Examination of faeces for parasites Medical Parasitology
Slide 2
Collection of faecal specimen The administration of drugs or
anti-diarrheal substances such as mineral oil, barium, bismuth,
magnesium and antibiotics should be terminated at least one week
before stool collection. These substances may interfere with the
ova and parasite examination by reducing the visibility of
organisms. Stool sample should be collected in a clean dry
container. Stool sample should not be contaminated with urine,
water or any other fluids.
Slide 3
A good stool specimen is one that has been sampled from areas
containing blood, mucous and areas of loose or watery consistency.
One of the most important steps is the mixing of the stool with
fixative. The purpose of fixative is to preserve the morphology of
the parasites. The trophozoite stage is a very fragile stage and
chances for recovery are increased when the stool is fixed
completely and as quickly as possible.
Slide 4
Three stool specimens collected on alternate days is
recommended as the standard for the ova and parasite examination.
Recently, one specimen properly collected, fixed and examined for
the proper length of time will yield 90% of the intestinal
parasites present. A second and third specimen will yield 8% and 2%
respectively.
Slide 5
Slide 6
1 st stool examination Negative for parasites + Asymptomatic
patient No need for the 2 nd & 3 rd stool examination Negative
for parasites + Symptomatic patient 2 nd & 3 rd stool
examination is recommended
Slide 7
Collection of stool sample in children: a.For children in
diapers, line the inside of the diaper with plastic wrap, to
prevent the diaper from absorbing the stool. b.For older children,
put plastic wrap, newspaper, or a special collection container
under the toilet seat to catch the stool. Never take the sample out
of the water in the toilet bowl and do not allow urine to touch it.
If the child urinated at the same time, do not collect this stool.
Toilet water and urine will destroy the germs or parasites.
Stool analysis Macroscopic examination: 1. Colour: normally
brown 2. Consistancy: Formed, semi formed or watery 3. Odour:
offensive 4. Reaction: normal stool PH is 7.0-7.5 5. Presence of
:Blood, mucus, pus, fat. 6. Parasites: adult worms or worm
segments. Microscopic for: 1.RBCs 2.Pus cells 3.Bacteria
4.Parasites: helminthic ova or protozoal infecction.
Slide 11
Parasites that can be found in stool specimen Helminthes I.
Adult worms 1. Entrobius vermicularis. 2. Ascaris lumbericiodes. 3.
Mature and gravid segments of Taenia saginata.
III. Intestinal protozoa: 1. Entamoeba histolytica trophoziotes
and cysts. 2. Gardia lamblia trophoziotes and cysts. 3. Balantidium
coli cysts. 4. Cryptosporidium oocysts. 5. Isospora oocysts
Slide 14
Examination of faeces for helminthes eggs and intestinal
protozoa 1. Direct smear method. 2. Iodine smear method. 3.
Concentration methods.
Slide 15
Direct smear method Small amount of stool is emulsified in one
drop of saline on a microscopic slide and covered with a cover
glass, then examined microscopically. Using a piece of stick or
wire loop, mix a small amount of fresh specimen (especially mucus
and blood) with each drop. Cover each preparation with a cover
glass.
Slide 16
Too much stool one drop of saline on a microscopic slide Small
amount of fresh specimen by wooden stick Emulsify
Slide 17
Avoid air bubbles Press cover slip slightly, remove excess
liquid with paper towel
Start with the scanning low power x4 objective lens and then
higher powers for more details. use X100 lens for protozoa. Examine
the preparations using the 10 and 40 objectives with the condenser
iris closed sufficiently to give good contrast. Look especially for
motile E. histolytica trophozoites containing red cells, motile G.
lamblia trophozoites, motile Strongyloides larvae,. the Look for
eggs and cysts of parasitic pathogens.
Slide 20
It should be noted that: 1. In cases of parasites of large
intestine like Schistosoma mansoni, eggs are deposited on the
surface of the formed faeces and not mixed with the faecal mass as
in eggs of parasites living in small intestine. 2. In case of
protozoa: Living trophoziotes can be detected by their movement.
The addition of iodine solution stains the nuclei and glycogen
vacuoles making identification easier.