Introduction

The Kagera Region in northwestern Tanzania has a rich culture of traditional medicine practice which has the potential to improve the socio-economic development of the region, especially if the plants being used are evaluated for safety and efficacy. The recovery of knowledge and practices associated with medicinal plants is part of an important strategy that is now being linked to the conservation of biodiversity, the discovery of new medicines, and the bettering of the quality of life of poor rural communities [1].

Whereas there exists a big wealth of medicinal plants in the Kagera region very little has been achieved in their documentation and evaluation for biological activity. Among the few documentation studies done is the study by Chhabra and Mahunnah in 1994 [2], which for the first time documented some of the plants used in this region. The current study is the sixth of a recently renewed initiative to document [3, 4], evaluate for biological activity [5–7], and assess how plant genetic resources in the Kagera region can be utilized for the development of an herbal medicines industry and therefore contribute to efforts to reduce poverty. Another study done in the region not too long ago was on the documentation of plants used for the management of HIV and AIDS in Bukoba rural district, in which 75 plants belonging to 66 genera and 41 families were documented [8]. The most recent study reported on the plants used for causing abortion in which proof of the concept was established for 11 out of the 21 plants (52.4%) that were documented [9]. This last study provides strong evidence supporting the strength and authenticity of traditional medicine practice in the Kagera region.

The present study is an ethnomedical documentation of medicinal plants used in Kikuku village, Muleba district, north western Tanzania.

Methodology

Description of the study site

Muleba District lies to the south west of Bukoba town at 1° 50' 23" South, 31° 39' 16" East (Figure 1). It is a second-order administrative division in Tanzania with an average elevation of 1,363 meter above sea level. The area is mildly densely populated with 166 people per sq Km and has a humid ( > 0.65 p/pet) climate. It has a good reserve of medicinal plants as the land area is not cultivated and therefore most of the natural vegetation is still intact. The landscape is mostly covered with closed broad-leaved deciduous forest. It has a tropical savanna climate with a subtropical moist forest biozone. September is on average the month with most sunshine and there is no distinct peak month for rainfall.

Figure 1
figure 1

A map showing the research site at Muleba situated in the northwest part of Tanzania.

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The Ethnobotanical visit and documentation of plant information

Before starting the ethnobotanical visit to Kagera region, one of the research team members travelled to Bukoba to make prior arrangements with the Regional Cultural Office to identify prominent traditional healers in different parts of the region who would be interviewed during our visit. The advance arrangements were done for one week in which period preparations with select traditional healers were made ready for the documentation work. In Muleba District, one informant, a traditional healer practicing at Kikuku village was identified. The Regional Cultural Officers assisted in obtaining prior informed consent from the healer and thus helped to create trust and ease the interview process that subsequently followed. The visit to Kikuku was made on 27th and 28th February and 2nd March, 2008. A semi-structured questionnaire [10] was used to collect information about the plants in an herbal garden within the healer's banana farm, around his house, and in bushes bordering and far away from the farm. Information collected included the common/local names of the plants, parts used, the diseases treated, and methods of preparation, dosage, frequency and duration of treatments. Voucher specimens were made for all plants collected which were subsequently identified by Mr. Selemani Haji of the Department of Botany, University of Dar es Salaam. Duplicate vouchers are kept at the Herbaria of the Botany Department, University of Dar es Salaam and the Institute of Traditional Medicine, Muhimbili University of Health and Allied Sciences.

Literature survey to establish proof of claims

Literature information was retrieved from the NAPRALERT data base at the School of Pharmacy, University of Illinois at Chicago, and published journal papers were accessed through google, googlescholar and Pubmed. The strength and validity of information obtained from the informant was evaluated based on there being found similar ethnomedical claims in the literature or evidence of laboratory results that support the claims.

Results

Medicinal Plant diversity

A total of 49 plant species belonging to 47 genera and 24 plant families were documented (Table 1). The families Euphorbiaceae and Asteraceae with 6 plant species each (24.4%) had the highest representation followed by Fabaceae and Solanaceae (5 plants each, 20.4%). The family Lamiaceae had 3 plant species (6.1%), while Acanthaceae, Amaranthaceae, Apocynaceae, Asparagaceae and Curcubitaceae had two plant species each. The remaining 14 families were each represented by 1 species. The main life forms of the plants used were herbs (38.8%), shrubs (36.7%), trees (16.3%), and climbers (8.2%).

Table 1 Medicinal plant families in the study area with the corresponding number of genera and species
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The plant parts used for making herbal preparations included roots, leaves, stem barks, root barks, pods, tubers, sap, fruits and other aerial parts. The leaves were the most frequently used part (31 species; 63.3%) followed by the roots and aerial parts (each 7 species; 14.3%), fruits (4 species, 8.1%), stem barks (3 species; 6.1%), tubers (2 species; 4.0%).

Diseases treated

A wide variety of disease conditions are treated using remedies made from medicinal plants. The diseases for which many different species are used include skin conditions (10 species; 20%), bacterial infections and wounds (14 species; 28.6%), malaria (14 species; 28.6%), and gastrointestinal problems (11 species; 22.4%). Others are gynaecological problems including infertility (8 species; 16.3%), hypertension (5 species; 10.2%), viral infections (7 species; 14.3%), chest problems (5 species; 10.2%), diabetes (3 species; 6.1%), and cancer (2 species; 4.1%). Inflammatory conditions (arthritis, rheumatism), HIV and AIDS, and hernia are each treated using one species (6.1%).

In most cases two or more diseases are treated using one plant. The plant that showed the greatest versatility is Dracaena steudneri which is used to treat six different indications. Fourteen species are used to treat one disease condition each (Table 2).

Table 2 The medicinal plants of Kikuku village, Muleba District, Kagera Region
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Methods used in the preparation of herbal medicines

Medicines used were prepared mainly by boiling to make decoctions (40.5%), pounding to paste (14.49%), squeezing (8.69%), chewing (8.69%), soaking in water to make infusions (8.69%), burning to ash (7.24%), grinding to powder (7.24%) and baking under hot ashes (5.79%). Some of the methods were used in combination e.g. grinding bark and then boiling to make a decoction, burning leaves and then mixing with margarine to form paste amongst others (see Table 2 for other examples). The making of decoctions was carried out mostly by boiling the plant parts in water. In three cases they were prepared by making concoctions i.e. boiling more than one plant. In the treatment of yellow fever a concoction is made from the leaves of Trema orientalis which are pounded and boiled with the leaves of Combretum collinum and Erythrina abyssinica. Similarly, a concoction for the treatment of malaria and febrile convulsions is made by boiling the leaves of Sesbania macrophylla with the leaves of Orthosiphon suffrutescens and Solanum aculeastrum. In a third example the leaves of Orthosiphon thymiflorus are mixed with those of Solanum aculeastrum and boiled; or the leaves of Solanum aculeastrum are boiled with Orthosiphon suffrutescens and Sesbania sesban for the treatment of malaria and febrile convulsions. In the case of Amaranthus spinosus, milk instead of water, is used.

Efficacy of herbal remedies used in traditional medicine

Among the 49 plants used in Kikuku as herbal medicines, 25 (51.0%) were found to have similar ethnomedical claims or have been phytochemically or pharmacologically proven to be active in literature. Those with proven phytochemical or pharmacological activity included plants used for the treatment of malaria e.g. Bridelia micrantha [28, 29], Senna occidentalis [41, 42], and Clerodendrum myricoides [52, 53]. Other reports from the literature are the disinfectant and anti-inflammatory activity of Crinum papillosum [12], and hypotensive effect of Catharanthus roseus extracts in rats [13]. Rauvolfia vomitoria has been confirmed to have a strong antiplasmodial activity [14], while Melanthera scandens leaf extract inhibited indomethacin, ethanol and histamine induced ulcers [19] in confirmation of the traditional medicine uses. The use of Microglossa pyrifolia for the treatment of headaches and colds has been reported by another source [20], while for Canarium schweinfurthii the antimicrobial activity has been confirmed by laboratory results [21]. The use of Trema orientalis for treatment of viral infections has been reported elsewhere [24], while the anti-inflammatory activity of Cleome gynandra is supported by anti-inflammatory activity of a methanol extract of the leaves against adjuvant-induced arthritis in rats [25]. Other proven claims are the hepatoprotective effect of Cajanus cajan ethanol extract in rats [40] and the antimalarial activity of Abrus precatorius [39] and Clerodendrum myricoides [52, 53]. Orthosiphon suffrutescens does not yet has proof of the concept laboratory results, but it is used in Rwanda for the treatment of malaria [45]. Evidence from the literature supports the use of Amaranthus spinosus [11], Senna occidentalis [43], and Ageratum conyzoides [15–17] for the treatment of peptic ulcers or as antispasmodics. Other ethnomedical claims supported by the literature include plants used in the treatment of bacterial infections; including Dichrocephala integrifolia [18], Jatropha curcas [35–38] and Bridelia micrantha [29]. The use of Flueggea virosa for the treatment of skin conditions is well supported by its confirmed antifungal activity [47, 48]. Other plants in this study with ethnomedical claims supported by literature-based evidence are Canna indica [22, 23], Capsicum frutescens [49], Euphorbia hirta [30–34], Harungana madagascariensis [2, 44], Hibiscus fuscus [46], Solanum nigrum [50, 51], and Zehneria scabra [26, 27].

Discussion

Many of the plants used in Kikuku ethnomedicine belong to the families Euphorbiaceae and Asteraceae. The Euphorbiaceae comprises 317 genera and about 8,000 species [54, 55], making it one of the largest plant families. It consists of some very useful medicinal plants, such as Euphorbia Kansu [55], which probably explains their prominence in the ethnomedicine of the Kikuku people. Since time immemorial many Euphorbiaceae have been popular as medicinal plants [55] and their recorded presence in this study just goes further to buttress this fact. The diverse medicinal properties of the Euphorbiaceae are thought to be associated with its wide range of habitats which predispose plants in this family to high mutation loads (accruing from stressful habitats) and a large range of environmental stimuli making them to develop a wide array of defensive secondary metabolites [55]. Of the approximately 250,000 species of known flowering plants, nearly one in ten are members of the Asteraceae, a diverse family found in almost every habitat on all continents except Antarctica [56]. This fact could probably then explain the prevalence of the Asteraceae, alongside the Euphorbiaceae, in the ethnomedicine of the Kikuku people.

The finding in this study that herbs and shrubs are the predominant life-forms used as medicines is consistent with other reported studies [57, 58]. The popularity of herbs as a source of herbal therapies is often attributed to their high pharmacologically active components compared to woody plant forms [59] whilst shrubs seem to be preferred due to the fact that their availability all year round as they are relatively drought resistant and are not affected by seasonal variations [60]. Some of the plants reported in this study (e.g. Ageratum conyzoides, Amaranthus spinosus, Bridelia micrantha, Capsicum frutescens, Clerodendrum myricoides, Draceana steudneri, Dicrocephalus integrifolia, Euphorbia hirta, Ricinus communis, Senna occidentalis, and Zehneria scabra) have, variously, been found to have similar or different ethno-medicinal uses elsewhere [57, 60–65]. This can be considered to be a reliable indication of their pharmacological effectiveness having been tested in different areas by different cultures [60].

This study shows that leaves, followed by roots and other aerial parts are preferred in the preparation of treatment recipes. It is tempting to speculate that practitioners of traditional medicine in Kikuku are conservation conscious and thus mainly use leaves so that they can sustain their supply of this herbal resource. However, on the converse, use of leaves could also be a severe threat to some rare and slowly reproducing medicinal plants [66]. Although the idea that herbalists in Kikuku are aware of the importance of conservation is demonstrated in the widespread establishment of home gardens, it would still be premature to arrive at such a conclusion. More studies have to be done to confirm this assertion. Nevertheless, the use of leaves as a preferred source of traditional medicines has also been reported elsewhere [67]. Their preference to other plant parts is commonly thought to be due to their accumulation of active principles like inulins, tannins and other alkaloids [68].

A total of thirty three different diseases were treated using herbal remedies. This diversity in diseases treated is an indication that medicinal plants have a real potential of meeting the varied healthcare needs of residents of a rural village like Kikuku. Medicinal plants have been shown to be the base of healthcare systems in many societies [1] and therefore their use in the treatment of a wide range of diseases as elucidated in this study goes further to show their centrality in meeting healthcare needs of rural populations. Most of the disease conditions cited by our informant (60.6%) were treated using more than a single species. Malaria, like in previous studies done in Kagera region [3, 4], was treated with the highest number of different plants. The use of such a wide variety of plants for the treatment of one disease alone could be an indication that this disease is prevalent in the study area [1]. It could also be due to the availability of a wide variety of herbal medicines indicated for the treatment of the disease [69]. It is not surprising that there were a comparable high number of plants that were used for the treatment of bacterial infections given that these are commonplace indications largely associated with personal hygiene and care. From the results, it seems like malaria and bacterial infections constitute the biggest proportion of health problems common in this part of Tanzania.

Decoctions were cited as the most commonly used dosage form. In the majority of cases it involved directly boiling the part to be used (e.g. leaves) in water or first pounding the part and then boiling as in the case of Senna occidentalis where the roots were pounded before boiling. Boiling is considered to be effective in extracting plant materials besides also preserving them longer compared to using cold water [70]. However it also has its drawbacks in that if careful attention is not paid to the time needed for boiling some ingredients may be damaged, especially with prolonged boiling and useful aromatic ingredients present may also be lost through dissipation into the air [71]. Our results show that making of concoctions to treat a given ailment was not a common practice with the healer we interviewed. She only treated three diseases using concoctions. An interesting method of preparation was that of Amaranthus spinosus leaves which were boiled with fresh cow milk and drank as a remedy for peptic ulcers.

Close to 43% of the curative claims concerning plants used as traditional medicines in Kikuku were well supported by literature based evidence. This finding is consistent with two previous ethnomedical studies carried out in the Kagera Region [3, 4]. The correlation of the traditional uses of some of the plants with their known phytochemical and pharmacological properties lends credence to some of the ethnomedical claims.

Conclusion

This study shows that the Euphorbiaceae and Asteraceae are important in the indigenous healthcare management in Kikuku village given that they emerge as the families with the highest number of species used as traditional medicine. Some of the correlations observed between traditional plant use in Kikuku village with scientifically proven phytochemical and pharmacological properties of the plants and also with reports of similar use elsewhere, suggests that herbal remedies constitute an important and effective component of the healthcare system in Kikuku village and whose use therefore needs to be encouraged and promoted. However more in-depth phytochemical and pharmacological studies are necessary to support the use of the plants documented in this study.