PCR-based molecular identification of two intermediate snail hosts of Schistosoma mansoni in Cameroon.

Background: Snails of the genus Biomphalaria are intermediate hosts of Schistosoma mansoni, the causative agent of the human intestinal schistosomiasis. Two Biomphalaria species (Biomphalaria pfeifferi and Biomphalaria camerunensis) are involved in the transmission in Cameroon, where the disease is present nationwide. However, difficulty in the identification of both vectors impedes proper assessment of the epidemiological burden caused by each species. To overcome this issue, we designed a PCR-based molecular diagnostic tool to improve the identification of these species.

Methods: We analyzed the internal transcribed spacer 2 (ITS2) region of Biomphalaria ribosomal DNA (rDNA) using polymerase chain reaction amplification (PCR) and restriction fragment length polymorphism (RFLP).

Results: The amplification of the ITS2 region of Biomphalaria snails resulted in a 490 bp fragment and produced two profiles for each species after digestion with the restriction enzyme Hpa II. The profile 1 (Bc-HpaII-1: 212-bp and 139-bp bands) for B. camerunensis, was common in all the sampling points; the profile 2 (Bc-HpaII-2: 212-bp and 189-bp bands), was only observed in the Lake Monoun Njindoun sampling site. Biomphalaria pfeifferi profile 1 (Bpf-HpaII-1: 211-bp and 128-bp bands) was common in most of B. pfeifferi sampling points; the profile 2 (Bpf-HpaII-2: 289-bp and 128-bp bands) was only observed in Mokolo (Far North Cameroon).The second restriction enzyme TaqαI, revealed three band profiles, Bc-TaqαI-1 (243-bp, 136-bp and 118-bp bands) and Bc-TaqαI-2 (244-bp, 136-bp and 99-bp) for B. camerunensis and Bpf-TaqαI-1 (242-bp, 135-bp and 107-bp bands) for B. pfeifferi. Sequencing analysis revealed the occurrence of six haplotypes for B. camerunensis and three haplotypes for B. pfeifferi. The level of gene flow was low and the Biomphalaria populations were not in demographic expansion according to neutrality tests (Tajima's D and Fu's Fs).

Conclusions: The PCR-RFLP technique revealed genetic diversity in Biomphalaria snails, and the combination with the morphological method could improve the identification of B. pfeifferi and B. camerunensis in Cameroon. This could help focus on the infection to evaluate the transmission risk with respect of the different species and to develop efficient and cost-effective control measures.