Abstract
BACKGROUND: Schistosoma japonicum (S. japonicum) is an important zoonotic parasite that is prevalent in China and parts of Southeast Asia. Water buffaloes are an important reservoir and the main transmission sources of S. japonicum. However, self-curing and resistance to re-infection have been observed in water buffaloes. RESULTS: In this study, we compared the morphometry and differences in transcriptional expression of adult S. japonicum worms recovered from primary-infected and re-infected water buffaloes using Illumina RNA-sequencing (RNA-Seq) technology. Results of morphometry analysis revealed that adult S. japonicum worms recovered from re-infected water buffaloes were runtish with smaller organs. The ventral length of male worms was shorter in re-infected buffaloes (328 ± 13 vs 273 ± 8 µm, P < 0.05), and in female worms the oral sucker length (44 ± 3 vs 33 ± 5 µm, P < 0.05), ovary length (578 ± 23 vs 297 ± 27 µm, P < 0.05) and width (150 ± 8 vs 104 ± 9 µm, P < 0.05) were shorter, with fewer eggs in the uteri (41 ± 2 vs 12 ± 1, P < 0.05). Of 13,605 identified genes, 112 were differentially expressed, including 51 upregulated and 61 downregulated genes, in worms from re-infected compared with primary-infected water buffaloes. Gene ontology (GO) enrichment analysis revealed that GO terms such as "oxidation-reduction process", "calcium-dependent phospholipid binding", "lipid binding" and "calcium ion binding" were significantly enriched in downregulated genes, whereas GO terms related to metabolism and biosynthesis were significantly enriched in upregulated genes. The results revealed that the downregulation of some important genes might contribute to a reduction in worm numbers and maldevelopment of surviving worms in re-infected water buffaloes. Furthermore, upregulation of genes related to metabolic processes and biosynthesis might be a compensatory mechanism of worms in disadvantageous environments. CONCLUSIONS: To our knowledge, our results present the first large-scale transcriptional expression study identifying the differences between adult S. japonicum worms from primary-infected and re-infected water buffaloes, and particularly emphasize differential expression that may affect the survival and growth of worms in re-infected water buffalo. This will provide new insight into screening for anti-schistosome targets and vaccine candidates.