Biomedical Engineering Reference
In-Depth Information
CH
3
CH
3
H
O
O
CH
3
H
3
C
O
O
O
O
R
H
H
3
C
O
H
3
C
CH
3
O
OH
O
HO
S
As
NH
2
HO
O
H
CH
3
S
NN
L
-Oleandrose
O
CH
3
H
N
NH
2
H
OH
21.1
R=-C
2
H
5
(80%) or -CH
3
(20%)
21.2
FIGURE 21.1
Ivermectin (
21.1
) is a mixture containing at least 80% of the analog in which R = C
2
H
5
, and
not more than 20% of the analog in which R = CH
3
. Coni guration of melarsopol (
21.2
).
of the parasites. This leads to death of microi lariae, the i rst larval stage. The drug does not cause
immediate death of the adult parasite but reduces the worm's life span.
21.3 INFECTIONS CAUSED BY PROTOZOAN PARASITES
OTHER THAN
PLASMODIUM
Protozoan parasites are single-celled organisms, which have an animal-like nutrition (they cannot
perform photosynthesis). The life cycle of protozoan parasites involves two hosts; the smaller of which
typically is named the vector. Important genera are
Plasmodium
,
Tr ypa nosom a
, and
Leishmania
.
21.3.1 T
RYPANOSOMIASIS
Two major tropical diseases, American trypanosomiasis (Chagas disease) and African trypanoso-
miasis (sleeping sickness) are caused by
T. cruzi
and subspecies of
T. brucei
, respectively. African
trypanosomiasis is spread with tsetse l ies (
Glossina
species). If untreated, the disease may be lethal
since the parasites enter the CNS causing coma (explaining the name sleeping disease) and death.
Approximately 48,000 persons are estimated to die from the disease each year. The only drug avail-
able for treatment of the disease in a late stage is the arsenical drug melarsoprol (
21.2
) (Figure 21.1),
developed more than 50 years ago. It is known to cause a range of side effects including convulsions,
fever, loss of consciousness, rashes, nausea, and vomiting. It is fatal in a signii cant fraction of cases.
Early stages of the disease are treated with pentamidin and suramin.
21.3.2 L
EISHMANIASIS
Leishmaniasis is caused by parasites of the genus
Leishmania
. The diseases vary from simple self-
healing skin ulcers (cutaneous leishmaniasis), severe disi guring of nose, throat, and mouth cavities
(mucocutaneous leishmaniasis) to life-threatening infections (visceral leishmaniasis). Visceral
leishmaniais can be fatal if untreated. Approximately 12 million humans are infected with leishma-
niasis and it is estimated that 59,000 die each year. The parasites nourish in the macrophages. The
life cycle is illustrated in Figure 21.2.
Until recently no orally active drug was known for leishmaniasis but the treatment was based on
amphotericin B (
21.3
) (Figure 21.3), pentamidine or antimony containing drugs like sodium stibo-
gluconate and meglumine antimonate. Liposomal formulations of amphotericin B have increased
the efi ciency of the drug. Application of a drug in vesicles as liposomes will target the drug
