Semi-field and field trials to control Biomphalaria alexandrina and Bulinus truncatus, intermediate host snails of schistosomiasis in Egypt by the plant molluscicide Luowei/TDS 4%

Abstract

Controlling the snail intermediate hosts of schistosomiasis is an efficient and rapid method for reducing or eliminating the transmission of this disease. The present study aimed to assess the molluscicidal activity of Luowei/TDS 4% against Biomphalaria alexandrina and Bulinus truncatus under semi-field and field conditions in Egypt. Moreover, its effect on Schistosoma mansoni miracidial viability and infectivity to B. alexandrina snails and on cercarial production from infected snails were evaluated. In the present study, miracidia of Schistosoma mansoni and S. haematobium were exposed to sublethal concentrations of Luowi/TDS 4% and miracidial mortality rates in the test and control groups were recorded. The effect of exposure to LC10 and LC25 of Luowei/TDS 4% after 1, 2 and 3 weeks of B. alexandrina infection with miracidia on their cercarial production was determined. The molluscicidal activity of 2LC90Luowei/TDS 4% against B. alexandrina and B. truncatus was tested under semi-field and field conditions. Luowei/TDS 4% exhibited a promising molluscicidal potency against B. alexandrina and B. truncatus as their LC90 values were considerably low, 2.851 and 1.936 mg/L, respectively, after 24 h of exposure. Moreover, infection rates of B. alexandrina with S. mansoni and cercarial production from snails exposed to LC10 and LC25 of Luowei/TDS 4% post miracidial exposure were reduced. Moreover, Luowei/TDS 4% at semi-field and field trials proved to be a potent molluscicidal agent against schistosomiasis intermediate host snails as mortality rates of free and caged sentinel snails from these trials were considerably high ranging from 87% to 100% after 24 h of treatment with 5.702 mg/L (2LC90 for B. alexandrina snails). Luowei/TDS 4% should be considered as a candidate molluscicide in schistosomiasis control programs. Implementation of this plant molluscicide in operational schistosomiasis control strategies will minimize the ecological side-effects associated with replacing synesthetic chemicals.