Schistosomiasis remains one of the most widespread poverty-related neglected tropical diseases (NTDs) globally. It disproportionately affects individuals living in disadvantaged communities with limited access to potable water or adequate sanitation facilities [1,2]. An estimated 253.8 million people worldwide are affected, including 134.8 million school-aged children and 119 million adults [3]. According to WHO, disease-related mortality ranges between 1.7 and 4.5 million deaths [4]. It is further estimated that 91% of people requiring preventive chemotherapy for schistosomiasis reside in Africa [5]. Transmission is water-dependent and occurs following the infestation of humans or animals by flatworms of the genus Schistosoma [6]. The life cycle of the parasite involves two obligatory hosts: the definitive host (humans), where sexual reproduction occurs, and the intermediate host (freshwater snails), where asexual reproduction takes place, including the development and transformation of miracidia into cercariae. The latter are responsible for human infection after their release into freshwater [7].

In Africa, the intermediate host snail species of major medical importance involved in the transmission of human urogenital schistosomiasis belong to the family Planorbidae and the subfamily Bulininae, which comprises the single genus Bulinus spp. This genus includes 37 species classified into four groups: the B. africanus group (e.g., B. globosus), the B. forskalii group (e.g., B. forskalii and B. senegalensis), the B. truncatus/tropicus group (e.g., B. truncatus), and the B. reticulatus group (e.g., B. reticulatus and B. wrighti) [8]. Several studies in West Africa have demonstrated the involvement of Bulinus truncatus in the transmission of urogenital schistosomiasis in Senegal, notably in the Senegal River Basin and the Niakhar region [9,10,11], as well as in the Niger Valley (Niger). Other species such as Bulinus senegalensis, B. globosus, and B. umbilicatus have also been implicated in transmission in the Fatick–Niakhar region of Senegal, while Bulinus forskalii has been reported as a natural host in irrigated areas of Niger [12].

In Mali, schistosomiasis occurs in two forms: the intestinal form caused by Schistosoma mansoni and the urogenital form caused by Schistosoma haematobium. The latter is found across nearly the entire country, with an average prevalence estimated at approximately 38.3% [13,14,15], largely due to the widespread distribution of its two principal intermediate hosts, Bulinus truncatus and B. globosus [16,17]. Although B. forskalii and B. senegalensis have been collected (notably in the Dogon Plateau region and at the Office du Niger), they have not been shown to sustain active transmission [17,18]. The presence of B. umbilicatus has only been reported in Mopti, central Mali, in a pond named “Pague” adjacent to the town (Dabo, oral communication).

Several studies have demonstrated that abiotic parameters such as temperature, pH, conductivity, turbidity, and dissolved oxygen play a key role in the biology of Bulinus populations and thereby in the distribution of S. haematobium [1,19]. Beyond these, the epidemiology of schistosomiasis is also strongly influenced by ecological and anthropogenic factors [20]. In Mali, the climate is characterized by an alternation between a rainy season (June–October) and a long dry season (November–May), which strongly influences the abundance and distribution of snail. Rainfall promotes the formation of temporary ponds, rivers, and lakes favorable to intermediate host proliferation; however, during the dry season, human–water contact is concentrated around permanent water bodies [21]. High temperatures recorded between March and June further exacerbate these risks, reinforcing the seasonality of S. haematobium transmission [9,10] through increased exposure of local populations to contaminated water.

Ecological changes resulting from the presence of water bodies influence the survival, dispersal, distribution, and abundance of both cercariae and intermediate host snails. This is particularly true in the district of Bamako, in which numerous tributaries of the Niger River cross the city, including Sogoniko, Bankoni, Farako, and Woyowayanko [22]. Indeed, this site has already been the subject of several studies reporting overall prevalence levels of up to 18.2% for S. haematobium, with local prevalence reaching as high as 34.4% in Taliko [19,22]. Beyond their mere presence, the population dynamics of urogenital schistosomiasis intermediate host snails are strongly shaped by environmental, climatic, and anthropogenic factors, which in turn condition the risk of disease transmission. We hypothesized that, despite its urban context and ongoing control efforts, the transmission of urogenital schistosomiasis persists in Bamako due to favorable ecological conditions that sustain intermediate host snail populations and cercarial shedding. In this context, a better understanding of snail population dynamics, environmental drivers, and cercarial diversity is essential to inform targeted control strategies. In line with the World Health Organization (WHO) goal to eliminate schistosomiasis as a public health problem and interrupt transmission by 2030, this study aimed to assess (i) the seasonal and temporal variation in intermediate host snail populations of urogenital schistosomiasis and the physicochemical parameters of water, and (ii) the diversity of cercarial species shed in Bamako.

This study aimed to understand the temporal variation in the populations of snails, which are the intermediate hosts involved in the transmission of urogenital schistosomiasis in Mali. Our results showed both spatial and temporal variations in the physicochemical parameters of the water from the Niger River tributaries in Bamako. The water temperature ranged from 18.2 to 31.2 °C, with a mean of 24.5 °C across the two sites over the twelve-month study period. These temperatures were slightly lower than those reported in Benin [1]. The pH ranged from 5.1 in July 2024 to 9.1 in October 2024, with an overall mean of 7.05. The pH values observed in our study were higher than those reported in Benin [1,26], confirming the basic nature of the waters in the Niger River tributaries.

Electrical conductivity ranged from 52.7 µS/cm in Missabougou to 159.2 µS/cm in Taliko in February 2025, indicating a variation in the mineral content of freshwater in Bamako. These values fall within the low to moderate range typically observed for non-saline surface waters and were comparable to regional measurements. Analyses of the Niger River in Bamako have highlighted substantial spatial and seasonal variability in water quality, with conductivity influenced by urban inputs and seasonal flow [26]. The value observed in Missabougou (52.7 µS/cm) reflects low mineralization, consistent with waters relatively unaffected by dissolved inputs, whereas the value in Taliko (159.2 µS/cm) falls within the range reported for sites subjected to moderate anthropogenic influence or local mineral inputs (≈150–200 µS/cm) in field studies across West Africa [27,28]. These local differences may result from a combination of factors, including geological variations, domestic or agricultural effluents, and hydrodynamic differences between sampling points.

The relative density of snails, which serve as intermediate hosts of urogenital schistosomiasis in Mali, exhibited temporal and spatial variation. The mean densities observed in Taliko and Missabougou were 27 snails/person/15 min and less than 1 snail/person/15 min, respectively, with a minimum of 0 and a maximum of 124 snails/person/15 min recorded in Taliko. These contrasting patterns are consistent with observations reported elsewhere in West Africa (Niger, Mauritania, and Côte d’Ivoire), where the density of Bulinus and other intermediate host snails varies greatly between sites and across seasons. Studies using similar sampling techniques have reported both very-low-density sites and “hotspots” with high densities [6,29,30].

In Niger, systematic surveys along the Niger River Valley have reported substantial collections of Bulinus at certain sites during monthly sampling, reflecting local aggregations that could sustain transmission with significant proportions of infected snails [6]. Similarly, in Côte d’Ivoire and Mauritania, follow-up studies in urban and peri-urban contexts have shown that snail counts per collector/15 min could vary according to domestic inputs, habitat availability (aquatic vegetation, substrate), and hydrological fluctuations [29,30].

These analogies support the conclusion that Taliko represents a site with relatively high abundance at the time of sampling (indicating high local transmission potential), whereas Missabougou presents less favorable conditions for host aggregation. Our findings confirm that schistosomiasis, classically described as a rural disease, is also present in urban areas of Bamako, consistent with reports of expanding transmission foci in rapidly urbanizing cities [19]. The marked heterogeneity of snail densities between Taliko and Missabougou illustrates the existence of micro-hotspots, as previously reported in surveys conducted across the six municipalities of Bamako, where urinary schistosomiasis was found to be endemic in over 70% of schools. The immediate proximity of snail breeding sites and human activities constitute major risk factors, explaining the persistence of localized foci despite the area being in an urban environment [19].

In our study, Bulinus truncatus was predominantly collected in Taliko (476/645) and was extremely scarce in Missabougou (5/8), with continuous presence from January to May 2025 in Taliko, whereas in Missabougou, snails were detected only in February. These results are consistent with observations from N’Djamena (Chad), where B. truncatus exhibited marked seasonal fluctuations, with higher densities during the dry season or immediately following short rains [31]. Similarly, in Tiko (Cameroon), Bulinus spp., including B. truncatus, showed greater abundance during low-flow periods, while their density decreased during rainy or flood seasons [32].

These consistent patterns suggest that Taliko provides prolonged favorable ecological conditions for B. truncatus over several months, including suitable substrate, water availability, vegetation, and limited disturbances, while Missabougou appears to offer a less favorable habitat for snail development. This could be explained by the development of the banks of the Niger River in Missabougou (Figure 2A). In contrast to the predominance of B. truncatus observed in our study, Bulinus globosus plays a major role in South Africa (Ingwavuma, KwaZulu-Natal), where it accounted for nearly half of the collected snails and was widely distributed across sites [33]. These inter-regional differences highlight the importance of the ecological and climatic context in shaping intermediate host snail populations. Indeed, in Mali, hydrological and physicochemical conditions appear to favor B. truncatus, whereas in southern Africa, B. globosus occupies a dominant ecological niche and contributes more substantially to the transmission of S. haematobium.

The natural infection rate (NIR) observed in our study, ranging from 10 to 45%, with a peak of 45% in May 2025, falls within the ranges reported in several studies across West Africa. In Senegal, a study conducted in Niakhar reported infection rates of 15–42% for B. senegalensis and B. umbilicatus, depending on the locality [34]. In contrast, a meta-analysis covering multiple African countries reported lower mean infection rates for Bulinus spp., approximately 12% for B. globosus and 5–6% for B. truncatus, noting that these studies used different detection techniques (molecular assays or cercarial shedding tests) [35]. This contrast suggests that ecological conditions in Taliko in May 2025, including high snail abundance, favorable temperature, water availability, and human–water contact, were particularly conducive to infection. The meta-analysis also showed that detection by PCR revealed substantially higher infection rates (26.7%) compared to that found using simple cercarial shedding observation (4.5%) [35]. The use of molecular methods in our context likely contributed to the very high NIR observed. The difference between our elevated rate and lower rates reported elsewhere underscores the importance of seasonality, host density, and aquatic vegetation in the local dynamics of transmission.

In our study, variations in the infection of Bulinus spp. appeared to be strongly influenced by the physicochemical parameters of the water. Infected snails were mainly observed during the warmest months in Taliko (March–May, temperatures ranging from 27.9 to 30.6 °C) and, more rarely, in Missabougou in February at a lower temperature (19 °C). This observation is consistent with several studies showing that temperature not only influences snail population dynamics but also affects the development of intermediate hosts of Schistosoma [36]. Indeed, elevated temperatures (25–30 °C) favor Bulinus reproduction and cercarial shedding, whereas temperatures below 20 °C slow down the parasite’s life cycle [37].

Our results also show that periods of snail infection coincided with relatively high conductivity values (≥99 µS/cm) and pH levels above 6. This is consistent with observations from Benin and Côte d’Ivoire, where Bulinus proliferation was correlated with slightly mineralized waters exhibiting sufficient conductivity and mildly alkaline pH [1,38,39]. Similarly, in southern Africa, a study reported that moderate conductivity and pH values provide favorable conditions for snail survival and parasite transmission [33]. The monthly and spatial variations observed in Bamako may be explained by an interaction between local climatic conditions (seasonal temperature) and water physicochemical characteristics, which together influence both snail population dynamics and their susceptibility to Schistosoma infection.

In accordance of the significant impact of water conductivity on snail development, previous laboratory and field studies have shown that conductivity can influence the survival and reproduction of snails, the intermediate hosts of schistosomiasis, as well as the development of Schistosoma parasites [32,40,41,42]. Higher conductivity values may indicate greater nutrient availability for snails, promoting their growth and reproduction [40]. The conditions observed in this study suggest an environment conducive to the development of intermediate hosts and Schistosoma, which could increase the risk of schistosomiasis transmission in the Niger River tributaries in Bamako.

Cercarial shedding patterns of Bulinus spp. collected in Taliko (Bamako) showed a diurnal peak between 10 a.m. and 2 p.m., with lower emissions observed between 4 and 6 p.m. This contrasts with the findings of Sidibé et al. (2024) in western Mali, who reported peaks in the early morning (6–8 a.m.) and late afternoon (6–8 p.m.) [23]. Our results are consistent with Fryer and Probert (1988), who observed similar cercarial shedding patterns in Bulinus infected with Schistosoma haematobium in Nigeria [43]. These findings suggest that cercarial shedding patterns can vary depending on local conditions and human–water interactions specific to the site. The observed differences may be attributed to factors such as local water use habits, site ecological characteristics, and the snail species.

The genetic profiles of collected cercariae showed the presence of pure S. haematobium (Sh_Sh × Sh) regardless of site, time, or month of shedding. The majority of genotyped cercariae were observed in May 2025 (57.1%, p = 0.0001), suggesting a seasonal intensification of transmission, possibly related to more favorable environmental conditions for snails and parasite development. These results are consistent with Sidibé et al. (2024) in Mali, where cercarial density and shedding patterns varied according to human–water interactions and seasonal timing, with midday peaks for pure S. haematobium [23].

The absence of genetic variation according to shedding time indicates that, unlike hybrid schistosomes (S. bovis/S. curassoni × S. haematobium) [23,44], the transmission of pure S. haematobium strains may be less influenced by circadian rhythm and more by environmental factors such as temperature, pH, and water conductivity, which favor snail survival and infection [40].

Thus, the combination of genetic and ecological data highlights that seasonality and water physicochemical conditions are key determinants of the transmission dynamics of urogenital schistosomiasis in Bamako. These insights are crucial for effectively targeting control interventions, particularly during peak cercarial shedding months. However, this study has certain limitations. First, it was conducted at only two sampling sites, which limits the generalization of the findings to all urban and peri-urban areas of Mali. Second, the observation period, restricted to twelve months, does not account for interannual climatic variability that may influence snail population dynamics and schistosomiasis transmission. Finally, the absence of parasitological analyses on a broader range of snail species and the lack of complementary molecular tests may have limited the detection of potential co-infections or schistosome hybrids.

Interestingly, only pure genotypes of Schistosoma haematobium were identified in this study, with no evidence of hybrid forms, despite the increasing reports of Schistosoma haematobium × S. bovis or S. curassoni hybrids in West Africa. Several hypotheses may explain this observation. First, ecological factors specific to Bamako, such as the limited contact between livestock and water at the sampled sites, may reduce opportunities for interspecific transmission and hybridization. Second, the sampling design, which targeted specific sites and periods, may have limited the detection of rare hybrid genotypes. Third, although the combination of RD-PCR and ARMS-PCR is robust, it may have limited sensitivity for detecting rare or complex hybrid forms when present at low prevalence or resulting from successive hybridization events.

However, this study has certain limitations. Our sampling strategy followed standard malacological survey protocols (15 min timed collections per collector), but no formal sample size calculation or statistical power analysis was performed prior to the study. In addition, the number of sampling sites was limited to Bamako. Therefore, the findings should be interpreted with caution in terms of representativeness, as they may not fully capture the heterogeneity of all transmission settings in Bamako or other urban areas. Nevertheless, repeated monthly sampling over a 12-month period strengthens the reliability of the temporal trends observed in this study. A major limitation of this study is the absence of parasitological or epidemiological data on human infection. As a result, it was not possible to directly correlate snail infection rates and cercarial shedding profiles with the prevalence or intensity of infection in the human population. Such data are essential to confirm transmission intensity and to establish epidemiological links between environmental dynamics and human infections.

This study provides data on the comprehensive assessment of ecological and genetic factors influencing the transmission of urogenital schistosomiasis in Bamako, Mali. Our results show that Bulinus truncatus is the predominant intermediate host, with marked spatial and temporal variations, infection rates reaching up to 45%, and diurnal cercarial shedding patterns. Water conductivity significantly influenced snail populations and parasite development, while genetic analysis confirmed the presence of pure S. haematobium strains. The integration of ecological and molecular data highlights the importance of seasonality and local environmental conditions in shaping transmission dynamics. These findings provide essential information for effectively targeting control interventions, particularly during periods and at sites of peak transmission, to reduce the burden of urogenital schistosomiasis in urban settings. In-depth studies on snail population dynamics over multiple seasons will allow a better description of the impact of variations in mollusk density and infestation in the context of climate change.