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CHAPTER 11 The Trematodes
Large lateral spine
Developed
miracidium
A
Size range: 112-182 m by 40-75 m
B
FIGURE 11-9 A, Schistosoma mansoni egg. B, Schistosoma mansoni egg. (B from Mahon CR, Lehman DC,
Manuselis G: Textbook of diagnostic microbiology, ed 4, St Louis, 2011, Saunders.)
TABLE 11-5
Schistosoma Species Eggs:
Typical Characteristics at
a Glance
S. mansoni S. japonicum S. haematobium
Size Range
112-182 µm by
40-75 µm
Shape
Oblong
Egg Contents
Developed
miracidium
50-85 µm by
38-60 µm
Somewhat
roundish
Developed
miracidium
110-170 µm by
38-70 µm
Somewhat oblong
Developed
miracidium
Appearance and Location of Spine
Large; lateral Small; lateral* Large; terminal
*Difficult to see.
70 µm. The presence of a large, prominent, terminal
spine distinguishes the egg from that of
other Schistosoma spp.
Adults. As noted, the adults of Schistosoma
are the only trematodes discussed in this chapter
that have separate sexes. Unlike the other
adult trematodes discussed thus far, the schistosomes
are rounder in appearance. Although the
typical female measures 2 cm in length and
the male measures 1.5 cm, the male surrounds
the female almost completely, facilitating copulation
(Fig. 11-12).
Laboratory Diagnosis
Laboratory diagnosis of S. mansoni and S. japonicum
is accomplished by recovery of the eggs in
stool or rectal biopsy specimens. The specimen
of choice for the recovery of S. haematobium
eggs is a concentrated urine specimen. In addition,
a number of immunodiagnostic techniques,
including ELISA, are also available.
Life Cycle Notes
Human infection with Schistosoma occurs in
fresh water following the penetration of forktailed
cercariae into the skin. The resulting schistosomule
migrates into the bloodstream, where
maturation into adulthood is completed. The
location of the adult flukes varies by species. S.
mansoni and S. japonicum reside in the veins that
surround the intestinal tract, as well as in the
blood passages of the liver. S. haematobium
resides in the veins surrounding the bladder.
Females lay thousands of eggs daily, which make
their way from the bloodstream through the
tissue into the colon (S. mansoni and S. japonicum)
or the urine (S. haematobium). The eggs
produce enzymes that help them travel through
the tissue to be excreted. Once an egg reaches
fresh water, the miracidium is released from the
egg and must locate a snail, where it develops
into the cercariae.