[Elizabeth_Zeibig]_Clinical_Parasitology__A_Practi(z-lib.org)

CHAPTER 8 The Nematodes
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freshly passed stool may be unsegmented or
show a visible embryonic cleavage, usually at the
two-, four-, or eight-cell stage. A thin, smooth,
colorless shell provides protection for the developing
worm. Because the size ranges of these two
organisms are so close and the other characteristics
are identical, recovered eggs are considered
as indistinguishable and are usually reported as
hookworm eggs.
Rhabditiform Larvae. The average immature,
newly hatched hookworm rhabditiform larva
measures approximately 15 by 270 µm (Fig.
8-12; Table 8-9). The actively feeding larva will,
at a minimum, double in length, ranging from
540 to 700 µm, when it is only 5 days old. This
morphologic form is characterized by the presence
of a long oral cavity known as a buccal
cavity or buccal capsule and a small genital
TABLE 8-8
Parameter
Size
Length
Hookworm Egg: Typical
Characteristics at a Glance
Description
Necator, 60-75 µm;
Ancylostoma, 55-60 µm
Width 35-40 µm
Embryonic cleavage Two-, four-, or eight-cell stage
Shell
Smooth, colorless
TABLE 8-9
Hookworm rhabditiform
larva: Typical Characteristics
at a Glance
Parameter Description
Size
Newly hatched 270 by 15 µm
5 days old 540-700 µm long
Other features Long buccal cavity; small genital
primordium
Long buccal
cavity
Anus
Small genital
primordium
Esophagus
A
Average size of immature,
newly hatched rhabditiform larvae: 270 m by 15 m
Size range at 5 days old: 540-700 m long
B
C
FIGURE 8-12 A, Hookworm rhabditiform larva. B, Hookworm rhabditiform larva. Note long buccal capsule and lack
of prominent genital primordium. C, Hookworm rhabditiform, larval form buccal capsule. (B, C from Mahon CR,
Lehman DC, Manuselis G: Textbook of diagnostic microbiology, ed 4, St Louis, 2011, Saunders.)