Medicinal plants as a source of antiparasitics: an overview of experimental studies

Figures & data

Table 1. Traditional uses of medicinal plants to treat veterinary ailments.

Plant scientific name (Common name)	Family	Parts used	Disease target	Country
Azadirachta indica (Neem)	Meliaceae	Leaves	Indigestion, tick infestation and toxaemia	India, Pakistan
Acokanthera oppositifolia (Bushman’s poison)	Apocynaceae.	Leaves	Gastrointestinal and external parasites	Africa
Allium cepa (Onion)	Amaryllidaceae	Cloves	Gastrointestinal parasites, foot and mouth disease, poisoning	India
Allium sativum (Garlic)	Amaryllidaceae	Cloves	Gastrointestinal parasites	India
Cannabis sativa (Hemp)	Cannabaceae	Resin	Abdominal pain	India
Datura metel (Thornapple)	Solanaceae	Fresh fruits	Gastrointestinal parasites	China
Mentha spicata (Common mint)	Lamiaceae	Whole plant	Gastrointestinal parasites
Musa paradisiaca (Banana)	Musaceae	Leaves	Gastrointestinal parasites	Pakistan
Nicotiana tabacum (Tobacco)	Solanaceae	Leaves	Ectoparasites
Piper nigrum (Black pepper)	Piperaceae	Seeds	Indigestion, diarrhea, flatulence, and poisoning	India
Senna italica (Italian senna)	Fabaceae	Whole plant	Gastrointestinal parasites	Africa
Trachyspermum ammi (Ajwain)	Apiaceae	Seeds	Bloat	India
Trianthema portulacastrum (Black pigweed)	Aizoaceae	Whole plant	Gastrointestinal parasites	Pakistan
Vernonia anthelmintica (Purple fleabane)	Asteraceae	Seeds	Gastrointestinal parasites	India

Table 2. Plants and their compounds that have led to synthetic medicines.

Botanical source (common name)	Family	Lead compound	Chemical class	Disease target
Artemisia annua (sweet wormwood)	Asteraceae	Artemisinin	Alkaloids	Malaria
Atropa belladonna (belladonna)	Solanaceae	Atropine	Alkaloids	Bradycardia (low heart rate), pesticide poisoning
Catharanthus roseus (rose periwinkle)	Apocynaceae	Vinblastine, Vincristine	Alkaloids	Cancer
Cephaelis ipecacuanha (ipecac)	Rubiaceae	Emetine	Alkaloids	Amoebiasis
Cinchona ledgeriana (cinchona)	Rubiaceae	Quinine	Alkaloids	Malaria
Coffea arabica (Arabian coffee)	Rubiaceae	Caffeine	Alkaloids	Fatigue, drowsiness, and migraine
Colchicum autumnale (autumn crocus)	Colchicaceae	Colchicine	Alkaloids	Gout
Digitalis purpurea (common foxglove)	Plantaginaceae	Digoxin	Phytosterols	Heart failure and cardiac arrhythmias (abnormal heart rhythms)
Ginkgo biloba (ginkgo)	Ginkgoaceae	Ginkgolides	Terpenoids	Ischemic strokes
Justicia adhatoda (Malabar nut)	Acanthaceae	Vasicine	Alkaloids	Bronchitis and cough
Mucuna pruriens (monkey tamarind)	Fabaceae	Levodopa	Amino acid	Parkinsonism
Papaver somniferum (opium poppy)	Papaveraceae	Codeine, morphine	Alkaloids	Moderate to severe pain
Prunus africana (African cherry)	Rosaceae	Sitosterol	Phytosterols	Benign prostate hyperplasia
Salix spp. (willows)	Salicaceae	Aspirin	Alkaloids	Clot-related strokes and cardiovascular disease

Table 3. In vitro and in vivo measures for the efficacy of plant compounds against parasites.

Outcome measure	Definition
IC50 (Half maximal inhibitory concentration) *	The concentration of drug required for 50% inhibition of the treated population
LC50 (Median lethal concentration) *	The concentration of a drug that will lead to the deaths of 50% of the dosed population
EC50 (Median effective concentration) *	The concentration of a drug or toxicant which induces a response halfway between the baseline and maximum response
LC90 (Maximum lethal concentration) *	The concentration of a drug required to kill 90% of the parasite population
TC50 (Median toxic concentration) *	The concentration of a drug which induces 50% cell mortality
ED50 (Median effective dose) **	Dosage of a drug that produces a therapeutic effect in 50% of subjects
LD50 (Median lethal dose) **	Dosage of a drug required to kill 50% of the parasite population
LD90 (Maximum lethal dose) **	Dosage of a drug required to kill 90% of the parasite population

*In vitro.

**In vivo.

Table 4. In vitro screening studies of essential oils against gastrointestinal parasites.

Source of the essential oil	Family	Parasite tested	Outcome of the Study	Reference
Cymbopogon martinii (palm rose)	Poaceae	Haemonchus contortus	EHA LC50 = 0.13 mg/mL^2 LDA LC50 = 0.15 mg/mL^2	[167]
Cymbopogon martinii (palm rose)	Poaceae	Caenorhabditis elegans	ED50 = 125.4 µg/mL^2	[168]
Cymbopogon schoenanthus (camel grass)	Poaceae	Haemonchus contortus	EHA LC50 = 0.045 mg/mL^2 LDA LC50 = 0.063 mg/mL^2	[167]
Mentha piperita (mint)	Lamiaceae	Haemonchus contortus	EHA LC50 = 0.26 mg/mL^1 LDA LC50 = 0.26 mg/mL^1	[167]
Piper betle (betel pepper)	Piperaceae	Taenia solium	Time taken for Paralysis at 0.4% = 11 min^2 Time taken for Death at 0.4% = 19 min^2	[169]
Piper betle (betel pepper)	Piperaceae	Bunostomum trigonocephalum	Time taken for Paralysis at 0.4% = 13 min^2 Time taken for Death at 0.4% = 29 min^2	[169]
Syzygium aromaticum (clove)	Myrtaceae	Giardia duodenalis	IC50 = 134 µg/mL^3	[170]
Thymus vulgaris (thyme)	Lamiaceae	Haemonchus contortus	EHA IC50 = 0.436 mg/mL^2 LDA IC50 = 0.0131 mg/mL^2	[112]
Thymus vulgaris (thyme)	Lamiaceae	Entamoeba histolytica	MIC after 24 h = 0.7 mg/mL^3	[171]

1= No significant effect; 2 = significant reduction in parasite survival compared to controls; 3 = significant reduction in parasite population growth compared to controls.

EHA= Egg hatch assay; LDA= Larval development assay; MIC= Minimal inhibitory concentration.

Table 5. In vitro screening studies of plant-derived compounds against gastrointestinal parasites.

Compound	Chemical group	Source of the compound (Common name)	Family	Parasite tested	Outcome of the study	Reference
Hydrolysable tannins	Polyphenols	Acer rubrum (Canadian maple)	Sapindaceae	Caenorhabditis elegans	LC50 = 1.03 mg/mL^2	[172]
Hydrolysable tannins	Polyphenols	Quercus alba (white oak)	Fabaceae		LC50 = 0.75 mg/mL^2
Hydrolysable tannins	Polyphenols	Rosa multiflora (multiflora rose)	Rosaceae		LC50 = 2.14 mg/mL^2
Allyl alcohol	Polyphenols	Allium sativum (garlic)	Amaryllidaceae	Giardia duodenalis	IC50 = 7 µg/mL^3	[149]
Allyl mercaptan	Organosulfur	Allium sativum (garlic)	Amaryllidaceae	Giardia duodenalis	IC50 = 37 µg/mL^3	[149]
Bromelain	Polyphenols	Ananas comosus (pineapple)	Bromeliaceae	Haemonchus contortus	LC50 = 0.50 mg/mL^3	[173]
Gallic acid	Polyphenols	Anogeissus leiocarpus (African birch)	Combretaceae	Caenorhabditis elegans	LC50 = 3.22 mM^2	[113]
Gentisic acid	Polyphenols				LC50 = 6.12 mM^1
Ellagic acid	Polyphenols				LC50 = 0.085 mM^2
Deoxysappanone B 7,4	Polyphenols	Biancaea sappan (sappan wood)	Fabaceae	Cryptosporidium parvum	EC50 = 0.734 µM^1 TC50 = 64.9 µM^1	[174]
Geraniol	Terpenoids	Cymbopogon martinii (palm rose)	Poaceae	Caenorhabditis elegans	ED50 = 66.7 µg/mL^2	[168]
(–)-Epicatechin	Polyphenols	Geranium mexicanum (geranium)	Geraniaceae	Entamoeba histolytica	IC50 = 1.9 µg/mL^3	[111]
				Giardia duodenalis	IC50 = 1.6 µg/mL^3
(+)-Catechin	Catechin	Geranium mexicanum (geranium)	Geraniaceae	Entamoeba histolytica	IC50 = 65.6 µg/mL	[111]
				Giardia duodenalis	IC50 = 33.9 µg/mL^1
Plumbagin	Polyphenols	Plumbago Spp.	Plumbaginaceae	Caenorhabditis elegans	LC50 = 220 µM for L4; 156 µM for L1^2	[175]
Condensed tannins	Polyphenols	Robinia pseudoacacia (false acacia)	Fabaceae	Caenorhabditis elegans	LC50 = 0.65 mg/mL^2	[172]
Seed alkaloids	Alkaloids	Sophora moorcroftiana (pea-flowered tree)	Fabaceae	Caenorhabditis elegans	LC50 = 14.29 mg/mL^2	[176]
Eugenol	Polyphenols	Syzygium aromaticum (clove)	Myrtaceae	Giardia duodenalis	IC50 = 101 µg/mL^3	[170]
Thymol	Polyphenols	Thymus vulgaris (thyme)	Lamiaceae	Haemonchus contortus	IC50 = 0.442 mg/mL^2	[112]
Cedrelone	Terpenoids	Toona ciliata (red cedar)	Meliaceae	Cryptosporidium parvum	EC50 = 0.267 µM^3	[174]
Asarini	Polyphenols	Zanthoxylum liebmannianum (prickly ash)	Rutaceae	Entamoeba histolytica	IC50 = 19.86 µg/mL^3	[177]
				Giardia duodenalis	IC50 = 35.45 µg/mL^3

1= no significant effect; 2 = significant parasite killing effect compared to controls; 3 = significant reduction in parasite population growth compared to controls.

Figure 1. Schematic representation of the mechanism of action and different pharmacological targets of plant extracts/compounds.

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