[Elizabeth_Zeibig]_Clinical_Parasitology__A_Practi(z-lib.org)

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CHAPTER 8 The Nematodes
Amorphous mass
of protoplasm
Heavy
albuminous
coating
40-75 m
Thin shell
A
Size range: 85-95 m by 38-45 m
B
FIGURE 8-6 A, Ascaris lumbricoides, unfertilized egg. B, Ascaris lumbricoides, decorticated unfertilized egg, ×400.
(Courtesy of WARD’S Natural Science Establishment, Rochester, NY.)
TABLE 8-5
Parameter
Size
Shape
Embryo
Shell
Other features
Ascaris lumbricoides
Unfertilized Egg: Typical
Characteristics at a Glance
Description
85-95 µm by 38-45 µm; size
variations possible
Varies
Unembryonated; amorphous mass
of protoplasm
Thin
Usually corticated
TABLE 8-7
Ascaris lumbricoides Adults:
Typical Characteristics at
a Glance
Characteristic Female Adult Male Adult
Size (length) 22-35 cm Up to 30 cm
Color
Creamy white
pink tint
Creamy white
pink tint
Other features Pencil lead
thickness
Prominent
incurved tail
TABLE 8-6
Ascaris lumbricoides
Fertilized Egg: Typical
Characteristics at a Glance
Parameter Description
Size 40-75 µm by 30-50 µm
Shape
Rounder than nonfertilized version
Embryo
Undeveloped unicellular embryo
Shell
Thick chitin
Other features May be corticated or decorticated
coating called a chitin, also known as a shell, is
sandwiched in between the embryo and mammillated
albuminous material (corticated). Both
layers protect the embryo from the outside environment.
Eggs lacking an outer mammillated,
albuminous coating (refered to as decorticated)
fertilized eggs (see Fig. 8-8) may also be present.
The chitin shell is less evident in corticated eggs
than in those that have lost their outer albuminous
coating.
Adults. Adult A. lumbricoides worms usually
assume a creamy white color with a tint of pink
Fine striations are visible on the cuticle (a surface
covering present on adult nematodes). Ascaris
adult worms are the largest known intestinal
nematodes (Table 8-7). The average adult male
(Fig. 8-9) is small, seldomly reaching 30 cm in
length. The male is characteristically slender and
possesses a prominent incurved tail. The adult
female (Fig. 8-10) measures 22 to 35 cm in length
and resembles a pencil lead in thickness.
Laboratory Diagnosis
The specimen of choice for the recovery of A.
lumbricoides eggs is stool. Adult worms may be
recovered in several specimen types, depending