[Elizabeth_Zeibig]_Clinical_Parasitology__A_Practi(z-lib.org)

CHAPTER 9 The Filariae
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Treatment
The drug of choice for the treatment of O. volvulus
microfilariae is ivermectin. There is no
known medication on the market that effectively
destroys both the adult worms and microfilariae
without some toxic effects or complications.
Therapy may be necessary for very long periods
of time due to the long life of the adult worms.
They can live for 15 years or more. When appropriate,
surgical removal of the adult worms from
an infected nodule may be performed to reduce
the number of microfilariae present in the subcutaneous
tissue.
Prevention and Control
Exercising personal protection when entering
endemic areas is crucial to halting the spread of
O. volvulus. In addition, controlling the vector
breeding grounds with the use of insecticides, as
well as areas in which the adult insects reside, is
also essential to eradicate the parasite but has
been proven to be very difficult.
Quick Quiz! 9-10
How do the microfilariae of Onchocerca volvulus
differ from those of other filarial? (Objective 9-13)
A. The presence of a sheath.
B. Nuclei are present continuous to the end of the
tail
C. They exhibit diurnal periodicity
D. They are found in the skin rather than blood
OTHER FILARIAL ORGANISMS
Other microfilarial parasites do exist. Although
primarily nonpathogenic, there are times when
treatment is indicated. Despite their varying
pathogenicity, these organism produce microfilariae
that must differentiated from others known
to be pathogenic. Two filarial parasites (Mansonella
ozzardi and Mansonella perstans) that fit
into this category are described in the sections
that follow.
Mansonella ozzardi
(man”so-nel’ah/o-zar’de)
Common name: New World filaria.
Common associated disease and condition
names: None (considered as a nonpathogen).
Morphology
Microfilariae. As with the other microfilariae,
the average Mansonella ozzardi microfilaria has
a rounded, blunt anterior end and measures
approximately 220 µm (Fig. 9-9; Table 9-5). The
posterior end is short and not as tapered as that
of Onchocerca. The organism contains numerous
nuclei that do not extend to the tip of the
long, narrow and tapered tail. There is no sheath
present. It is similar in appearance to that of O.
volvulus but is found in blood rather than skin
snips. The microfilariae do not exhibit any periodicity
in the blood.
Adults. The typical adult female M. ozzardi
may range in length from 65 to 80 mm, with an
Quick Quiz! 9-11
Skin snips are the specimen of choice for diagnosis of
infection with: (Objective 9-8)
A. Loa loa
B. Onchocerca volvulus
C. Brugia malayi
D. Wuchereria bancrofti
TABLE 9-5
Parameter
Size range
Sheath
Arrangement of nuclei in
tail
Mansonella ozzardi
Microfilaria: Typical
Characteristics at a Glance
Description
220 µm in length
Absent
Numerous; do not
extend to tip of tail