Ethnomedicine of the Kagera Region, north western Tanzania. Part 2: The medicinal plants used in Katoro Ward, Bukoba District

Katoro is a ward within Bukoba district and lies on the south west of Bukoba town and situated at 1° 23' 59'' South, 31° 30' 1'' East (Figure 1). Like the rest of the Bukoba district, the Katoro ward has good rainfall and good vegetation cover that provides abundant resources for traditional medicines.

Independently, the research team established contact with three informants (Issack Kato, Maruzuku Mazimpaka and Hajat Nuria Kyejo) who practice traditional medicine in Kashaba village in Katoro. A field visit was, thereafter, made to the area between 28^th February and 2^nd March, 2008. During this visit ethnomedical information was collected using semi-structured interviews [6] as the team walked, accompanied by the informants, through the banana farms, roadside and surrounding bushes and thickets of Kyamlaile and Kashaba villages. Voucher specimens were made for all plants collected and these 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 that of the Institute of Traditional Medicine, Muhimbili University of Health and Allied Sciences.

Literature information was retrieved from the NAPRALERT data base at the School of Pharmacy, University of Illinois at Chicago. The strength of information obtained from the informants was evaluated based on its agreement with similar therapeutic claims in literature from elsewhere or evidence in literature of laboratory results that support the claims.

A total of 33 plant species belonging to 31 genera and 19 plant families were documented (See additional file 1)). The largest proportion of medicinal plants collected belonged to the family Asteraceae (21%), followed by Fabaceae (12.1% each) and Euphorbiaceae (9.0%). The main source of these plants in terms of number of species were trees (30.3% of the total number of species) followed by shrubs (39.4%) and herbs (21.2%). The remaining 9.09% were climber herbs and shrubs.

A wide variety of medical conditions were treated using remedies made from medicinal plants. Most of the plants used had more than a single therapeutic use. For example, Draceana steudneri was used for treating fibroids, splenomegaly and asthma. On the other hand, many diseases were also treated using a wide range of plants. Malaria for example, was treated using Senna alata, Clerodendrum myricoides, Dalbergia nitidula, Eriosema psoraleoides, Hygrophylla auriculata, Rhus vulgaris and Vernonia amygdalina. The most frequent ailments treated with medicinal plants were those categorized here as specific diseases/conditions (Table 1) comprising conditions like malaria, dysentery, cancer, yellow fever etc. and were treated using the largest number of remedies (23.8% of all remedies). On the lower end, 1.5% of the remedies were used to treat eye diseases, 2.98% cardiovascular and circulatory diseases (e.g. anemia), 4.47% respiratory tract infections (e.g. chest pains) and 4.47% skeletal muscular problems (e.g. body spasms). Reproductive problems like difficulties to conceive and low libido were treated using 14.2% of all the remedies used.

The plant parts used for making herbal preparations were the roots, leaves, stem bark, root bark, pods and other aerial parts. The leaves were the most frequently used (20 species) followed by the roots (13 species), and stem bark and other aerial parts (each 4 species). Other parts like the pods were also used, for example in Kigelia africana and the root bark in Parinari curatellifolia, but rarely.

Mono therapies based on preparations made from a single plant were the most dominant, although many remedies where more than one plant was used were also common. Those that involved the use of two species included, for example, the boiling of Carissa tomentosa roots with the bark of Elaedendron buchananii or powders of the two being mixed and taken with tea or mixed with roots of Tragia furialis for the treatment of hernia, backache or taken as an aphrodisiac. Others included a decoction made from boiling the roots of Combretum collinum and Rhus vulgaris being drunk for the treatment of dysentery while another made from boiling the leaves of Dalbergia nitidula with the stem bark of Sapium ellipticum was used to treat malaria. Fresh leaves of Dichrocephala integrifolia were pounded with the leaves of Ageratum conyzoides and the juice squeezed out and applied to the eyes as an eye drop while for the treatment of indigestion, the leaves of Hoslundia opposita were mixed with the leaves of Ocimum basilicum, boiled and the decoction drunk. A decoction made from boiling the leaves of Pappea capensis with those of Vernonia brachycalyx was drunk for the treatment of backaches and to treat chickenpox, the leaves of Rhus natalensis mixed with those of Vernonia amygdalina were boiled and the decoction drunk. Treatments that involved the use of three or more plants in combination included, for example, the pounding of the roots and/or leaves of Desmodium salicifolium, Elaeodendron buchananii and Tragia furialis then boiling and taking the decoction as an aphrodisiac. Others included the treatment of skin rashes and joint pains and relieving of feet from burning sensations by applying the root or stem bark powder of Maytenus senegalensis mixed with the root powders of Rauvolfia vomitora, Parinari curatellifolia and Ozoroa insignis in a fat base. The treatment of yellow fever involved pounding and boiling the leaves of Trema orientalis with those of Combretum collinum and Erythrina abbysinica and taking the decoction. Backache was also treated using a decoction prepared from a combination of four different species. The decoction was made by boiling the root powder of Tragia furialis mixed with that of Elaeodendron buchananii or Spathodea campanulata and Carisa spinarum and then drunk or the powders were simply mixed with water and taken. A second treatment of malaria involved taking a decoction made from the leaves and/or roots of Vernonia amygdalina mixed with the stem bark of Rhus natalensis and the leaves of Dalbergia nitidula, Desmodium salicifolium and Eriosema psoraleoides. The most common methods used to prepare most of the therapies were making of decoctions (46.4%), pounding (14.2%), squeezing (10.7%), making infusions (8.9%), burning (7.1%) and grinding to powder (5.4%).

Out of all the plants used by traditional healers in Katoro, the uses of 47% of them (16 out of 34 species) are supported by reports of similar uses or proven biological activity in the literature. There were no reports of toxicity for any of the species except for Ageratum conyzoides reported to have caused toxicity to sheep [7]. The plants whose therapeutic claims are well supported by the literature include Ageratum conyzoides [8‐10], Bidens pilosa [11‐14], Boerhavia diffusa [15], Capparis tomentosa [16], Cassia alata [17‐19], Clerodendrum myricoides [20, 21]. Others are Combretum collinum [22], Dichrocephala integrifolia [23], Flueggea virosa [24, 25], Hoslundia opposita [26], Jatropha curcas [27, 28], Lantana camara [29‐31], Melanthera scandens [32], Microglossa pyrifolia [33, 34], Rubia cordifolia [35‐37] and Vernonia amygdalina [32, 38, 39].