[Elizabeth_Zeibig]_Clinical_Parasitology__A_Practi(z-lib.org)

204
CHAPTER 8 The Nematodes
Short esophagus
Cutting plates
Pointed tail
FIGURE 8-13 Hookworm filariform larva.
FIGURE 8-14 Necator americanus, buccal capsule.
TABLE 8-10
Parameter
Length of esophagus
Tail
Hookworm Filariform
Larva: Typical
Characteristics at a Glance
Description
Short
Pointed
primordium (i.e., a precursor structure to a
reproductive system consisting of a clump of cells
in an ovoid formation).
Filariform Larvae. The infective, nonfeeding
filariform larva emerges after the rhabditiform
larva completes its second molt (Fig. 8-13; Table
8-10). There are two notable characteristics that
aid in identifying this morphologic form. First,
this slender larva has a shorter esophagus than
that of Strongyloides stercoralis, a similar intestinal
nematode (covered later in this chapter).
Secondly, the hookworm filariform larva has a
distinct pointed tail.
Adults. Rarely seen, the small adult hookworms
appear grayish-white to pink in color,
with a somewhat thick cuticle (Figs. 8-14 to
8-17; Table 8-11). The anterior end typically
forms a conspicuous bend, referred to as a
hook—hence, the name hookworm. The hook is
usually much more pronounced in the N. americanus
adult than in that of A. duodenale and may
serve as a means of distinguishing among the two
species by the trained eye.
The average adult female hookworm usually
measures about 9 to 12 mm in length by 0.25 to
Size range: 9-12 mm long by 0.25-0.5 mm wide
FIGURE 8-15 Necator americanus, adult male.
Teeth
FIGURE 8-16 Ancylostoma duodenale, buccal capsule.
Copulatory
bursa
Size range: 5-10 mm long by 0.2-0.4 mm wide
FIGURE 8-17 Ancylostoma duodenale, adult female.