Molecular characterisation of Biomphalaria spp in Egypt

Abstract

2. All species seem to be susceptible to S. mansoni, but to considerably varying degrees. Some populations even seem to be non-susceptible or very weakly susceptible. Moreover, several snail species have shown that specific populations have very variable susceptibility, depending on the parasite strain in question 2 . Within some species of Biomphalaria high variation in shell morphology and anatomy is known, which makes identification difficult. Methods for clearer characterization and identification of species would be very valuable. Morphological differentiation between species has been based mainly on characters of the shell, kidney and prostate gland; these characters are difficult for non specialists to assess. The fact that the South American species Biomphalaria glabrata (Say, 1818), which is highly susceptible to S. mansoni and much used for laboratory work, has been reported to occur in the Nile Delta in Egypt 3 , has highlighted the need to develop good methods for differentiation between species. Random Amplified Polymorphic DNA (RAPD) has previously been shown to be valuable in characterization of pulmonate species 4,5 and populations within a species 6,7 . In the present study RAPD was utilised to differentiate species and populations of Biomphalaria from Egypt and other countries. The snail material (Table 1) comprised laboratory-bred specimens of B. alexandrina (Ehrenberg, 1831), B. glabrata (Say, 1818), B. pfeifferi (Krauss, 1848) and B. sudanica (Martens, 1870), and field-collected snails from 3 populations in the Nile Delta. According to preliminary examination of morphological characters of the shell and anatomy (kidney and prostate lobes), the Nile Delta populations were provisionally identified as B. glabrata (taxon n1), B. alexandrina (taxon n2) and an indeterminate form (taxon n3). The material from the field included in the study (Table 1) was preserved in 70% ethyl alcohol. Snails from the laboratory stocks were likewise killed in alcohol just before the preparation for analysis. DNA from the snail foot was extracted by the phenol/chloroform extraction method and amplified using 40 RAPD 10-mer primers of the A and the G series from Operon Technologies, Atlanta, USA. Of the several primers that showed differences between species, OPG 19 and OPA 18 showed the clearest differences and those results are presented here. Staining was performed as an ethidium bromide staining and the gels were photographed under ultraviolet light. The figures presented are visually the best ones of a series of repeated experiments giving the same result (banding pattern). The primer OPG 19 showed differences between all 4 species examined (Fig. 1) and especially between B. glabrata and B. alexandrina. B. sudanica (s) appears more polymorphic, but differs from B. glabrata and B. alexandrina. B. pfeifferi shows characteristic but less strong bands; though only two specimens are involved in this analysis, previous analysis has shown that B. pfeifferi is well characterised by this primer 8