[Elizabeth_Zeibig]_Clinical_Parasitology__A_Practi(z-lib.org)

CHAPTER 9 The Filariae
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No sheath (found in tissue only)
Size range: 148-355 m long
FIGURE 9-7 Onchocerca volvulus microfilaria.
Treatment
Surgical removal of adult L. loa worms is the
treatment of choice. Extracting these worms
when they are attempting to cross the eye or the
bridge of the nose is the ideal time to remove
them. Unfortunately, it is impossible to select the
appropriate time to perform such a procedure in
advance.
The medication of choice for the treatment of
L. loa is diethylcarbamazine (DEC). Although
this antiparasitic drug is known to be effective,
it should be used with caution. Its use to treat
heavily infected patients may result in serious
side effects, including encephalitis.
Prevention and Control
Personal protection measures are essential to stop
the spread of L. loa infection. In addition, destroying
the vector breeding areas, although probably
not economically or logistically feasible, would
also help in halting the spread of infection. The
use of prophylactic DEC, particularly for nonnatives
visiting endemic areas, has also proven
effective.
Quick Quiz! 9-8
A small threadlike worm is observed under the conjunctiva
of the eye. What organism and form is most
likely? (Objective 9-8)
A. Wuchereria bancrofti adult
B. Brugia malayi microfilaria
C. Onchocera volvulus larva
D. Loa loa adult
FIGURE 9-8 Onchocerca volvulus microfilaria. Note the
absence of a sheath (Giemsa stain, ×400). (Courtesy of
WARD’S Natural Science Establishment, Rochester, NY.)
Quick Quiz! 9-9
What type of periodicity does Loa loa exhibit? (Objective
9-8)
A. Nocturnal
B. Subperiodic
C. Diurnal
D. None
Onchocerca volvulus
(onk’o-sur’kuh/vol’vew-lus)
Common name: Blinding filaria.
Common associated disease and condition
names: River blindness, onchocerciasis.
Morphology
Microfilariae. Onchocerca volvulus ranges in
length from 150 to 355 µm (Figs. 9-7 and 9-8;
Table 9-4). The one primary characteristic that
distinguishes this organism from the other