A Simple Computer-Assisted Method to Identify Schistosome Cercariae

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  • Centre de Bioinformatique, Institut National de la Sante et de la Recherche Medicale Unite 263, Universite Paris, Centre de Biologie et Ecologie Tropicale, Unite de Recherches Associee au Centre National de la Recherche Scientifique (URA CNRS), Universite, Laboratoire de Parasitologie, URA CNRS, Universite de Montpellier, Paris, France
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Several methods have been suggested to identify schistosome cercariae. In the present work, a new method is proposed, based on the analysis of the distribution of sensory endings (sensillae) on the body of the cercariae, revealed by an impregnation with silver nitrate. We determined the mutual distances between the sensillae and calculated the mean values, standard deviations, coefficients of asymmetry, and of kurtosis of the distribution of these mutual distances. Applied to two species, Schistosoma mansoni from Brazil and S. intercalatum from Cameroon, these mutual distances had the same mean value and the same standard deviation but quite different coefficients of symmetry (0.34 ± 0.11 versus 0.73 ± 0.08; P < 0.0001) and of kurtosis (-0.82 ± 0.27 versus -0.58 ± 0.31; P < 0.0001). The latter two indices were therefore very effective for discriminating the two species. The present method can be applied to other species and to hybrids in the field.