Answer to Case 65
This was a case of hookworm infection. Several respondents thought this
was a trematode infection (e.g., Clonorchis spp., Paragonimus
spp., etc.). Tangential sections are not as good as cross-sections
to illustrate body morphology. However, in this case, the buccal
capsule is clearly visible. Several features excluded trematodes: the presence of a cuticle rather than tegument on the
body surface; a distinct layer of muscle cells composing the body wall;
and, most distinctly, the presence of a body cavity (best seen in Figure
C). Trematodes have a solid body composed of a parenchymatous
matrix in which the internal organs are embedded. Muscle fibers
course through the parenchyma, but do not form a heavy band as part of
the body wall as in nematodes.
features observed were:
presence of a body cavity.
- a large
buccal capsule, clearly seen in Figures A and B.
- the size
of the worm, which was within the range for hookworms (5 to 11 mm).
- a thick
presence of a long and club-shaped esophagus, which was clearly visible in all three images.
in the host (small intestine).
worms are usually required to differentiate the two primary species of
hookworms infecting humans, Ancylostoma duodenale and Necator
americanus. Morphological features such as the spicules found
on male worms and presence of teeth or cutting plates (in male and female
worms) have to be used to make species identification. Due to
the volume of international travel, the geographic distribution of both
species has increased and become more overlapping, especially in southeast
Asia. Historically, Ancylostoma duodenale was more prevalent
in southern Europe, Sub-Saharan Africa, and Asia, whereas Necator
americanus was typically found in the western hemisphere as well as
southern Europe, southern Asia, India, Melanesia, and Polynesia.
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