[Elizabeth_Zeibig]_Clinical_Parasitology__A_Practi(z-lib.org)

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CHAPTER 2 Specimen Collection and Processing
discussion of these and of all histologic methods
mentioned in this chapter is beyond the scope
of this text.
Sputum
Sputum is typically collected and tested from
patients suspected of being infected by the lung
fluke Paragonimus westermani (Chapter 11).
Patients with Strongyloides stercoralis (Chapter
8) hyperinfection will demonstrate motile larvae
in their sputum. Other parasitic infections that
may be found in sputum samples include microsporidia,
E. histolytica, Entamoeba gingivalis
(Chapter 3), Ascaris lumbricoides, and hookworm
(Chapter 8). An early-morning specimen
is best and should be collected into a widemouthed
container with a screw cap lid. Saliva
should not be mixed with the specimen. The
sample may then be examined directly via wet
preps and/or concentrated using N-acetylcysteine
or other appropriate agent. Microscopic examination
of the sediment can include wet preps and
permanent stains.
Urine and Genital Secretions
Urine is the specimen of choice for the detection
of Schistosoma haematobium (Chapter 11) eggs
and may also yield Trichomonas vaginalis trophozoites
(Chapter 4). Microfilariae can sometimes
be found in the urine of patients with a
heavy filarial infection. The specimen should be
collected into a clean container with a watertight
lid. The sample should be centrifuged on arrival
at the laboratory. Microscopic examination of
the sediment should reveal the parasites, if they
are present.
Vaginal and urethral specimens, as well as
prostatic secretions, are typically collected and
examined for the presence of T. vaginalis trophozoites.
These specimens may be collected on a
swab or in a collection cup equipped with a lid.
Saline wet preparations are the method of choice
for demonstrating the motile trophozoites.
Prompt examination of these preps is important
because it helps ensure the recovery of the
delicate organism. Permanent stains may also be
used if desired.
Alternative techniques for the diagnosis of
T. vaginalis include antigen detection methods
using latex agglutination and EIA procedures.
A commercially available nucleic acid probe
is also available. Culture methods are available,
including a commercial product that uses a
culture pouch. All these methods are highly
successful for diagnosing this sexually transmitted
parasite.
Eye Specimens
Acanthamoeba keratitis (Chapter 3) is best diagnosed
by the collection and examination of
corneal scrapings. These scrapings should be
placed into an airtight container. It is important
that small tissue samples be kept moist with
sterile saline. Other specimens that may be tested
include a contact lens or contact lens solution.
The samples may be processed in several ways.
First, it may be cultured on an agar plate seeded
with gram-negative bacteria. Examining the
culture plate under low dry magnification every
day for 1 week should reveal the trophozoites
(usually in less than 4 days) and the cysts (in 4
to 5 days). Second, the scrapings may be transferred
to glass slides and stained using the calcofluor
white stain, followed by microscopic
examination using fluorescent microscopy. The
Acanthamoeba cysts stain apple green. It is
important to note that this technique does not
stain the trophozoites. Third, the scrapings may
be processed using histologic methods.
In addition to Acanthamoeba, T. gondii,
microsporidia, and Loa loa (Chapter 9) are also
potential eye pathogens. These may be detected
with histologic stains and specialized culture
methods.
Mouth Scrapings and
Nasal Discharge
Mouth scrapings are the sample of choice for the
detection of E. gingivalis and Trichomonas tenax
(Chapter 4), whereas nasal discharge specimens