Malacological surveillance of the Schistosomiasis Control Program in the city of Salvador-Bahia between 2021 and 2023.

Resumo

Introduction: Since 2008, the Zoonosis Control Center of the Municipal Health Department (CCZ-SMS) has monitored water collections (CHs) in Salvador within the schistosomiasis control program. The objective of this study was to identify CHs with Biomphalaria spp. eliminating cercariae of the Schistosoma mansoni worm. Material and Methods: Malacological surveys were carried out at CH stations registered by CCZ-SMS to collect Biomphalaria ssp. in the period from 2021 to 2023. Due to basic sanitation works, urbanization, environmental modifications, or public security of the location, some CHs were excluded over time and others were registered after investigating a death registered in SINAN or resulting from an active search for snails. Field visits and snail collections occurred every six months, except in CHs with a history of cercariae elimination, which was monthly. The collection method used was that of Oliver and Schneiderman (1956), which employed the use of shells and storage pots with dechlorinated water to transport the snails to the laboratory. The collection time at each station was 10 minutes. The snails were diagnosed based on the 5-day classic cercariae elimination test (CCS). The water from the containers was transferred to Petri dishes and stained with lugol to visualize the cercariae under a stereoscopic microscope. Results: In 2021, 77 CHs were monitored, 37 (48%) with snails, accounting for a total of 7,187 snails collected. Of these, 16% (6/37) had snails eliminating cercariae (positive). In 2022, 84 CHs were monitored, 37 (44%) with snails, resulting in 6,919 snails collected, and 21.6% (8/37) of these were positive. In 2023, 88 CHs were monitored, 59 (67%) with snails, 6,429 snails were collected, and of these 8.5% (5/59) were positive. Three CHs were positive throughout the period, the others showed transient positivity. Furthermore, we observed a reduction in the number of snails collected over the years. Conclusion: By monitoring CHs, it was possible to identify schistosomiasis transmission foci in a large urban center. An integrated set of measures to combat schistosomiasis may be necessary.