The study was conducted in Southern Chad and received approval from the national bioethics committee under the reference number 585/PR/PM/MESRI/ SEESRI/SG/2016. The study protocol, along with consent documents, was submitted to the committee. Comprehensive information about the study’s purpose was provided to the participants. Written informed consent was obtained from all individuals, including the parents or guardians of minors under the age of 18.

The research focused on two areas in Southern Chad, Kouh-Est and Grand-Sido ( Figure 1 ), both part of the Sudano-Guinean savannah geo-ecological zone, characterized by an annual rainfall of 1000 mm to 1300 mm [15] . The rainy season runs from May to October, with the dry season extending from November to April.

The Kouh-Est area, also known as the Mandoul sleeping sickness focus, is located in the Logone-Oriental province at N8˚12.375' E17˚08.063'. This historic sleeping sickness focus, demarcated in 2003, spans approximately 15 km by 20 km and houses around 20,000 inhabitants [16] . With ongoing population growth, recent surveillance estimates suggest 38,674 people now living in 117 villages in this region [17] [18] . The Mandoul riverbanks, shaded by riparian and gallery forests, provide a cool environment conducive to tsetse flies, which thrive in this area as well as snails and other parasite vectors.

Grand-Sido, located on the border with the Central African Republic (CAR), includes the Maro sleeping sickness focus (N8˚24.807'E 18˚46.139') in the Moyen-Chari province. This region is crossed by multiple rivers, including the Chari and its tributary Grand-Sido, which delimit the CAR border. A 2016 geographic survey by the “Programme National de Lutte contre la Trypanosomiase Humaine Africaine” (PNLTHA) and “Institut de Recherche en Elevage pour le Développement” (IRED) indicated a population of 14,532 across 45 settlements [19] , with additional seasonal nomadic pastoralists [13] .

The selection of the two areas is based on an ongoing vector (tsetse) control operation, with the annual deployment of Tiny Targets that began in 2014 in Kouh-Est, whereas no similar operations were implemented during the surveys in Grand-Sido. The study adopts the WHO Conceptual Framework of SDOH, comparing an area with an ongoing vector control program (Kouh-Est) to one without (Grand-Sido).

Participants were eligible for inclusion if they were aged between 5 and 90 years and resided in the Kouh-East or Grand-Sido. Children under 5 and elderly individuals above 90 years were excluded from the study due to ethical, practical, and safety considerations related to invasive procedures such as blood sampling, which were conducted as part of the survey. Additionally, individuals who declined to participate or were not residents of the specified regions—Kouh-Est and Grand-Sido—were also excluded.

The study was a descriptive, quantitative, population-based, cross-sectional survey, using a face-to-face questionnaire to collect data.

Surveys were conducted in February 2017. In both areas, eight villages were randomly selected, including nomadic, semi-nomadic, and sedentary communities. The survey teams introduced themselves to village heads, explained the study in local languages, and obtained household lists. Households were numbered, and 6 to 16 were randomly selected in each village, with all members from each household invited to participate. The number of participants varied depending on village size and participation. Participants completed questionnaires with the assistance of local interpreters.

Sample sizes were calculated using open-source software, OpenEpi [20] and Raosoft [21] . Based on the populations of Kouh-Est (38,674 in 114 settlements) [18] and Grande-Sido (14,532 in 45 settlements) [19] , the required sample sizes for the study were 381 and 375 respectively, with a 5% margin of error and a 95% confidence interval.

The questionnaires were adapted from the Chadian Demographic and Health Survey [10] , the Tanzania Demographic and Health Survey [22] , and Food and Nutrition Technical Assistance [23] . Three forms (Annex 1, 2 and 3) were used. Household questionnaire (1) concerns primarily household heads or their designated caretakers. On the individual questionnaire (2) data on age, gender, marital status, education level, and occupation/income were collected. Health status questionnaire (3) documented participants’ knowledge on VBPDs and their prevention methods as well as water supply and the condition of water storage and treatment.

Local facilitators, fluent in local languages and specifically trained for this study, carried out the translation of the questionnaire. This approach effectively bridged language barriers and fostered trust, encouraging more accurate and reliable responses. Additionally, occasional follow-up interviews were conducted to assess the consistency and reliability of self-reported data.

The general characteristics of the study population were described using standard descriptive statistics including means, standard deviations, and frequencies with the 95% Confidence Interval. The chi-square (χ2) test was applied to analyse categorical variables and assess differences in literacy and knowledge of VBPDs between groups. Statistical significance was set at p < 0.05. SPSS v 22.0 (IBM, USA) was used for the statistic evaluation, GraphPad Prism 7.0 for constructing the graphs, and Microsoft Excel for managing raw data.

Eight villages/settlements were visited in the Kouh-Est, while nine in the Grand-Sido, including one military camp having a unit close to one of the visited villages ( Supplementary Table 1 ). The lowest number of participants in a village was recorded in the military camp (n = 19) and the highest in a nomadic settlement (n = 73).

202 households were randomly selected ( Table 1 ) in 17 villages overall ( Supplementary Table 1 ). Males were predominantly represented as heads of households, either in monogamous (55.0%; 95% CI: 48.5 - 61.9%) or polygamous households (20.8%; 95% CI: 15.3% - 26.7%). The few females recorded as heads of households (9.9%; 95% CI: 5.9% - 13.9%) were mostly widows (35.0%; 95% CI: 15.0% - 55.0%; n = 7), divorced (35.0%; 95% CI: 15.0% - 55.0%; n = 7), or single (30.0%; 95% CI: 10.0% - 50.0%; n = 6). Regarding participants’ gender, males and females were almost equally represented, with 50.3% (95% CI: 47.1% - 53.6%) and 49.7% (95% CI: 46.4% - 52.9%), respectively.

¹Primary sector includes agriculture, livestock farming and fishing. ²Secondary sector includes military, policemen, civil servant workers, industry workers, and construction’s workers. ³Tertiary sector includes services and trade, local drinks producers and transformers. ∗significant difference; ∗∗very significant; ∗∗∗highly significant.

Sedentary populations were more highly represented than nomadic ones ( Table 1 ). The nomadic populations were primarily pastoralists, entering these areas in search of grass and crop residues for their livestock, sometimes staying for more than six months. In addition to these two population groups, a military camp in the Grand-Sido area was also included in the survey.

Regarding socio-professional activities, only adults over the age of 18 (n = 516) responded to this section. The primary sector, including agriculture, livestock, and fishing, accounted for 84.1% (95% CI: 80.3 - 91.1%) of the participants’ activities.

The number of participants who responded to each section of the questionnaire varied. Some participated in the entire survey, while others decided to skip certain sections for their own reasons. Of the 890 individuals registered for the study, 807 (90.7) met the inclusion criteria.

Of the 820 participants, 671 provided responses to the questionnaire regarding their literacy levels (for individuals above six years old). Literacy levels reflect the highest level of education attained by each participant, meaning those with secondary education were not included in the primary level category. The average rates for the two areas were as follows: 36.7% (95% CI: 33.0% - 40.4%) for non-educated, 47.7% (95% CI: 43.9% - 51.5%) for primary school level, 14.5% (95% CI: 11.9% - 17.3%) for secondary school level, and 0.3% (95% CI: 0 - 1.1%) for tertiary level ( Figure 2 ). Most of the villages did not have conventional and established schools, and where schools did exist, they typically only provided primary education.

There was a statistically significant difference (p < 0.001) between the two areas in the proportion of participants who had no formal education ( Figure 3(a) ). Among those who were educated, 48.8% and 46.9% stopped at the primary level, while 21.1% and 9.6% respectively reached the secondary level (p < 0.001). Only 0.7% were undergraduate, and 0.8% participants had exclusively religious education.

In terms of nomadic participants, significantly higher had no formal education (71.4%) compared to sedentary participants (28.1%) ( Figure 3(b) ). The difference was statistically significant including both primary and secondary education levels (p < 0.0001).

Regarding participants’ knowledge of the vectors responsible for common diseases in the areas, both the Kouh-Est (Mandoul) and Grand-Sido (Maro) populations demonstrate a high level of awareness about malaria, with over 65% of respondents in both regions recognizing the disease vector ( Figure 4(a) ). However, the awareness of trypanosomiasis is significantly lower in Grand-Sido compared to Kouh-Est. Kouh-Est shows significantly higher awareness of trypanosomiasis (69.4%) compared to Grand-Sido (52.9%) (p < 0.001). Both regions exhibit very low awareness of river blindness, with less than 1% of respondents in each region aware of the disease vector.

No statistically significant difference in knowledge about mosquito vectors was observed between sedentary and nomadic participants ( Figure 4(b) ). However, a difference emerges when considering knowledge of tsetse fly vectors.

In light of these findings, an exploration of the protective measures used against insect vector bites was evaluated. For protection against mosquitoes, 60% of participants reported using mosquito nets ( Figure 4(c) and Figure 4(d) ). In Kouh-Est, 12.8% relied on other protective methods, while 25.2% did so in Grand-Sido. Additionally, 19.4% of respondents in Kouh-Est and 10.1% in Grand-Sido did not use any protective measures, with this difference being statistically significant (p < 0.001).

In the studied population, most households were headed by men, both in monogamous and polygamous settings, while female-headed households were only 9.9% and mainly composed of widows or divorced women. This gender imbalance in household leadership is cultural in Chad and other sub-Saharan African countries, where patriarchal systems prevail, and men are typically seen as the heads of households [10] [24] . Similarly, in rural Mozambique, women tend to lead households primarily due to widowhood, divorce, or abandonment [25] . The low representation of female-headed households reflects regional socio-cultural norms that prioritize male leadership within family structures.

As an outcome emerging from the data, the level of literacy of the population in the two surveyed areas is generally low, with 36.7% of participants having no formal education and only 14.5% reaching secondary education. Taken alone, the participants from the Grand-Sido area are less educated (p < 0.001) than those of the Kouh-Est, as well as nomadic than sedentary (p < 0.0001) ( Figure 3(a) ). Low access to school, due to the absence or remoteness of these structures, influences this situation. Most of the villages did not have established schools, and where schools did exist, they typically only provided primary education. This is one of the reasons for the low proportion of participants with secondary education. Factors such as geographic isolation, lack of infrastructure, and the economic necessity for children to work in pastoral or agricultural settings contribute to the lower education rates among rural populations [26] . Our findings also reflect a significant difference in literacy levels between sedentary and nomadic populations. The educational disparity between these groups often results from nomads’ mobility, making it difficult for their children to attend formal schools [27] [28] .

The study revealed that while most participants were aware of mosquitoes as vectors for malaria and tsetse flies as vectors for trypanosomiasis, fewer knew about the black fly’s role in transmitting river blindness. The disease might be less prevalent in the regions, leading to reduced public awareness. However, malaria remains the most recognized VBPDs, as evidenced in this study and across sub-Saharan Africa, largely due to extensive public health campaigns [29] and mosquito-net distribution. In rural areas where onchocerciasis is endemic community knowledge is often limited unless there are active disease control programs [30] . This underscores the need for more comprehensive education, sensitisation and outreach regarding less prominent VBPDs in both sedentary and nomadic populations. In the Mandoul sleeping sickness focus, regular screening campaigns and vector control operations conducted by the PNLTHA and IRED [17] [18] , [31] have contributed to greater awareness of the tsetse fly vector, as revealed in this study ( Figure 4(a) ). These efforts, along with the population’s own experiences with the diseases, have enhanced understanding of the impact of vectors in the region. Similar campaigns are needed to raise awareness of other less frequent but still present vectors.

In parallel, we evaluated the protection measures taken against malaria, the common VBPD that has an easy solution by being protected against mosquito’s bites. The study observed that 60% of participants reported using mosquito nets, which is consistent with a study conducted in 8 health districts across Chad, where 50.4% of individuals reported sleeping under insecticide-treated mosquito nets [32] . However, some proportions of the surveyed participants did not take any protection measures, which could be due to the health education and sensitisation issues. More sensitisation and improvement of health education is required.

The implementation and sustainability of vector control measures—such as insecticide-treated nets, community spraying, and Tiny Targets for tsetse flies—often depend on robust political will, sustained funding, and effective governance structures. These factors must be continuously encouraged and strengthened, with active involvement from both men and women of local community. However, women, often primary caregivers, may face limited access to health education or healthcare services, which can hinder their ability to prevent and manage VBPDs. By involving women in community engagement, VBPDs could be more effectively addressed through improved dissemination of health education, increased adoption of preventive measures, and enhanced participation in local health initiatives.

The primary sector, encompassing agriculture, livestock, and fishing, represents 84.1% (95% CI: 80.3 - 91.1%) of the populations’ activities in these rural areas. This finding aligns with previous surveys in the country [10] [15] , which reported that over 80% of rural inhabitants engage in agriculture and/or livestock farming. Additionally, more than 93 million cattle, sheep, goats, camels, and equines have been recorded across the country [33] . In trypanosomiasis-endemic zones, agriculture is widely practiced, and pastoralists frequently cross the border with the Central African Republic (CAR), seeking grass and crop residues for their livestock. These transhumance activities can last in the areas for over six months. The movement of livestock may play a significant role in the transmission of zoonotic diseases.

The health systems in both study areas are characterized by significant challenges, particularly in terms of accessibility and quality of care. Geographical disparities pose a major barrier. Health facilities are often concentrated in urban centers, leaving rural populations to travel long distances—up to 50 km—to access care, as seen in these two areas. This is especially problematic for emergency situations, maternal health, and chronic disease management. Studies in Sub-Saharan Africa have highlighted similar issues with rural communities facing longer travel times and delayed treatment [34] , leading to poorer health outcomes. Limited resources further exacerbate these challenges. Health facilities frequently lack essential medical supplies, diagnostic tools, and infrastructure, hindering their ability to provide adequate care. Additionally, the shortage of trained healthcare professionals limits the scope and quality of services available [35] . Such conditions are common in low-resource settings, contributing to suboptimal care and a lack of trust in the health system.

These combined factors—distance, inadequate resources, and personnel shortages—are compounded by poor road infrastructure, limited transportation options, and economic constraints. This results in worsened health outcomes for rural populations, including higher rates of preventable morbidity and mortality for VBPDs. Addressing these systemic problems is crucial for improving health equity and outcomes in these regions. This aligns with the World Health Organization’s emphasis on strengthening health infrastructure and human resources in rural areas to achieve equitable health outcomes [36] .