Geographical factors influencing the population numbers and distribution of Oncomelania nosophora and the subsequent effect on the control of Schistosomiasis japonica in Japan

Abstract

In order to clarify the geographical factors affecting the remarkable ubiquity of schistosomiasis japonica in Japan, topographical and edaphic conditions, as well as change of agricultural landuse of the habitats of the snails were investigated.

• 1.

  1. The landforms were classified into the following three types, with reference to the topography of flood areas. They are (1) lower deltaic plains, (2) lower alluvial fans and (3) upper alluvial fans. Many of the endemic land surface are of the first types.

• 2.

  2. From the results of cultural experiments of the snails on various kinds of soils, it was realized that the soil restricted the distribution of habitats and that the soils adequate for the fecundity and breeding of snail egg were surface materials of grey, grey-brown or brown lowland soil with the texture of sandy loam or loam and with humus content of about 2.6%.

• 3.

  3. The effects of agricultural development on the decrease of schistosomiasis cases were clarified by examining changes in the land use of the Kofu Basin, the most infected area.

• 4.

  4. A medical geographical province map of the Kofu Basin was compiled by synthesis of snail distribution and its controlling factors.