Schistosomiasis is a parasitic disease caused by dioecious digeneans of the genus Schistosoma. It is a water–dependent disease of considerable medical and veterinary importance in tropical and subtropical regions in terms of prevalence. It is estimated that more than 236.6 million people in 78 countries required preventive treatment in 2019 [1]. Sub–Saharan Africa’s contribution to schistosomiasis prevalence accounts for 90% of cases [2].

In Mali, there are two major human–influenced species of schistosomes: S. haematobium and S. mansoni, which thrive around large artificial water supply structures (Markala, Selingue, and Manantali dams), small reservoirs on the Dogon plateau or around ponds, and in villages along the Senegal and Niger rivers. Therefore, schistosomiasis is endemic throughout the country [3,4,5]. While S. haematobium is the most common schistosome because of the wide–spread distribution of its intermediate host, Bulinus truncatus in all biotope types [6,7,8], S. mansoni distribution is rather focused on certain localities, such as the Office du Niger, Sélingué, and Baguinéda (Bamako) [3]. However, although it is a classically rural disease, urban areas are not spared from it either. Infections due to S. haematobium and S. mansoni have been reported in Bamako since 1951 [9]. Recently, prevalences of 14.7% and 1.5% have been recorded for S. haematobium and S. mansoni, respectively [10]. In response to schistosomiasis endemicity, Mali was one of the first countries in sub–Saharan Africa to set up the National Schistosomiasis and Soil–Transmitted Helminthiasis Control Programme (NSCP) in 1982. Thanks to its effectiveness and ease of implementation, mass drug distribution (MDD) with praziquantel (PZQ) for schistosomiasis has become an integral part of all schistosomiasis control programs. In Mali, the strategy was adopted in 2005, initially in highly endemic areas, before being extended to all other endemic zones. Despite the implementation of this program some twenty years ago, residual pockets have been reported in some areas of the country, such as the Senegal River Basin [11] and around Bamako [10,12]. In terms of epidemiology, social and environmental vulnerabilities contribute to the persistence and increase in schistosomiasis. The epidemiology of schistosomiasis is greatly influenced by ecological and human factors [13]. Ecological changes resulting from the presence of water points influence the survival, dispersal, distribution, and abundance of cercariae and host snails due to changes or modifications in habitat conditions. This is the case in the district of Bamako, which is crossed by numerous rivers such as Sogoniko, Bankoni, Farako, or Woyowayanko flowing from the Niger River. Elsewhere, other human factors likely to influence the epidemiology of schistosomiasis include urbanization. The role of urbanization in neglected tropical diseases (NTDs) has raised attention in the past decade because, in living memory, for the first time more people have lived in urban areas than in rural areas (56 and 44%, respectively), and, by 2050, this number is expected to reach 66% of the world population [14]. Even if this phenomenon is usually associated with economic progress and better social and health conditions, in developing countries, such progress is not synonymous with better living conditions [15]. In Bamako, for example, urbanization has transformed the quality of life of the inhabitants of the quarter of Missabougou, with the construction of the city’s third bridge, a modern hospital, an increase in the number of basic social services (schools, community health centers, road infrastructure, etc.), and also the development of the canal branching off from the River Niger and running alongside it as far as the village of Baguineda, 30 km away. Unlike Missabougou, in another neighborhood, Taliko, the persistence of the rural lifestyle, such as the use of surface water for domestic purposes (dishes, washing, pickling, etc.), added to poor sanitation created favorable conditions for the transmission of schistosomiasis. How do these changes affect the transmission of the disease in the two quarters of Bamako district, Missabougou and Taliko? The latest study to examine the impact of a change in the environment on transmission dates from 2010, where sanitation projects in the capital have made it possible to improve some of the city’s water, which are potential breeding sites for snails, the intermediate host of schistosomes [10]. This study aimed to describe sociodemographic and environmental risk factors for schistosomiasis among schoolchildren in two different settlements in the Bamako district. In addition, taking these results into account in local social project development could help break the schistosome transmission cycle.

We recorded an overall prevalence of 34.4% versus 2.9% for S. haematobium and 12.07% versus 4.3% for S. mansoni for the peri–urban area (Taliko) and an area subjected to social and environmental changes (Missabougou), respectively. This prevalence of S. haematobium (18.2%) and S. mansoni (8.1%) was higher than that (14.7% and 1.5%) previously reported throughout the Bamako district by Dabo et al. (2015). Likewise, the prevalence of S. haematobium recorded in Taliko in MIV (34.4%) was slightly higher than that in 2015 (31.1%) in the same area but in April and November, respectively. This consistency or slight increase in prevalence indicates the persistence of the disease due to the active nature of the parasite within the population. Males in Taliko were significantly more heavily affected (p = 0.001). This result is similar to those described in the same area [10], but different from that reported by Agniwo et al. (2022) in the Kayes region of Mali. Globally, males were more heavily affected by S. haematobium than females (Table 1) (p = 0.003). The influence of gender on the prevalence or intensity of schistosomiasis is debatable and varies from one study to another. The results are sometimes higher in women, for example, in the Bandanyenje region (Zimbabwe) [18], and sometimes lower, such as in the Oromia region (Ethiopia) [19,20]. In the Kayes region (Mali) [21] or in southern Nigeria [22], there was no difference in disease prevalence between genders. The differences between genders in terms of prevalence or intensity could be explained more by behavioral differences (nature and intensity of water contact activities) than by immunological differences, according to a meta–analytical approach based on data from 23 schistosomiasis–endemic countries [23].

The high prevalence and intensity rates observed in Taliko compared to Missabougou would be mainly due to the various changes that have occurred or are underway in Missabougou (cf. Materials and Methods). The cleaning of the banks of the canal leads to the destruction of the habitat of snails (aquatic vegetation and debris of all kinds dumped into the bed). A similar experiment was conducted in another quarter of Bamako, Niomirambougou, in 2010 with the cleaning and development of the banks of the Farako River as part of the improvement of the living environment of the city of Bamako. Prior to intervention, the prevalence of urogenital and intestinal schistosomiasis and that of double infection were 89.8%, 30.2%, and 65%, respectively, in schools along the river [24]. Children frequenting the river had a higher prevalence of S. haematobium and presented more hematuria with a high parasite load in Taliko (p < 0.05). This result is opposed to that reported most recently by Agniwo et al. (2022) in the Kayes area, but is consistent with several other studies [10,25]. All children with macroscopic hematuria attended a school close to the river (p = 0.018). The short distance from habitats and schools favors access to contaminated water for children who easily engage in risky activities such as swimming and various practices. However, the influence of distance on schistosomiasis transmission is controversial. While some studies are in agreement with a positive association between short distance and infection [10,26,27], others argue the opposite [28]. We, however, believe that in addition to distance, some other factors, including sanitation in some communities like Taliko, where the river banks were used as garbage dumps, could have contributed to the higher level of infection. Children accustomed to urinating in water were more affected, with a higher load (p < 0.05). The fact that children were in contact with water for a long time, which means being exposed to cercariae for a long time, would be responsible for their infection. This factor not only exposes the children but is also a source of contamination of the water through the infected urine they simultaneously discharge into the water.

In our survey, sociodemographic parameters showed that children aged 11 to 14 in Taliko, the peri–urban area, had significantly more macroscopic hematuria than younger children (p < 0.0001). The great mobility of older children compared with the youngest children under parental control could explain this observation. We also noted that among children with bladder pain, pollakiuria, and dysuria, boys were significantly more affected in Taliko (p < 0.05). The same results were observed in Missabougou for pollakiuria and dysuria (p < 0.05). This observation supports several studies that have reported clinical signs in children in schistosomiasis–endemic areas [11,29,30].

Clinical and parasitological parameters revealed parasitemia in children presenting with macroscopic hematuria of high intensity. This finding is supported by several reports that show hematuria to be the pathognomonic paraclinical sign associated with the presence of S. haematobium eggs in urine [11,29,31]. Children with bladder pain were in the majority (p = 0.0001), in contrast to those with dysuria in Taliko, as recently reported in a study in the Kayes region, where these signs were reported in over 45% of affected children [11]. Overall, the prevalence of intestinal schistosomiasis was 8.1%, varying from 12.0% in Taliko to 4.3% in Missabougou. This means that, despite the environmental changes in Missabougou, especially the canal clean–up, transmission is still ongoing. In this case, there could be other sources of contamination apart from the canal. Further investigation will be useful to address this issue.

In terms of limitations, urine and stool analysis techniques are the gold–standard methods used in parasitological investigations. However, the sensitivity of these methods could be increased by increasing the number of urine samples and the number of Kato–Katz slides. On the other hand, an epidemiological study of schistosomiasis should always be accompanied by a malacological investigation to identify snail intermediate hosts and determine their natural infestation rates. Such a study could not be carried out because of the drying up of water points at the time of the survey, particularly in Taliko.

The study showed that both S. haematobium and S. mansoni still persist in the two study areas, especially in the peri–urban area, despite the annual mass drug distribution of praziquantel. The results show that the infection was more prevalent in Taliko (a peri–urban area) than in Missabougou (an area subjected to environmental changes). Visiting water points in Taliko for many human water contact activities, such as swimming for children, appears to be one of the most important risk factors for the maintenance of infection. In the absence of public swimming pools for children, cleaning the banks of water points could significantly reduce the risk of infection, in addition to providing health education and a proper supply of drinking water to the population.