My epidemiological studies on ascaris and hook-worm infection in heavy snowing area, Tamugiyama, Chida, Kamioguni and other villages in Niigata Prefecture, conducted from 1951 to 1955, have revealed the following facts.
1. Incidence of ascaris and hook-worm infection in heavy snowing area did not differ much from the one in non snowing area.
2. Epidemiological studies on ascaris.
a. The average rate of ascaris infection per year in Tamugiyama village was 23%, during the 3 years from 1952 to 1955.
b. The average rate of ascaris infection per year among schoolchildren in Tamugiyama and Kamioguni villages was 60.4% from 1951 to 1952.
c. The seasonal fluctuation of ascaris infection indicated higher ratesfrom harvest time to winter (from October to January), then became lower.
d. By the mass treatment conducted in every winter, the incidence of ascaris infection gradually decreased from 54% in 1952 to 35% in 1955.
3. Epidemiological studies on hook-worms.
a. Both species of hook-worms were found; however, Ancylostoma duodenale Dubini predominated in Niigata Prefecture, especially in snowy areas.
b. By the mass treatment conducted in every winter, the incidence of hook-worm infection decreased rapidly, from 52% in 1952 to 21% in 1955.
4. By these various investigations, I found out that the speed of ascaris and hook-worminfection (how soon reinfection occurred) was lower in heavy snowing area than those in non snowing area.