Affinities between Asian non-humanSchistosomaspecies, theS. indicumgroup, and the African human schistosomes

Abstract

Schistosoma species have traditionally been arranged in groups based on egg morphology, geographical origins, and the genus or family of snail intermediate host. One of these groups is the`S. indicum group' comprising species from Asia that use pulmonate snails as intermediate hosts. DNA sequences were obtained from the four members of this group (S. indicum, S. spindale, S. nasale and S. incognitum) to provide information concerning their phylogenetic relationships with other Asian and African species and species groups. The sequences came from the second internal transcribed spacer (ITS2) of the ribosomal gene repeat, part of the 28S ribosomal RNA gene (28S), and part of the mitochondrial cytochrome c oxidase subunit 1 (CO1) gene. Tree analyses using both distance and parsimony methods showed the S. indicum group not to be monophyletic. Schistosoma indicum, S. spindale and S. nasale were clustered among African schistosomes, while S. incognitum was placed as sister to the African species (using ITS2 and 28S nucleotide sequences and CO1 amino acid sequences), or as sister to all other species of Schistosoma (CO1 nucleotide sequences). Based on the present molecular data, a scenario for the evolution of the S. indicum group is discussed.

The phylogeny of the Schistosomatidae based on three genes with emphasis on the interrelationships of Schistosoma Weinland, 1858

“…Most recent studies have added gene fragments or additional taxa to particular clades within Schistosoma to test the position of individual taxa (e.g. Agatsuma et al 2001Agatsuma et al , 2002Blair et al 1997), or to examine some of the biogeographic hypotheses suggested by Snyder & Loker's (2000) scheme, e.g. Zhang et al (2001) and Attwood et al (2002 b).…”

Recent range expansion of an intermediate host for animal schistosome parasites in the Indo-Australian Archipelago: phylogeography of the freshwater gastropod Indoplanorbis exustus in South and Southeast Asia

“…Amongst the four recognised common Schistosoma species groups [3], the Schistosoma indicum species group has received less attention than its congeners since none of these species ultimately infect humans in the final stage of their life cycle [4–6]. However, it remains responsible for severe outbreaks of cattle schistosomiasis and human cercarial dermatitis in India and Southeast Asia [2, 7–12].…”

The Schistosoma indicum species group in Nepal: presence of a new lineage of schistosome and use of the Indoplanorbis exustus species complex of snail hosts

“…Although Schistosoma incognitum was formerly included in this group, it has been shown that it is a more distant relative (Agatsuma et al, 2002; Attwood et al, 2002; Morgan et al, 2003; Webster et al, 2006: Lawton et al, 2011). Among the four customarily recognized and prominent species groups, our overall knowledge of the S. indicum group lags far behind the other three.…”

“…Adult males of this species have prominent tubercles, most of which lack spines (Southgate et al, 1990). This species is known from India, Bangladesh, Myanmar and Sri Lanka (Dutt, 1967; Rollinson and Southgate, 1987; Agatsuma et al, 2002; Lockyer et al, 2003; Attwood et al, 2007). …”