STEP 9: Carefully tear out the hindgut. Slice it longitudinally and mount it on a slide.
Microscopically, search the entire hindgut carefully for presence of crithidial
and metacyclic trypanosomal forms.
(4) It is necessary to keep in mind that xenodiagnosis gives a variable
percentage of positivity and that not all reduviids fed on diseased persons become
infected.
Section III. GASTROINTESTINAL TRACT SPECIMENS
2-14. INTRODUCTION
In humans, the site most frequently infected by parasites is the intestinal tract.
Therefore, a great deal of emphasis must be placed on the collection, fixation, and
examination of specimens from the gastrointestinal tract.
2-15. COLLECTION OF GASTROINTESTINAL TRACT SPECIMENS
Specimens should be collected and handled in such a manner that they arrive at
the laboratory in good condition for the identification of protozoans and helminths.
Frequently, intestinal parasites are diagnosed or ruled out based on examination of fecal
specimens. However, perianal swabs, liver and duodenal aspirations, or duodenal
contents may also be received for examination of intestinal parasites.
a. Fresh Specimens. Laboratory and nursing personnel are responsible for
instructing the patient on the proper and correct procedure to be used in the collection of
the stool samples. Water and urine will destroy the trophozoites and, when soil
contaminates the stool, free living parasites may give a false positive result. Therefore,
care must be taken to avoid contaminating the sample with water, urine, or soil.
(1) Number of samples. Recovery of intestinal parasites is enhanced by the
collection of three or more specimens at intervals of two to three days apart. The time
period between the collection of samples is necessary to compensate for the periodicity
of the life cycles of the parasites.
(2) Specimen containers. The most suitable container for collection and
transportation of stool specimens is one that has a wide leakproof cup, bottle, or carton
that is clean and dry. This container should not be reused. It should be disposable.
(3) The label. Certain information should be affixed to the container to
prevent the mixing of samples.
(a) Patient data. The name of the patient must be clearly written on the
container. Other information which should be on the label includes the patient's
identification or hospital number, the ward or clinic name, and the name of the attending
physician.
MD0841
2-28
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