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From 2007–2014, 19,360 freshwater snails from the Terai and Hilly regions of Nepal were screened for cercariae of mammalian schistosomes. Based on analysis of mitochondrial cytochrome oxidase I, 12S, 16S and 28S sequences (3,675 bp) of the cercariae recovered, we provide, to our knowledge, the first report of the Schistosoma indicum species group in Nepal. Five samples of Schistosoma nasale , nine of Schistosoma spindale and 17 of Schistosoma sp. were recovered, all from the snail Indoplanorbis exustus . The last-mentioned lineage failed to group in any of our analyses with S. nasale , S. spindale or S. indicum . It diverged in cox 1 sequence from them by 16%, 13% and 13%, respectively, levels of difference comparable to well-studied species pairs of Schistosoma . Analysis of cox 1, 16S and internal transcribed spacer 1 sequences (1,874 bp) for Nepalese specimens of I. exustus was also surprising in revealing the presence of four genetically distinct clades. They diverged from one another at levels comparable to those noted for species pairs in the sister genus Bulinus . There was no obvious pattern of use by Nepalese Schistosoma of the Indoplanorbis clades. We found high support for a close relationship between S. indicum and Schistosoma haematobium groups, but failed to retrieve support for a clean separation of the two, with a tendency for S. nasale to fall as the most basal representative. If this pattern holds, hypotheses for the origin of the Asian Indoplanorbis -transmitted S. indicum group from the Bulinus -transmitted S. haematobium group may require modification, including consideration of more contemporaneous origins of the two groups. The Indian subcontinent is under-studied with respect to schistosome diversity and our current knowledge of the S. indicum and I. exustus species groups is inadequate. Further study is warranted given the ability of indicum group species to cause veterinary problems and cercarial dermatitis, with a worrisome potential in the future to establish infections in humans. [ABSTRACT FROM AUTHOR]

As part of a global survey of schistosomes, a total of 16,109 freshwater snails representing 14 species were collected from lakes, ponds, rivers, rice fields and swamps mostly in the Terai region of southern Nepal. Only two snails were found to harbor avian schistosome cercariae even though Nepal is well known for its rich avian diversity. One schistosome infection was from an individual of Radix luteola and on the basis of phylogenetic analyses using 28S rDNA and cox1 sequences, grouped as a distinctive and previously unknown lineage within Trichobilharzia. This genus is the most speciose within the family Schistosomatidae. It includes 40 described species worldwide, and its members mostly infect anseriform birds (ducks) and two families of freshwater snails (Lymnaeidae and Physidae). The second schistosome cercaria was recovered from an individual of Indoplanorbis exustus that was also actively emerging a Petasiger-like echinostome cercaria. Although I. exustus is commonly infected with mammalian schistosomes of the Schistosoma indicum species group on the Indian subcontinent, this is the first specifically documented avian schistosome reported in this snail. Both cercariae reported here are among the largest of all schistosome cercariae recovered to date. The I. exustus-derived schistosome clustered most closely with Macrobilharzia macrobilharzia, although it seems to represent a distinct lineage. Specimens of Macrobilharzia have thus far not been recovered from snails, being known only as adult worms from anhingas and cormorants. This study is the first to characterize by sequence data avian schistosomes recovered from Asian freshwater habitats. This approach can help unravel the complex of cryptic species causing cercarial dermatitis here and elsewhere in the world., (Copyright © 2013 Elsevier B.V. All rights reserved.)