[Elizabeth_Zeibig]_Clinical_Parasitology__A_Practi(z-lib.org)

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CHAPTER 11 The Trematodes
Phylum
Platyhelminthes
Class
Trematoda
(also referred
to as Digenea)
Intestinal Species
Fasciolopsis buski
Heterophyes heterophyes
Metagonimus yokogawai
Liver Species
Fasciola hepatica
Clonorchis sinensis
Lung Species
Paragonimus westermani
Blood Species
Schistosoma mansoni
Schistosoma japonicum
Schistosoma haematobium
FIGURE 11-1 Parasite classification: The trematodes.
include feces, duodenal drainage, rectal biopsy,
sputum, and urine. Eggs are the primary morphologic
form seen in these specimens. Under
appropriate conditions, adult worms may be
recovered. Serologic tests, such as the enzymelinked
immunofluorescence assay (ELISA), are
also available for the diagnosis of the blood
flukes (Schistosoma spp.). Representative laboratory
diagnostic methodologies are presented in
Chapter 2 as well as in each individual parasite
discussion, as appropriate.
Quick Quiz! 11-2
Adult trematodes are readily recoverable in clinical
samples. (Objective 11-5)
A. True
B. False
PATHOGENESIS AND CLINICAL
SYMPTOMS
The pathogenesis and clinical symptoms experienced
by patients infected with flukes vary by
species. Such symptoms typically correlate with
the infected area of the body, such as the intestinal
tract or lung. Symptoms associated with
trematode infections include eosinophilia, allergic
and toxic reactions, tissue damage, jaundice,
and diarrhea.
Quick Quiz! 11-3
Individuals suffering from trematode infections experience
a variety of species-dependent symptoms.
(Objective 11-6)
A. True
B. False
TREMATODE CLASSIFICATION
Like the cestodes, the trematodes belong to the
phylum Platyhelminthes. For classification purposes,
the flukes may be divided into four categories
(Fig. 11-1) based on the areas of the body
that primarily harbor the parasites: intestinal,
liver, lung, and blood.
Up until this point, an attempt has been made
to discuss the organisms individually in order
based on their classification category—that is, a
description of extraintestinal parasites follows
that of the intestinal organisms. However, the
trematodes are introduced in a slightly different
order. Because of the similarity of egg morphology
that overlaps the various classification categories,
discussion of the organ-dwelling flukes is
organized in a way that best highlights such similarities.
Primarily because of morphologic similarities,
appropriate organ-dwelling parasites are
presented as units. Similarly, the blood flukes,
which are similar in other respects, are also
described as a unit.