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Epidemiology of Amebiasis: Possible Influence of Water Supply, Coincident with Diverse Features of Terrain, on the Occurrence of Intestinal Protozoa

The observations presented indicate that the incidence of protozoan infections was lower on the floor of the Kofu Valley, Yamanashi Prefecture, Japan, where drinking water was obtainable from open wells, than in secondary valleys of surrounding mountains where the primary source of water was either a river or an irrigation stream. For Endamoeba histolytica the incidence tended to increase from upper to lower levels of the valley, in agreement with an expected increase in fecal pollution. Fluctuations in the incidence of E. coli and E. nana which were irrespective of valley levels, and a disproportionate increase in the rate of E. histolytica in the hill communities prompt the speculation that the several modes of protozoan transmission may not be equally effective for E. histolytica and the other amebas. Since cyst drying has been shown to be less damaging to E. coli and E. histolytica, the latter may be more dependent on water transmission. Although other factors such as direct and food handler transmission and flies may have contributed to the increased incidence of protozoa in hill villages, it is believed that water was the major factor of difference.

¹ Present address: AMSGS, Walter Reed Army Medical Center, Washington 12, D. C.

² APO 500, c/o Postmaster San Francisco, California.