Page 45 - parasitology for medical and clinical laboratoryprofessionals

Epidemiology and Conditions Leading to Parasitic Infestations 25

DIAGNOSING PARASITIC
INFECTION
Diagnosis usually includes a stool examination obtained
by routine methods, the aid of a bulk-producing laxative,
or mechanical removal of the stool specimen from con-
stipated individuals. The test for parasites from the intes-
tine utilizing fecal matter is called the “O&P,” indicating
that both the ova (eggs) and the parasites may be found.
Unfortunately, these procedures lack sensitivity, meaning
that they yield a high rate of false negatives. Although the
appearance of the parasite eggs is characteristic of the
species, it is sometimes a problem in differentiating some
Source: Centers for Disease Control and Prevention (CDC) Stool and Rectal Mucosa
species by this method. Also, different labs may have dif-
ferent parameters for determining a parasitic infection.

Examinations

Although stool examinations are the most common manner
of diagnosing intestinal parasite infections, the most reliable
but least convenient is that of a rectal mucosal examina-
tion to directly find the parasite or eggs (ova) of the para-
site. The rectal mucosal surface becomes tender and more
FIGURE 2-11 Nigerian woman drinking water
delicate, easily bleeding in the quite large expanse of tissue
directly from a local pond through a pipe filter
in the region which provides a large amount of mucous
secretion. In addition, a rectal mucus swab may be useful
for collecting parasites and detecting a parasitic infection
in many rural areas. Secondly, when travelling to certain
by which the mucous membranes are firmly swabbed and
parts of the world, the visitor is often exposed to greater
the specimen is placed on a slide for staining before a direct
amounts of parasites than the body is able to handle.
identification can be performed. Other lab tests to enhance
You will often see the people living in these areas who
the diagnosis of a parasitic infection include a sedimenta-
do not become infected or at least show no symptoms,
tion procedure for concentrating the organisms or the eggs
even though sanitary practices related to water sources
from a fecal specimen where applicable for certain species.
and food handling are inadequate. Their bodies have
developed the immune systems to a point that enables
them to avoid becoming inhabited by intestinal parasites DIRECT TESTING FOR PARASITES
by acquired immunity. The third common way to con-
tract infections is exposure to foods from restaurants and Although the most straightforward way to diagnose par-
street vendors where food handlers may be carriers but asites is with microscopic examination for either or both
show no signs of illness. Even though the human body ova or more rarely the parasite itself, specific identifica-
mounts a strong reaction to parasites upon becoming tion is becoming more readily available with direct tests
infected, the disease is not cured unless medication is for the antigens (usually proteins) of parasites. Some
administered to eliminate the organisms. Sometimes the parasites may be specific to the blood for certain bodily
level of parasites in an infected person may diminish to tissues but the most prevalent parasites are found in the
the point that few symptoms or signs may be visible al- human intestine. As with any micro-evaluation of body
though transmission of the disease by these persons may samples, such as with fecal specimens, this also relies on
still occur. the laboratory professional’s skill and diligence in picking