Characterization of freshwater snail intermediate hosts of schistosomes in four communities from Osun State, Southwest Nigeria

Abstract

Aim: Freshwater snails of the genus Bulinus act as essential intermediate hosts of Schistosoma haematobium, a trematode parasite that causes urogenital schistosomiasis. The snails are widely distributed throughout Nigerian waters. Since species identification of the Bulinus snails is important for appropriate control strategies of urogenital schistosomiasis, this study therefore aimed at identifying the Bulinus species responsible for transmission of the infection in four communities located in an endemic Local Government Area of Nigeria. It also aimed at using restriction fragment length polymorphism (RFLP) as a more affordable method than sequencing to characterize Bulinus snails from schistosomiasis endemic regions in Nigeria. Methods: In this study, 100 freshwater snails morphologically identified as Bulinus species were collected from four communities located in a previously reported schistosomiasis endemic Local Government Area (LGA), namely Olorunda LGA in Oshun State, Southwest Nigeria. All snails were screened for schistosome infection using polymerase chain reaction (PCR) targeting the DraI gene. Molecular identification of the snails was done by PCR amplification of their entire internal transcribed spacer region including the 5.8S ribosomal RNA gene and RFLP. Results: Five of the 100 snails were positive for schistosome infection. PCR-RFLP profiles showed bands of different sizes for 26 other snails including the schistosome-infected ones. RFLP analysis showed that 11 of the snails belonged to the freshwater snails of the genus Physa while 13 belonged to the freshwater snails of the genus Bulinus, including Bulinus globosus (8) and B. truncatus (5). The species of the remaining two snails could not be resolved using the reference profiles from our previous studies. Conclusion: This study confirmed previous observations that limited morphological uniqueness within the Bulinus groups hinders their identification, and RFLP is a cheaper alternative method to sequencing that can be used by laboratories with limited resources for Bulinus species identification.