Medicinal plants provide valuable resources for the majority of rural and urban populations in Africa, and constitute alternative sources for the treatment of diseases  (Badiaga,   2011).   Indeed,   several  therapies involve the exploitation of the active components of medicinal plants (Kidik Pouka et al., 2015). Traditional medicine is used by approximately 80% of the world population  to  solve  their  primary  health   care  problem(Fatima et al., 2015). Also, these plants provide invaluable resources for the pharmaceutical industry (Etame-Loe et al., 2018).

Respiratory diseases have spread throughout the world, particularly in Africa, and are extremely expensive to treat (Fatima et al., 2015). In Cameroon, respiratory diseases kill 14% of the population, while HIV kills 21% (Mpondo et al., 2017). The rural population has limited access to health infrastructure and conventional medicines, which are frequently expensive and toxic, and do not always represent an effective means of improving people's health (Kidik Pouka et al., 2015; Mpondo et al., 2017). In addition, seasonal variations, poverty and pollution are mostly responsible for the emergence of respiratory infections. Respiratory infections include: (1) infections of the upper respiratory tract such as colds, pharyngitis, and sinusitis. On the other hand, the infections of the lower respiratory tract include bronchitis, pneumonia, tuberculosis, and asthma (Baky, 2010; Aubry, 2020). Few studies on the use of plants to treat respiratory infections have been conducted, and the majority of them have focused on the lower respiratory tract (Focho et al., 2009; Mpondo et al., 2017). In the Littoral Region, ethnobotanical surveys on plants used against respiratory infections have been mostly carried out in markets in urban centers (Foze et al., 2021). As a result, there is a greater need for understanding of upper respiratory infections. The goal of this study was to identify plants and plant recipes used in the treatment of upper respiratory tract affections (URTA) in the Littoral Region's peri-urban and rural areas.

Study site

Littoral Region is an administrative unit located between coordinates 4.25°N and 9.31°E. It covers an area of 20.248 km² or 4.4% of the national area. It is bounded to the north by the Western region, to the south by the Southern region and Gulf of Guinea, to the east by the Central Region, and to the west by the South-west Region. The main ethnic groups found in this region are Abo and Bankon in the sub-division of Bonalea, Bandem and Mbang in the sub-division of Nkondjock, Bassa and Bakoko in the sub-division of Douala III, and Bassas in the sub-division of Pouma. There are also other populations here such as Bafia, Bamileke, Beti, and Bamenda, who came to trade or work in the agro-industrial companies. This study was conducted in 12 villages belonging to four departments. Within these, the villages were separated by at least 3 km (Figure 1).

Ethnobotanical surveys

Ethnobotanical surveys were done from August 2020 to January 2021 in twelve villages over the four sub-divisions stated earlier. The survey method used was the Popular Pharmacopoeia, in which the respondents were asked about the popular use of medicinal plants. Data   on   the   symptoms  or  physiological  effects  of  the diseases were collected from health staff, and complemented by a literature review (Betti and Lejoly, 2010). To harmonize with the international system, the diseases cited were distinguished into major groups, according to the latest classification of diseases proposed by WHO (2008). Interviews were conducted with 115 people of both sexes. Their age was classified into three ranges: 20-40, 40-60 and 60+. Questions used for the structured interview model were formulated in French or the local languages of Cameroon. An inventory of plant species and recipes used against upper respiratory diseases like pharyngitis, cold and sinusitis was collected. Botanical specimens were collected in the field with the help of local guides. They were identified in situ, using reference manuals. Unidentified specimens were taken to the Laboratory of Biology of Plant Organisms at the University of Douala, and to the National Herbarium of Cameroon (HNC).

Data processing and analysis

Data obtained were processed and analyzed with XLSTAT computer software version 2022.1.2.1256. A growth curve of the number of species identified was studied according to the number of people interviewed. The objective of the study is to find compatibility between the plant list obtained at the end of the surveys and all the plants used in pharmacopoeia against URTA. A graph was created in which the number of people questioned, divided into groups of ten after a random draw, was on the horizontal axis and the number of plants cited by each group was on the vertical axis. The Informer Consensus Factor (ICF) indicated the homogeneity of information provided by the study respondents. It ranged from 0 to 1, and was calculated by the formula:

ICF = (Nuc – Nsu) / (Nuc – 1)

where Ncu is the number of usage citations reported in each disease category, and Neu is the number of species used for the treatment of each disease (Ugulu et al., 2009).

Socio-demographic characteristics of respondents

At the end of the surveys, 115 respondents have been identified. They were 81 women and 34 men. The dominant age group was 40-60 (44%), followed by 20-40 (37%), and 60+ (19%). Three major ethnic groups were identified after the investigations: Sawa was the most represented group with 56 (48.69%) people, followed by Bassa with 27 (23.48%) people, and Bamileke with 23 (20%) people. The other ethnic groups, Bafia, Beti, and Tikar represented 7.83% of the respondents (Figure 2).

Species identified

The inventory of medicinal plants revealed 39 species belonging to 36 genera and 21 families. Lamiaceae was the most represented family with six species. Asteraceae had four species, Myrtaceae and Rutaceae recorded three species. Anacardiaceae, Araceae, Caesalpiniaceae, Caricaceae, Costaceae, Crassulaceae, Huaceae, Musaceae, Piperaceae, Scrophulariaceae, and Malvaceae were the least represented with a single species each. Ocimum gratissimum had the highest number of citations (45), followed by Cymbopogon citratus (49 citations) and Citrus medica with 39 citations (Table 1).

Characterization of recipes

A total of 66 recipes were identified among the populations. Table 2 shows the recipes and their characteristics given by each respondent. It shows that the decocted and triturated leaves of O. gratissimum were the two recipes mostly shared by the ethnic groups, especially among Sawa (26 citations). The charred leaf of Elaeis guineensis and triturated leaf of Bryophyllum pinnatum are also recipes well-known by the Sawa group (100 and 64.5% citations, respectively). Thirty-eight (38) recipes received only one citation and are, therefore, considered unreliable.

Sawa group gave the highest number of recipes (48), followed by Bassa (27 recipes) and Bamileke (25 recipes). The calculated ICF showed over 0.5 values for the three major ethnic groups. For Sawa group, the ICF value was 0.74; for Bamileke and Bassa, the ICF value was 0.69. That means there was a relatively high agreement in the use of plants for the treatment of USRD. The ICF value was zero in the other ethnic groups. This means there was contradiction among the groups (Table 3).

The analysis of the evolution curve of the number of species according to the respondents showed a logarithmic shape; saturation was reached with 77 respondents (Figure 3).

Methods used in preparing the recipes

Ten methods were used to prepare the recipes. Decoction (39.16%) and trituration (38.11%) were the most cited preparation methods, followed by pressing (6.29%), carbonization (5.25%), or direct use (3.85%). The least used preparation methods were maceration and grinding (0.7% citations) (Figure 4).

Parts of plants used

Eight parts of plants were cited at the end of the surveys. Leaves had 195 citations (68.18%), while fruits and rhizomes recorded 17.42 and 7.32%, respectively. Flowers, buds and stems were the least cited parts, with two citations each (Figure 5).

According to the findings of this study, the Lamiaceae family has the greatest number of species used in the treatment of upper respiratory system diseases. The populations are also familiar with the plants used and their recipes. The  plant part with the highest number of citations is the leaves. This means that the overall pressure on the plant is low. Extensive research could be conducted on the most frequently cited species to identify their secondary metabolites.

The authors have not declared any conflict of interests.