Medicinal plants as potential therapeutic agents for trypanosomosis: a systematic review

Trypanosomiasis is a neglected tropical disease caused by various trypanosome species that affects both humans and livestock with catastrophic implications across the endemic areas. Plants have been used for many centuries to establish or bring back health, well-being, and as cure for several illnesses. We performed a systematic review using the PRISMA guidelines to compile the results of studies carried out in both in vitro and in vivo investigations, examined the effect of plant extracts on trypanosomosis treatment and risk of bias of the studies. Published articles were appraised and only those with the requisite inclusion criteria looking at the efficacy of different medicinal plant extracts used against trypanosomosis globally from 1990 to 2020 in ScienceDirect, PubMed, SpingerLink, Scopus and Web of Science were used for this systematic review. A total of 761 medicinal plant species were evaluated for antitypanosomal activity with Fabaceae and Euphorbiaceae families being frequently studied. After comparative analysis, two plant species, namely, Khaya senegalensis and Terminalia superba produced best antitrypanosomal activity both in vitro and in vivo. Leaves (74%) and stem barks (38%) were most used plant parts. Medicinal plant extracts demonstrated in vivo antirypanosomal efficacy either singularly or synergistically at dosages < 2000 mg/kg, that resulted in elimination of parasitaemia and reduction of trypanosomosis clinical symptoms. On the other hand, most of the extracts, had an in vitro antirypanosomal activity within minutes after application in a concentration-dependent manner. Bias analysis showed the lack of standardized experimental designs and failures in statistical tests. There is lack of studies for evaluation of efficacy of medicinal plant extracts against Trypanosoma equiperdum and T. vivax both in vitro and in vivo amongst pathogenic trypanosomes. Medicinal plant extracts have potential therapeutic activity against pathogenic trypanosomes infecting animals and humans as suggested by majority of in vitro studies but require verification of in vivo efficacy and toxicity studies which are lacking.