Plant extracts to control ticks of veterinary and medical importance: A review

• Ticks and diseases caused by ticks have an enormous impact on animal production in Africa.
• There is a growing resistance of ticks to commercially used acaricides.
• Traditional healers use plants to combat tick infestations in many developing countries.
• We evaluate the published efficacy of 66 plants species used to protect animals against ticks.

Farmers in developing countries are faced with many diseases that limit the productivity of their animals, many of these are caused by tick infestations. Years of use and overuse of available chemical ectoparasiticides have resulted in the large scale development of resistance in these parasites as well as negative environmental impacts. To reduce these impacts, much focus has been placed on the search for alternative, environmentally friendly parasite control strategies with lower chance of the development of resistance. Many rural farmers have used plants to control ticks. In some cases the traditional use has been confirmed, in other cases, only the traditional use has been documented. A review of published scientific articles was conducted for medicinal plants with in vitro acaricidal or tick-repellent activities against immature and adult stages of ticks. Veterinary databases (All Databases, CAB Abstracts and Global Health, Medline, Pubmed, Web of Science, BIOSIS Citation Index, Science Direct, Current Content Connect and Google Scholar) were used. The search words included “acaricidal”, “tick-repellent”, “medicinal plants”, “phytomedicine” and “anti-tick assays”. More than 200 plant species from several countries globally have tick-repellent or acaricidal properties using in vitro assays. The different extractions and plant parts used as well as the efficacy where available is listed. Species including Azadirachta indica, Gynandropsis gynandra, Lavendula augustifolia, Pelargonium roseum and Cymbopogon spp. had good acaricidal and larvicidal effects with 90–100% efficacy, comparable to those of currently used acaricides. A number of active compounds such as azadirachtin, carvacrol, linalool, geraniol and citronellal have been isolated. Based on their wide use by rural livestock farmers, plant-based compounds may be a good source of effective acaricidal preparations either as an extract or as a source of new acaricidal compounds. The focus may have to be on acaricidal rather than on repellent activities to facilitate control of ticks.