Diagnostic Parasitology Flashcards
Ova refers to
Egg stage of the parasite
Procedure for stool specimen
Ova and Parasite
The typical stool collection protocol consists of ____ specimen.
3 specimen
Microscopic examination consists of three possible
components:
○ Collection
○ Transport
○ Fixatives
How was the 3 specimen collected?
One specimen collected every other day or a total of three collected in 10 days
In cases of Amebiasis, how it was collected?
six (6) specimens in 14 days is acceptable.
Stool samples from patients undergoing therapy that
include:
○ Barium
○ Bismuth or mineral oil
○ Antacids
○ Laxatives
● Should be collected ______________
Prior to therapy or not until 5-7 days after the completion of therapy.
Antibiotics and antimalarial medications
○ Should be _____________
Delayed for two (2) weeks following therapy.
Temporary storage of fecal samples in a refrigerator _________ is acceptable.
(3 to 5°C)
The recommended time for liquid stool is
Within 30 minutes of passage
Semi-formed stool should be examined
within 1 hour of
passage.
Formed stool specimens can be held for ______ following collection.
24 hours
Stool container should be in
Clean, wide-mouthed containers made of waxed
cardboard or plastic, watertight with a tight-fitting lid
how many grams is the acceptable amount of stool required for
parasite study,
2-5 grams
SPECIMEN CONTAINER LABELS
○ Patient’s name and Identification number
○ Age and Sex
○ Physician’s name
○ Date and Time of Collection
○ Other information:
■ Suspected diagnosis
■ Travel History
■ Clinical Findings
Are substances that preserve the morphology of
protozoa and prevent further development of certain
helminth eggs and larvae.
Fixatives
the ratio of fixative to stool specimens.
3:1 ratio
The specimen must be fixed in the preservative for at
____________ before processing begins.
least 30 minutes
○ Most commonly used fixative.
○ All-purpose fixative for the recovery of protozoa and
helminths.
○ May be routinely used for direct examinations and
concentration procedures, but not for permanent
smears.
Formalin
Two concentrations of formalin are commonly used
■ 5% concentration ideally preserves protozoan cysts
■ 10% concentration preserves helminth eggs and larvae
○ Comprised of a plastic powder that acts as an
adhesive for stool specimens when preparing slides
for staining.
○ Most often combined with Schaudinn solution, which
usually contains zinc sulfate, copper sulfate, or
mercuric chloride as a base.
Polyvinyl Alcohol (PVA)
Advantages of PVA
■ Can be used for the preparation of permanent
stained smears.
■ Long shelf life when stored at room temperature.
○ Contains merthiolate (also called thimerosal) and
iodine which act as staining components, while
formalin acts as preservative.
○ Useful for the fixation of intestinal protozoans,
helminth eggs, and larvae.
Merthiolate-Iodine Formalin (MIF)
○ Can be used for performing concentrations
techniques and permanent stained smears.
○ Only requires a single vial and it is mercury-free.
Sodium Acetate Formalin
○ Free of formalin and mercury.
○ Can be used for concentration technique and
permanent stained smears.
Alternative Single-Vial System
Macroscopic Examination
Color
Consistency
Gross abnormalities
Microscopic Examination
○ Three (3) distinctive procedures
■ Direct wet preparations
■ Concentrated techniques
■ Permanently stained smear
ELEMENTS WHICH MAY FOUND IN STOOL SPECIMENS
- White blood cells
- Red Blood cells
- Macrophages
- Charcot Leyden crystals
- Epithelial cells
- Eggs or arthropods, plant nematodes and other spurious parasites
- Fungal spores
- Elements of plant origin which resemble some parasites include:
- Plant and animal hairs may loo like helminth larvae
In actual practice, one can mistake the active macrophages for
Ametic trophozoites
○ Used to measure objects observed microscopically
accurately.
○ Is a disk that is inserted into the eyepiece of the
microscope.
○ Diagnostic stages of parasites detected
microscopically are measured in units known as
microns
○ Calibration is necessary
Ocular Micrometer
○ Also known as direct wet mount
○ Slide may by mixing a small portion (2g) of unfixed
stool with saline or iodine
○ Under the microscope, the presence of motile
protozoan trophozoites is being detected
Direct wet preparation
The reagent choice for direct wet preparation
0.85% saline solution
Trophozoites can be stained to demonstrate the
nuclear morphology using
Nair’s buffered methylene blue solution (BMB)
○ Take a small quantity of stool sample.
○ Transfer onto 2 spots on a glass slide.
○ Add 1 drop of saline solution on one spot and 1 drop
of iodine solution on the other spot.
○ Cover the 2 drops with 2 cover slides and read the
preparation under the microscope.
Direct fecal smear
○ May be made to enhance the detail of the protozoan
cysts
○ Lugol’s D’Antoni’s formula (drop of iodine)
Direct wet Iodine preparation
○ Useful in detecting eggs with thick shells such as in
Ascaris and Trichuris.
○ Not eggs with thin shells (hookworms)
○ If the preparation is too long before the examination,
hookworm eggs become too transparent or distorted
making identification very difficult.
○ Not for protozoan cysts and trophozoites
Kato-Thick Smear
○ Provide the ability to detect small numbers of
parasites that might be detected using wet
preparations.
○ Aggregate the parasites present into a small volume
of the sample.
○ Can be performed on fresh or preserved stool
specimens.
○ Trophozoites DO NOT usually survive the procedure.
Concentration methods
Two types of concentration methods:
Sedimentation and Floatation
○ Most widely used sedimentation technique.
○ Based on specific gravity.
○ Ethyl acetate is added to a saline-washed
formalin-fixed sample and the tube is then
centrifuged.
Formalin-Ethyl Acetate Sedimentation
Advantages and Disadvantages of Formalin-Ethyl Acetate Sedimentation technique
○ Advantages:
■ It provides good recovery of most parasites
■ Easy to perform
○ Disadvantages:
■ The preparation contains more fecal debris than
a flotation technique