Page 46 - parasitology for medical and clinical laboratoryprofessionals

26 CHAPTER 2

out the proverbial needle from the haystack. This is true Lymph biopsies are used in some cases to detect
whether looking for and finding filarial (small wormlike toxoplasmosis caused by a protozoan called Toxoplasma
organisms), eggs, and protozoa or other manifestations gondii. The realm of parasitology that involves the study of
of parasites from blood and other specimens. tissue sections is not medically indicated as frequently in
When some groups of parasites are suspected, such the United States as in other countries. Entire textbooks are
as Entamoeba, roundworm, hookworm, Strongyloides, devoted to studies of tissue parasites and are often included
and Pneumocystis jirovicii, it is possible to perform tests in a specialty called tropical medicine. Technologists and
with sputum specimens to establish that an infection technicians do not ordinarily perform these tests, although
is present. Initially, P. carinii (now chiefly reported as they may prepare and stain the specimens for microscopic
P. jirovicii) was thought to be the cyst form of a parasite. examination, particularly those technical personnel called
Some parasites, particularly roundworms, are found in the histotechnologists. These tests are often performed by
lungs during part of their life cycle and cause symptoms of doctoral scientists and pathologists from stained tissue
bronchitis and even asthma. This cycle of reproduction specimens removed from the body surgically. Although
involves coughing up of the larvae and then they are rou- the organism has a complex life cycle, the diagnostic stage
tinely swallowed with saliva and mucous and continuously is most often made by microscopic examination of tissues
repopulate the digestive tract. The cycle is repeated as they stained with hematoxylin and eosin (H&E).
reproduce and begin their migration to the lungs again.
Even the urine may be a viable specimen for finding some
parasites as some organisms identified as blood flukes can
be diagnosed through urine sediment examination. Urine MICROSCOPIC DIAGNOSTIC
samples are used for testing for certain microfilaria and
particularly for Trichomonas vaginalis infections. FEATURE
Swabbing the perianal area can often detect pin-
worms, which are most often found in small children.
General
Pinworms are often discovered when the child complains Classification Sporozoan
of itching or is seen to frequently scratch the anal region.
Pinworms are most often diagnosed by the peculiarity of Organism Toxoplasma gondii
their eggs, and they are rarely found with either a purge Specimen Required Tissue biopsy speci-
or other rectal procedures. These organisms come out of men (for direct
examination)
the anus at night to lay their eggs, and the eggs are most
often found by using a Scotch-tape prep of the perianal Stage Cyst stage is
diagnostic
area obtained before daylight while the child is still some-
what sleeping. This procedure may also recover eggs of Size Tissue cysts in the
brain often sphe-
the beef and the pork tapeworms as well as blood flukes.
roidal and reach a
Sometimes scrapings of the perianal area will also reveal
diameter of 70 μm;
amoebae infections. All of the major parasites that invade
intramuscular cysts
the human body will be discussed at length, along with elongated and may
methods of identification, in the chapters of this book. be up to 100 μm long
Due to some parasites that imbed themselves in tis- Shape Often crescent-shaped
sues where they prefer to live, detection is often not possible
Motility Gliding movement for
without some sort of invasive procedures. Muscle biopsy invading the host cells
can reveal the pork tapeworm or trichinella, the latter which
Nucleus(i) Prominent and
migrates into muscle tissue. Rectal biopsy can reveal flukes, most often situated
and liver biopsies are used for visceral larva migrans. Hydatid centrally
(clear) cysts should have a biopsy (tissue sample surgically Cytoplasm No remarkable char-
excised) to determine the type of tapeworm that inhabits acteristics; organelles
the cyst. Needle biopsy can show heartworms on rare occa- with envelopes
sions in the lungs of humans (often a single worm of Difilaria Other Features None
immitis is found in humans) as well as Pneumocystis jiroveci.