[Elizabeth_Zeibig]_Clinical_Parasitology__A_Practi(z-lib.org)

254
CHAPTER 10 The Cestodes
Terminal knob
(abopercular knob)
Operculum
A
Coracidium
(undeveloped embryo)
Size range: 55-75 m by 40-55 m
Average size: 65 m by 48 m
FIGURE 10-14 A, Diphyllobothrium latum egg. B, Diphyllobothrium latum egg, 400×. (B from Mahon CR, Lehman DC,
Manuselis G: Textbook of diagnostic microbiology, ed 4, St Louis, 2011, Saunders.)
B
TABLE 10-9
Parameter
Size range
Shape
Embryo
Shell
Other features
Diphyllobothrium latum
Egg: Typical Characteristics
at a Glance
Description
55-75 µm long, 40-55 µm wide
Somewhat oblong
Undeveloped, termed coracidium
Smooth; yellow-brown in color
Operculum on one end; terminal
knob on opposite end
Two long sucking grooves
FIGURE 10-15 Diphyllobothrium latum scolex.
Morphology
Eggs. The eggs of Diphyllobothrium latum
differ from the cestodes discussed thus far in that
they are not comprised of the typical hexacanth
embryo (Fig. 10-14; Table 10-9). Rather, the
average D. latum egg consists of a ciliated larval
stage known as a coracidium, surrounded by a
smooth yellow to brown shell. The egg is somewhat
oblong in shape. The typical size is from
55 to 75 µm by 40 to 55 µm, with an average of
65 by 48 µm. A lid structure, referred to as an
operculum, consumes one end of the egg. A small
but distinct terminal knob, also known as an
abopercular knob, extends from the opposite end
of the egg.
Scolices. The scolex of D. latum also varies
from the four cuplike suckers present on the
other cestode species discussed thus far (Fig.
10-15; Table 10-10). The D. latum scolex is
almond-shaped and contains two long, prominent,
sucking grooves.
Proglottids. D. latum proglottids are wider
than they are long (Fig. 10-16; Table 10-10).
Gravid proglottids characteristically contain a
centrally located uterine structure that frequently
assumes a rosette formation.
Laboratory Diagnosis
Diagnosis of D. latum is accomplished by examining
stool specimens for the presence of the
characteristic eggs and/or, less frequently, the
proglottids. On occasion, a scolex may also be