as most helminth eggs, may be detected
examinations and concentration procedures, but not using this fixative.
for permanent smears. o it can be used for preparation of a permanent
o There are three primary advantages for the use of stained smear. PVA-preserved specimens have
formalin: (1) it is easy to prepare; (2) it preserves a long shelf life
o when stored at room temperature.
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