Abstract
This is a survey of the incidence of hookworm infection and a study of infection process in a rural village named. Haebaru, Okinawa Prefecture. Mass treatment of hookworm carriers was repeated for six years from 1963 to 1968, and its effect on the whole incidence and new and re-infections was studied extensively. In addition, the biological behaviour and resistance of N. americanus and A. duodenale have been investigated. Incidence of hookworm infection in this community was 32.4%, mostly caused by N. americanus. The incidence was highest among the farmers as judged by the age and distribution of infected persons in regard to farming, indicating the correlation between the length of farm work hours and the incidence of hookworm infection. The infection took place mainly in the fields where sugar cane, white gourd melon and Chinese cabbage were planted, according to the investigation of plant distribution, mode of fertilization and the incidence of hookworm dermatitis. Infection was not affected by seasonal difference. The factors contributing to the high incidence of hookworm infection in this area must be the warm humid climate, the unique agricultural pattern of producing sugar cane and other vegetables, and improper disposal of the night soil. Six years of mass treatment of hookworm infection resulted in the decrease of the infection rate, markedly among the aged and children, but insignificantly among the farmers who showed frequent new and re-infections. A. duodenale infection decreased markedly, far more than N. americanus infection. The incidence of new infection was highest among the adult females, mostly infected by N. americanus. The survival time of hookworms in distilled water was longer at low temperature and shorter at high temperature, and the hatching rate was highest at 27 C. A. duodenale survived longer than N. americanus at high as well as low temperature. Toxicity of fertilizers tested was strongest with calcium cyanamide, followed by ammonium sulfate, superphosphate, and potassium chloride. They affected N. americanus much more than A. duodenale. Three tested pesticides, Dieldrin, Sumithion and Malathion demonstrated weak toxicity on hookworms. Hookworms, N. americanus in particular, proved little resistance to nitric acid, phosphoric acid and lactic acid in the order listed, and also to alkali such as sodium hydroxide, ammonium hydroxide and sodium carbonate. The larvae were vulnerable to sodium nitrite, carbon disulfide and distilled water, showing no difference due to pH.
