Aspectos epidemiológicos e fatores associados à esquistossomose no município de Baldim, Minas Gerais: identificação de áreas prioritárias para vigilância com abordagem One Health

Abstract

Schistosomiasis is a neglected parasitic disease prevalent in tropical countries, primarily affecting low-income populations with poor sanitation. The municipality of Baldim, in Minas Gerais, has historically been endemic for schistosomiasis mansoni. Despite various interventions implemented between the 1950s and 1970s, the municipality still reports cases in the Schistosomiasis Surveillance and Control Program Information System (SISPCE). Considering the complexity of transmission and based on previous research findings, the World Health Organization (WHO) recommends integrated measures, such as the WASH (water, sanitation, and hygiene) approach and the One Health concept. Based on these recommendations, this thesis aims to describe the current situation of schistosomiasis mansoni in the municipality of Baldim from an integrated epidemiological perspective. In the human research, examinations were performed on elementary and high school students through the analysis of fecal samples (six slides per student, using the Kato-Katz method), in addition to the analysis of data from patients diagnosed by the PCE between 2008 and 2017. The students also completed socio-environmental questionnaires (sanitary conditions and water contact patterns) and participated in a pre- and post-exposure assessment of the educational material produced in this study. In the animal research, six malacological survey campaigns and evaluation of trematode infection in molluscs were conducted, with morphological taxonomic identification and molecular biology. Small wild mammals were also captured and collected for coproparasitological examinations and necropsies, with a primary focus on detecting S. mansoni. In the environmental research, water samples from sites where molluscs were present were analyzed to detect Escherichia coli (an indicator of fecal contamination) and S. mansoni eDNA by qPCR. Habitat characterization was performed using a standardized rapid assessment protocol. Animal and environmental health analyses were performed at 10 previously selected sites, based on current use by local communities and the history of schistosomiasis control interventions carried out between the 1950s and 1970s. The prevalence of schistosomiasis among schoolchildren in 2023 was 2.78% (6/216), with a low parasite load (EPG <100). The positivity rate recorded between 2008 and 2017 by the municipal surveillance system was 5.4%. Questionnaires revealed frequent exposure to bodies of water, such as washing vehicles (27.7%) and swimming (24.0%). Five species of Biomphalaria were identified, with B. glabrata being the most common. Of the 34 small mammals captured (18 Nectomys squamipes and 16 Didelphis albiventris), most were parasitized by nematodes, but S. mansoni was not detected. The parasite was also not detected in snails, although its DNA was identified in environmental samples through eDNA. All collection sites showed evident anthropogenic impacts and contamination by sewage and/or mammal feces. The educational intervention demonstrated a positive impact: knowledge about disease transmission increased from 58.2% to 95.7%; the identification of the snail as an intermediate host increased from 54.2% to 98.0%; and the perception of environments favorable to the presence of the snail increased from 78.1% to 94.4%. In spatial analyses, Kernel analysis allowed us to identify the distribution pattern of the residences of patients diagnosed by PCE (n=665) over a ten-year period. Kriging analysis revealed potential transmission areas, integrating human, animal, and environmental health variables. Both analyses highlighted the most urbanized areas, such as Centro, São Vicente, Vila Amanda, and Vargem Grande, as priorities. The findings indicated that the municipality of Baldim still has active transmission of S. mansoni, with a low endemicity profile and reduced parasite load. The research reinforces the need for intersectoral strategies that consider the interactions between human, animal, and environmental health to support more effective public policies for monitoring, controlling, and eliminating schistosomiasis.