在日本血吸虫病的早期研究中,曾一度认为本病没有中间宿主,是由虫卵孵化成蚴虫后直接感染的。之后的研究才发现本病必须有中间宿主这一环节,即保虫宿主(病人病畜和野生动物)——中间宿主——保虫宿主,中间宿主就是钉螺。虽然存在着有螺无病人或有病人无螺的现象,前者可能与传染源及自然条件有关,后者的病人则是自疫区迁徙而来。本病的传染源的定义:感染了血吸虫病并能排出血吸虫虫卵的人、家畜及野生动物。这一定义 In the early study of schistosomiasis japonica, once thought there was no intermediate host disease, is directly infected by eggs hatch into a larvae. After the study found that the disease must have an intermediate host of this link, that is, host insecticide (patient sick animals and wildlife) - intermediate host - host insecticide, the intermediate host is snail. Although there are spiro-free patients or patients with non-snail phenomenon, the former may be related to sources of infection and natural conditions, while the latter is from the epidemic area of ​​patients migrate from. The source of this disease is defined as: people infected with schistosomiasis and can discharge schistosome eggs, livestock and wildlife. This definition