[Elizabeth_Zeibig]_Clinical_Parasitology__A_Practi(z-lib.org)

CHAPTER 11 The Trematodes
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treatment of all children in moderately prevalent
areas (2 of 15 children test positive), and only
treating diagnosed cases in low-prevalence areas.
National control programs for schistosomiasis
are frequently being linked to control of other
parasitic diseases in endemic areas, especially in
sub-Saharan Africa.
Notes of Interest and New Trends
Human Schistosoma infections are predicted to
increase and spread in endemic areas because of
the establishment of water control projects on a
massive scale. Unfortunately, additional snail
breeding areas have been generated. Schistosomiasis
is now considered the second most serious
parasitic infection, only after malaria, in terms
of mortality and morbidity.
A condition referred to as swimmer’s itch has
been known to occur in persons who accidentally
become infected with the cercariae of select
Schistosoma spp., other than those discussed in
this chapter, which would otherwise infect certain
animals (mammals and birds). Human infection
is initiated following the penetration of the
fork-tailed cercariae into the skin. Severe allergic
reactions and secondary bacterial infections
may occur. The life cycle of these parasites is
not completed. Topical medications targeted at
relieving the allergic response and swelling are
available. Prevention and control measures
include controlling the snail population and preventing
the cercariae from penetrating the skin
by vigorously rubbing the body with a towel
after exposure to potentially infected water.
Quick Quiz! 11-16
The adults of this species of Schistosoma dwell in
the veins surrounding the urinary bladder: (Objective
11-5)
A. S. haematobium
B. S. mansoni
C. S. japonicum
D. All of the above
Quick Quiz! 11-17
The specimen of choice for the recovery of Schistosoma
japonicum is which of the following? (Objective
11-8)
A. Tissue biopsy
B. Urine
C. Sputum
D. Stool
Quick Quiz! 11-18
A systemic hypersensitivity reaction caused by the
presence of Schistosoma is called which of the following?
(Objective 1-1)
A. Bilharziasis
B. Katayama fever
C. Swamp fever
D. Schistosomiasis
LOOKING BACK
Laboratory diagnosis of the flukes depends primarily
on the careful microscopic examination
of stool, biliary drainage, duodenal drainage,
sputum, or urine samples for the presence of
eggs. In addition to noting the specific specimen
type, because select organisms are found in
certain samples, the organism’s size, shape, and
features (e.g., operculum, shoulders, and presence
and location of a spine) aid in identification.
It is important to stress that the eggs of certain
flukes, such as Fasciolopsis and Fasciola, are
indistinguishable and require further investigation
for speciation. Patient travel history, as well
as clinical signs and symptoms and the possible
recovery of the adult Fasciolopsis organisms, aid
in this determination. The presence of shoulders
helps distinguish Fasciola from Fasciolopsis.
Overall recovery of the adult flukes is considered
to be a rare occurrence. Nonetheless, it
is important to have some idea of their appearance.
With the exception of the schistosomes,
the flukes are basically flattened, leaf-shaped
organisms. Unlike the organ-dwelling trematodes,
the schistosomes appear much more rounded and