Antiparasitic Activity
The extensive use of anthelmintics in livestock has led to the development of resis-
tance to one or more of the widely available anthelmintics in many countries [65].
5.14 Antiparasitic Activity 113
Parasite infestations caused by helminth species are prevalent in poor rural parts
of southern Africa. Internal parasites in humans and animals, particularly worm
infestations, are commonly treated with traditional remedies, and a wide variety of
plant species is employed for this purpose. As it is time-consuming and expensive
to verify the performance of extracts of these plants in vivo, we use in vitro models
as a preliminary screening technique.
Assaying plant extracts against the free-living nematode Caenorhabditis elegans
[66, 67] is much simpler, quicker, and cheaper than using parasitic nematodes,
which are often difficult to maintain in culture. Most of the commercially available
broad-spectrum anthelmintic drugs in popular use demonstrate activity against C.
elegans [66]. There are clearly limitations to extrapolating activity against a free-liv-
ing nematode to activity against parasitic nematodes [68]. In some broad screening
studies, it was found that a large proportion of plant extracts tested showed activity
against the free-living Caenorhabditis nematode [51, 69, 70], providing some ratio-
nale for the use of these plants in treating helminth infestations in both humans
and their livestock. Members of the Combretaceae featured in other anthelmintic
activity investigations, and leaf extracts of some members of the family revealed
noteworthy anthelmintic activity against C. elegans [24].
We also apply plant extracts to in vitro assays against parasitic nematode species.
Larval development and egg hatch assays against Haemonchus contortus and Trichostrongylus
colubriformis form the basis of these investigations. These two species
are among the most important nematodes causing disease in livestock in southern
Africa. The parasitic nematodes are cultured in monospecifically infected lambs,
and eggs of each species are collected from the feces when needed for assay. The
larval development assay [71] analyzes the ability of the test substance to retard the
development of eggs to infective larvae .The egg hatch assay [72] determines inhi-
bition of hatching of freshly collected nematode eggs and, when combined with the
larval development assay, supplies a reasonable indication of the anthelmintic ac-
tivity of plant extracts.
In a study in which the in vitro anthelmintic activity of 20 plants was tested
against the parasitic nematodes H. contortus and T. colubriformis, interesting re-
sults were obtained (JB Githiori, personal communication). The criteria of plant se-
lection included firstly the prior discovery of anthelmintic activity against the free-
living nematode Caenorhabditis elegans [24, 51]. A second criterion was the docu-
mentation of plant usage in ethnoveterinary medicine for the treatment of nema-
tode parasites of ruminant livestock [73]. Thirdly, the ethnoveterinary use of plants
by rural farmers (D Luseba, personal communication) was taken into account, and
lastly, information from available literature sources was incorporated. Aqueous
and acetone plant extracts were prepared and submitted to the egg hatch and larval
development assays described above. Most of the plants showed minimal effects
on egg hatching and larval development with the exception of Aloe species, and
these results are being prepared for publication. Another study tested the activity
of acetone extracts of the leaf, bark, and root of Peltophorum africanum, a plant tra-
ditionally used to treat helminthosis, against H. contortus. At a concentration of
0.2 mg mL–1, the extracts inhibited egg hatching and larval development, providing
114 5 Plant Extracts Used to Manage Bacterial, Fungal, and Parasitic Infections in Southern Africa
a degree of support for the traditional use of the plant, but this needs to be con-
firmed with further studies.
Research into correlations between lethal effects of plant extracts against parasit-
ic nematodes on the one hand and free-living nematodes on the other hand re-
mains an ongoing area of interest in our group.
The extensive use of anthelmintics in livestock has led to the development of resis-
tance to one or more of the widely available anthelmintics in many countries [65].
5.14 Antiparasitic Activity 113
Parasite infestations caused by helminth species are prevalent in poor rural parts
of southern Africa. Internal parasites in humans and animals, particularly worm
infestations, are commonly treated with traditional remedies, and a wide variety of
plant species is employed for this purpose. As it is time-consuming and expensive
to verify the performance of extracts of these plants in vivo, we use in vitro models
as a preliminary screening technique.
Assaying plant extracts against the free-living nematode Caenorhabditis elegans
[66, 67] is much simpler, quicker, and cheaper than using parasitic nematodes,
which are often difficult to maintain in culture. Most of the commercially available
broad-spectrum anthelmintic drugs in popular use demonstrate activity against C.
elegans [66]. There are clearly limitations to extrapolating activity against a free-liv-
ing nematode to activity against parasitic nematodes [68]. In some broad screening
studies, it was found that a large proportion of plant extracts tested showed activity
against the free-living Caenorhabditis nematode [51, 69, 70], providing some ratio-
nale for the use of these plants in treating helminth infestations in both humans
and their livestock. Members of the Combretaceae featured in other anthelmintic
activity investigations, and leaf extracts of some members of the family revealed
noteworthy anthelmintic activity against C. elegans [24].
We also apply plant extracts to in vitro assays against parasitic nematode species.
Larval development and egg hatch assays against Haemonchus contortus and Trichostrongylus
colubriformis form the basis of these investigations. These two species
are among the most important nematodes causing disease in livestock in southern
Africa. The parasitic nematodes are cultured in monospecifically infected lambs,
and eggs of each species are collected from the feces when needed for assay. The
larval development assay [71] analyzes the ability of the test substance to retard the
development of eggs to infective larvae .The egg hatch assay [72] determines inhi-
bition of hatching of freshly collected nematode eggs and, when combined with the
larval development assay, supplies a reasonable indication of the anthelmintic ac-
tivity of plant extracts.
In a study in which the in vitro anthelmintic activity of 20 plants was tested
against the parasitic nematodes H. contortus and T. colubriformis, interesting re-
sults were obtained (JB Githiori, personal communication). The criteria of plant se-
lection included firstly the prior discovery of anthelmintic activity against the free-
living nematode Caenorhabditis elegans [24, 51]. A second criterion was the docu-
mentation of plant usage in ethnoveterinary medicine for the treatment of nema-
tode parasites of ruminant livestock [73]. Thirdly, the ethnoveterinary use of plants
by rural farmers (D Luseba, personal communication) was taken into account, and
lastly, information from available literature sources was incorporated. Aqueous
and acetone plant extracts were prepared and submitted to the egg hatch and larval
development assays described above. Most of the plants showed minimal effects
on egg hatching and larval development with the exception of Aloe species, and
these results are being prepared for publication. Another study tested the activity
of acetone extracts of the leaf, bark, and root of Peltophorum africanum, a plant tra-
ditionally used to treat helminthosis, against H. contortus. At a concentration of
0.2 mg mL–1, the extracts inhibited egg hatching and larval development, providing
114 5 Plant Extracts Used to Manage Bacterial, Fungal, and Parasitic Infections in Southern Africa
a degree of support for the traditional use of the plant, but this needs to be con-
firmed with further studies.
Research into correlations between lethal effects of plant extracts against parasit-
ic nematodes on the one hand and free-living nematodes on the other hand re-
mains an ongoing area of interest in our group.
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