Electrophoretically-detected allozyme variation is described in strains of Schistosoma japonicum (4 Philippine strains), S. mekongi (Laos), and an undescribed anthropophilic S. japonicum-like schistosome from Peninsular Malaysia. Result, together with those reported previously for 8 other strains (S. japonicum, China, Formosa, Japan, Philippines; S. mekongi, 2 substrains; Malaysian schistosome, 2 strains) permit a composite genetic characterization of 15 strains of Asian schistosomes at 9-18 presumptive loci. The proportion of polymorphic loci (P) and the mean heterozygosity per locus (H) were zero in all strains. Although this was expected for strains that had been in laboratory culture for up to 50 years, we expected to detect variation in strains based on 10-50 recently field-collected infected snails. We expected S. japonicum to be as variable as S. mansoni (P = 0.13 (0-0.33), H = 0.04, 18 loci, 22 strains) as it is believed to reproduce sexually, has an evolutionary history of several million years, inhabits a wide geographic range, coevolved with a genetically variable intermediate snail host, and has a diversity of mammalian hosts. No differences were detected between the 5 S. japonicum strains from Leyte and Luzon (Philippines), between the 3 S. mekongi strains, or between the 3 Malaysian schistosome strains; these groups and the remaining S. japonicum strains representing Mindoro (Philippines), China, Formosa, and Japan each have distinctive multilocus electromorphic patterns. Nei's genetic distances (D) were calculated to estimate interstrain and interspecific divergence. Interstrain genetic distances in S. japonicum averaged greater than 0.3; much higher than those reported previously for S. mansoni (D = 0.06, D(max) = 0.24). S. japonicum (Mindoro) was moderately differentiated from the Leyte-Luzon strains (D = 0.29, 12 loci). Estimates of the S. japonicum China-Philippine distance (D greater than 0.4, 11 loci) are high for conspecific populations and further studies of the still poorly characterized Chinese parasite may reveal that these are, in fact, separate species. S. japonicum is shown to be only distantly related to S. mekongi and the Malaysian schistosome (D greater than 1); the latter is closely related to, but genetically quite distinct from, S. mekongi (D = 0.61 +/- 0.275, 11 loci) and warrants recognition as a new species. The medical significance of the isogenic nature of the Asian schistosome strains and their evolutionary divergence are discussed.
Recognition sites for nine different restriction endonucleases were mapped on rDNA genes of fasciolid species. Southern blots of digested DNA from individual worms were probed sequentially with three different probes derived from rDNA of Schistosoma mansoni and known to span between them the entire rDNA repeat unit in that species. Eighteen recognition sites were mapped for Fasciola hepatica, and seventeen for Fasciola gigantica and Fascioloides magna. Each fasciolid species had no more than two unique recognition sites, the remainder being common to one or both of the other two species. No intraspecific variation in restriction sites was noted in F. hepatica (individuals from 11 samples studied; hosts were sheep, cattle and laboratory animals; geographical origins. Australia, New Zealand, Mexico, U.K., Hungary and Spain), or in F. gigantica (two samples; Indonesia and Malaysia). Only one sample of F. magna was available. One specimen of Fasciola sp. from Japan (specific identity regarded in the literature as uncertain) yielded a restriction map identical to that of F. gigantica. Almost all recognition sites occurred in or near the putative rRNA coding regions. The non-transcribed spacer region had few or no cut sites despite the fact that this region is up to about one half of the entire repeat unit in length. Length heterogeneity was noted in the non-transcribed spacer, even within individual worms.
The intestinal tract of schistosomes opens at the mouth and leads into the foregut or oesophageal region that is lined with syncytium continuous with the apical cytoplasm of the tegument. The oesophagus is surrounded by a specialised gland, the oesophageal gland. This gland releases materials into the lumen of the oesophagus and the region is thought to initiate the lysis of erythrocytes and neutralisation of immune effectors of the host. The oesophageal region is present in the early invasive schistosomulum, a stage potentially targetable by anti-schistosome vaccines. We used a 44k oligonucleotide microarray to identify highly up-regulated genes in microdissected frozen sections of the oesophageal gland of male worms of S. mansoni. We show that 122 genes were up-regulated 2-fold or higher in the oesophageal gland compared with a whole male worm tissue control. The enriched genes included several associated with lipid metabolism and transmembrane transport as well as some micro-exon genes. Since the oesophageal gland is important in the initiation of digestion and the fact that it develops early after invasion of the mammalian host, further study of selected highly up-regulated functionally important genes in this tissue may reveal new anti-schistosome intervention targets for schistosomiasis control.
The present study describes a real-time PCR approach with high resolution melting-curve (HRM) assay developed for the detection and differentiation of Schistosoma mansoni and S. haematobium in fecal and urine samples collected from rural Yemen. The samples were screened by microscopy and PCR for the Schistosoma species infection. A pair of degenerate primers were designed targeting partial regions in the cytochrome oxidase subunit I (cox1) gene of S. mansoni and S. haematobium using real-time PCR-HRM assay. The overall prevalence of schistosomiasis was 31.8%; 23.8% of the participants were infected with S. haematobium and 9.3% were infected with S. mansoni. With regards to the intensity of infections, 22.1% and 77.9% of S. haematobium infections were of heavy and light intensities, respectively. Likewise, 8.1%, 40.5% and 51.4% of S. mansoni infections were of heavy, moderate and light intensities, respectively. The melting points were distinctive for S. mansoni and S. haematobium, categorized by peaks of 76.49 ± 0.25 °C and 75.43 ± 0.26 °C, respectively. HRM analysis showed high detection capability through the amplification of Schistosoma DNA with as low as 0.0001 ng/µL. Significant negative correlations were reported between the real-time PCR-HRM cycle threshold (Ct) values and microscopic egg counts for both S. mansoni in stool and S. haematobium in urine (p < 0.01). In conclusion, this closed-tube HRM protocol provides a potentially powerful screening molecular tool for the detection of S. mansoni and S. haematobium. It is a simple, rapid, accurate, and cost-effective method. Hence, this method is a good alternative approach to probe-based PCR assays.
Complete sequences were obtained for the coding portions of the mitochondrial (mt) genomes of Schistosoma mansoni (NMRI strain, Puerto Rico; 14 415 bp), S. japonicum (Anhui strain, China; 14 085 bp) and S. mekongi (Khong Island, Laos; 14 072 bp). Each comprises 36 genes: 12 protein-encoding genes (cox1-3, nad1-6, nad4L, atp6 and cob); two ribosomal RNAs, rrnL (large subunit rRNA or 16S) and rrnS (small subunit rRNA or 12S); as well as 22 transfer RNA (tRNA) genes. The atp8 gene is absent. A large segment (9.6 kb) of the coding region (comprising 14 tRNAs, eight complete and two incomplete protein-encoding genes) for S. malayensis (Baling, Malaysian Peninsula) was also obtained. Each genome also possesses a long non-coding region that is divided into two parts (a small and a large non-coding region, the latter not fully sequenced in any species) by one or more tRNAs. The protein-encoding genes are similar in size, composition and codon usage in all species except for cox1 in S. mansoni (609 aa) and cox2 in S. mekongi (219 aa), both of which are longer than homologues in other species. An unexpected finding in all the Schistosoma species was the presence of a leucine zipper motif in the nad4L gene. The gene order in S. mansoni is strikingly different from that seen in the S. japonicum group and other flatworms. There is a high level of identity (87-94% at both the nucleotide and amino acid levels) for all protein-encoding genes of S. mekongi and S. malayensis. The identity between genes of these two species and those of S. japonicum is less (56-83% for amino acids and 73-79% for nucleotides). The identity between the genes of S. mansoni and the Asian schistosomes is far less (33-66% for amino acids and 54-68% for nucleotides), an observation consistent with the known phylogenetic distance between S. mansoni and the other species.