Bulinus Snails Control by China-made Niclosamide in Zanzibar: Experiences and Lessons

Abstract

Schistosomiasis haematobium is one of the most important, but often neglected, tropical diseases transmitted by snails of Bulinus in Zanzibar. Snail control by mollusciciding is the cornerstone in preventing the spread of schistosomiasis. In the past thirty years of schistosomiasis elimination in China, suspension concentrate of metaldehyde and niclosamide (MSCN) as a molluscicide has played a crucial role. However, there is no report about MSCN against Bulinus. Therefore, it is necessary to evaluate the effects of MSCN against Bulinus both in laboratory and field. The effects of MSCN were tested both in laboratory and field setting. The LC₅₀ of MSCN for Bulinus at 24 h and 48 h was 0.0758 mg/L, while the LC₅₀ wettable powder of niclosamide (WPN) at 24 h and 48 h was 0.400 mg/L. The lowest concentration of MSCN that killed all Bulinus after 24 h and 48 h was 0.200 mg/L and the highest concentration permitting snail survivals were 0.013 mg/L and 0.006 mg/L, respectively. In the field setting, one month after MSCN treatment, no living snails were found in any of the four treated ponds. MSCN had better molluscicidal effects for adult snails compared with WPN. The observation of the short-term effect (one month) and the long-term (three months) application showed that MSCN had a high molluscicidal effect against Bulinus and is therefore a powerful weapon in the control of Schistosomiasis haematobium.