[Elizabeth_Zeibig]_Clinical_Parasitology__A_Practi(z-lib.org)

CHAPTER 9 The Filariae
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Phylum
Nemathelminthes
Class
Nematoda
Blood and Tissue Species
Wuchereria bancrofti
Brugia malayi
Loa loa
Onchocerca volvulus
Mansonella ozzardi
Mansonella perstans
FIGURE 9-1 Parasite classification: The filariae.
Sheath
Tail pointed, free from nuclei
Size range: 240-300 m long
FIGURE 9-2 Wuchereria bancrofti microfilaria.
and enlargement of skin and subcutaneous tissue
known as elephantiasis, to Calabar swellings
(transient swelling of subcutaneous tissues), eye
involvement, and even blindness.
Quick Quiz! 9-3
Which of the following is similar for all microfilariae
discussed? (Objective 9-13)
A. Presence of a sheath
B. Ability to exhibit periodicity
C. Location of the adult worms
D. The basic life cycle
FILARIAE CLASSIFICATION
The filariae belong to the same phylum and class
as the nematodes introduced in Chapter 8,
Nemathelminthes and Nematoda, respectively.
All six of the organisms discussed in this chapter
are blood and tissue species, listed in Figure 9-1.
Wuchereria bancrofti
(wooch-ur-eer’ee-uh/ban-krof’tye)
Common name: Bancroft’s filaria.
Common associated disease and condition
names: Bancroft’s filariasis or elephantiasis.
FIGURE 9-3 Wuchereria bancrofti microfilaria. Note the
presence of a sheath and absence of nuclei in the tip of
the tail (Giemsa stain, ×400). (Courtesy of WARD’S Natural
Science Establishment, Rochester, NY.)
Morphology
Microfilariae. The average microfilaria measures
240 to 300 µm in length (Figs. 9-2 and 9-3;
Table 9-1). A thin and delicate sheath surrounds
the organism. Numerous nuclei are contained
in the body. The cephalic or anterior end is blunt
and round. The posterior or tail end culminates
in a point that is free of nuclei. This is a key