Schistosomiasis as an urban disease: 13 years of studies in the neighborhoods of Salvador, BA, Brazil

BACKGROUND: Rapid urbanization in Brazil has shifted the epidemiological landscape of parasitic diseases, such as schistosomiasis and malaria. Although typically considered a rural infection, Schistosoma mansoni transmission persists in urban settings where sanitation and water access remain uneven. This study investigates the persistence and dynamics of urban schistosomiasis across neighborhoods of Salvador, Bahia, Brazil. METHODS: Between 2011 and 2024 cross-sectional surveys were conducted to identify neighborhoods with the highest prevalence in the major metropolitan area of Salvador, Bahia. A total of 6,863 residents provided demographic information and Kato-Katz examination of at least one stool sample. We conducted demographic surveys and stool examination on 3,964 individuals who were re-examined on up to three occasions at intervals ranging from 1-5 years. FINDINGS: The overall prevalence of initial examination was 7%. Regardless of treatment intervals, the community-wide prevalence declined by more than half and did not rebound. Apparent Incidence decreased to <0.5%/year following a second period of treatment. In nearly all communities, most infections occurred among individuals born in Salvador with no travel history outside the city. INTERPRETATION: Overall, the study provides one of the first individual-level longitudinal assessments of schistosomiasis persistence in an urban Brazilian setting, combining repeated parasitological surveys with demographic and environmental data across multiple neighborhoods. These findings indicate that schistosomiasis transmission in Salvador is largely local rather than imported. The decline in prevalence coincides with observed community-level improvements in sanitation and reduced contact with surface water. f prevalence rates were applied across the population of Salvador, this city could be considered one of the state's most important endemic areas.