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Molecular
Diagnosis
Microscopic
examination is still considered the “gold standard” for the diagnosis of
parasitic diseases. If an unequivocal identification of the parasite
can not be made, the stool specimen can be analyzed using molecular
techniques such as polymerase chain reaction (PCR). PCR amplified
fragments can be analyzed by using restriction fragment length
polymorphisms (RFLP) or DNA sequencing if further characterization is
needed.
Specimen
Collection
If PCR is being requested on a stool specimen, the specimen must be
collected in absence of preservatives kept and shipped either refrigerated
(4°C) or frozen (shipped with dry ice). Alternatively stool specimens can
also be mixed in potassium dichromate (1:1 dilution with 5% w/v) or in
absolute ethanol (1:1 dilution) and shipped refrigerated. Trichrome
stained smears (for G. lamblia or E. histolytica/dispar)
or acid-fast smears (for C. parvum or C. cayetanensis)
should accompany the stool specimen when requesting PCR for any of these
protozoa. All stained smears will be read first and if an identification
of the parasite can be made, PCR will not be performed. PCR results take
approximately a week for completion. Click here for more information
about shipping stool specimens to CDC.
It is necessary to extract DNA from the stool specimens for PCR detection. Click to view the DNA extraction protocols recommended for molecular diagnosis of intestinal parasites.
PCR
Analysis
PCR detection of
Giardia lamblia,
Cryptosporidium sp.,
Cyclospora
cayetanensis,
microsporidia spp., and
Entamoeba
histolytica/dispar is performed at CDC. DNA preparations
extracted from fecal samples are tested by PCR with diagnostic primers and
the amplified DNA fragments are electrophoretically resolved on a 2%
agarose gel for analysis of results. Click on the links above to
view analysis of PCR results for the respective parasites listed.
For additional information on molecular diagnosis using stool specimens, call the Division of Parasitic Diseases at 770-488-4072
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