[Elizabeth_Zeibig]_Clinical_Parasitology__A_Practi(z-lib.org)

242
CHAPTER 10 The Cestodes
Phylum
Platyhelminthes
Class
Cestoda
Intestinal Species
Taenia saginata
Taenia solium
Hymenolepis diminuta
Hymenolepis nana
Dipylidium caninum
Diphyllobothrium latum
Intestinal-Extraintestinal Species
Echinococcus granulosus
FIGURE 10-1 Parasite classification: The cestodes.
PATHOGENESIS AND CLINICAL
SYMPTOMS
Many patients infected with intestinal cestodes
remain asymptomatic. However, infected persons
who experience symptoms often complain of
vague, nondescript gastrointestinal discomfort,
including diarrhea and abdominal pain. These
patients may also develop nausea, dizziness,
headache, and weight loss. Intestinal obstruction
and vitamin B 12 –induced macrocytic anemia may
develop in persons infected with Diphyllobothrium
latum. Liver and lung involvement are
common in persons infected with E. granulosus.
These patients may develop a persistent cough,
localized pain, and eosinophilia. Under appropriate
conditions, a serious allergic response may
develop, known as anaphylactic shock, which
produces large amounts of histamine and other
chemical mediators and may be fatal.
Quick Quiz! 10-3
A persistent cough, localized pain, and liver and lung
involvement are associated with an infection with
which of the following cestodes? (Objective 10-6)
A. Diphyllobothrium latum
B. Echinococcus granulosus
C. Both A and B
D. Neither A nor B
CESTODE CLASSIFICATION
Members of the class Cestoda belong to the
phylum that also contains the flukes (Chapter
11) known as Platyhelminthes. The species discussed
in this chapter are listed in Figure 10-1
and may be divided into two categories, intestinal
and intestinal-extraintestinal.
Taenia saginata
(tee’nee-uh/sadj-i-nay’tuh)
Common name: Beef tapeworm.
Common associated disease and condition
names: Taeniasis, beef tapeworm infection.
Taenia solium
(tee’nee-uh/so-lee’um)
Common name: Pork tapeworm.
Common associated disease and condition
names: Taeniasis, pork tapeworm infection.
There are two members of the Taenia species
that are of clinical significance to humans, Taenia
solium and Taenia saginata. With only a few
notable exceptions (see later), the two organisms
are similar in most respects. Thus, these two
organisms will be discussed together.
Morphology
Eggs. The eggs of T. solium and T. saginata
are indistinguishable (Fig. 10-2; Table 10-1).
Ranging in size from 28 to 40 µm by 18 to 30
µm, the average, somewhat roundish Taenia spp.
egg measures 33 by 23 µm. The egg consists of
a hexacanth embryo, including the standard