A review of Aloe species used in traditional medicine in East Africa

There is widespread use of Aloe species in traditional healing practices in East Africa for a variety of diseases. Unfortunately, there is a tendency of mistakenly referring to all species of the genus Aloe as Aloe vera, despite the diversity of aloes in the region. The names for the different Aloe species in local languages are usually the same for the different species. The aim of this review was to assess the medicinal uses of the indigenous little-known and other popular Aloe species in East Africa. Relevant articles, books, theses, dissertations, patents, and other English-only reports on the ethnobotany, traditional medicinal uses, pharmacological or biological activity, toxicity, phytochemistry, trade, conservation, etymology, and distribution of aloe species in East Africa (Uganda, Tanzania, Kenya, Rwanda, and Burundi) were reviewed. Databases such as PubMed, Web of Science, Scopus, Science Direct, and search engines such as Google Scholar, were searched between May and September 2020. Scientific names and synonyms of the aloe species were verified and resolved using Plants of the World Online (POWO, http://powo.science.kew.org/). Forty-nine of the over 180 Aloe species known in East Africa, are traditionally used for treating various ailments. Most of the Aloe species (85.7%) had direct references to their use in traditional medicine. Thirty-six species (73.5%) had some form of phytochemical analysis performed on them. Most of the Aloe species (67.3%) have never been investigated for any biological activity. The distinctive constituents in aloe leaves are phenolic compounds including chromone, anthraquinone or anthrone derivatives. Aloe aageodonta, A. ballyi, and A. christianii are known to be poisonous to humans when used in high doses, despite being used in traditional medicine. Aloe elgonica, A. ferox, and A. lateritia are all highly toxic to brine shrimp, whereas A. macrosiphon, A. vera, and A. volkensii cause a wide range of toxic side effects, such as bloody diarrhoea, dehydration, kidney damage, miscarriage, nausea and vomiting, hepatotoxicity, and acute renal failure, when used for long periods and in high doses. Several Aloe species are used in East Africa for treating various ailments. However, most of the local Aloe species have not been scientifically investigated for their biological activity, as well as their toxicity.