title: Comparative Phylogenetic Studies on Schistosoma japonicum and Its Snail Intermediate Host Oncomelania hupensis: Origins, Dispersal and Coevolution.
abstract: BACKGROUND
  Schistosoma japonicum causes major public health problems in China and the Philippines; this parasite, which is transmitted by freshwater snails of the species Oncomelania hupensis, causes the disease intestinal schistosomiasis in humans and cattle. Researchers working on Schistosoma in Africa have described the relationship between the parasites and their snail intermediate hosts as coevolved or even as an evolutionary arms race. In the present study this hypothesis of coevolution is evaluated for S. japonicum and O. hupensis. The origins and radiation of the snails and the parasite across China, and the taxonomic validity of the sub-species of O. hupensis, are also assessed.
  
  
  RESULTS
  The findings provide no evidence for coevolution between S. japonicum and O. hupensis, and the phylogeographical analysis suggests a heterochronous radiation of the parasites and snails in response to different palaeogeographical and climatic triggers. The results are consistent with a hypothesis of East to West colonisation of China by Oncomelania with a re-invasion of Japan by O. hupensis from China. The Taiwan population of S. japonicum appears to be recently established in comparison with mainland Chinese populations.
  
  
  CONCLUSIONS
  The snail and parasite populations of the western mountain region of China (Yunnan and Sichuan) appear to have been isolated from Southeast Asian populations since the Pleistocene; this has implications for road and rail links being constructed in the region, which will breach biogeographical barriers between China and Southeast Asia. The results also have implications for the spread of S. japonicum. In the absence of coevolution, the parasite may more readily colonise new snail populations to which it is not locally adapted, or even new intermediate host species; this can facilitate its dispersal into new areas. Additional work is required to assess further the risk of spread of S. japonicum.
authors.affiliation: State Key Laboratory of Biotherapy, West China Hospital, West China Medical School, Sichuan University, Chengdu, People's Republic of China; Department of Life Sciences, The Natural History Museum, London, United Kingdom.
authors.forename: Stephen W
authors.initials: SW
authors.lastname: Attwood
authors.affiliation: School of Earth Sciences, The Ohio State University, Columbus, Ohio, United States of America.
authors.forename: Motomu
authors.initials: M
authors.lastname: Ibaraki
authors.affiliation: Department of Environmental Parasitology, Tokyo Medical and Dental University, Tokyo, Japan.
authors.forename: Yasuhide
authors.initials: Y
authors.lastname: Saitoh
authors.affiliation: Laboratory of Parasitology, School of Veterinary Medicine, Azabu University, Sagamihara, Japan; Department of Medical Entomology, National Institute of Infectious Diseases, Tokyo, Japan.
authors.forename: Naoko
authors.initials: N
authors.lastname: Nihei
authors.affiliation: Bioinformatics and Genomics, University of North Carolina at Charlotte, Charlotte, North Carolina, United States of America.
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Janies
mesh_terms: D000818:Animals; D005075:Biological Evolution; D002681:China; D006801:Humans; D007564:Japan; D008969:Molecular Sequence Data; D010802:Phylogeny; D058974:Phylogeography; D012549:Schistosoma japonicum / Q000145:classification / Q000235:genetics / Q000302:isolation & purification* / Q000502:physiology; D012552:Schistosomiasis / Q000469:parasitology* / Q000635:transmission; D012908:Snails / Q000145:classification / Q000235:genetics / Q000469:parasitology*