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토양조성이 회충 및 십이지장충의 만연에 미치는 역학적연구

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 Epidemiological studies on the relationship between soil composition and the infestation of ascaris and hookworm 
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[영문] Under certain circumstances the ova of ascaris and hookworm which are discharged from the human body develop an infective form in soil. Thus soil serves as an important medium for the spread of human parasites. It may be conjected that the development of parasite eggs is not only strongly influenced by the sunrays, temperature, moisture, wind and rainfall etc., but also character of the soil-geological composition, acidity and other factors. There have been many studies of the interrelationship between parasite infestation and natural environment. Beaver(1952) reported on the effects of soil composition on development of infections of ascaris and hookworm, although Mihara(1960) found no specific relationship between these factors. Unfortunately, ascaris and hookworm are widely prevalent among Koreans and this infestation has become a most serious public health problem in Korea. No epidemiological study on the relationship between soil character and parasite infestation has been carried on in this country. In this study, the author attempted to clearify the relationship between soil composition and ascaris and hookworm infestation, in an area in which the natural living environment was similar. A summary of the results of this study is as follows. Materials nod Methods Four geographic areas were selected; mountainous, hilly, plain fields, and islands, all located in Chonpuk province. The Socio-economic and control environment and customs were similar in all four areas. 3 villages were chosen from each area. In each village survey was made emphasizing 3 points; a. Examination of soil composition; 10 samples of dooryard soil were taken from each village. b. Examination of soil contaminated by ascaris ova and hookworm larvae: 10 soil samples of inner garden soil around the manure heap were taken from 5 houses where families infested with ascaris and hookworm lived. c. Examination of the incidence of parasites and the number of worms; about 120 people in each village were examined. In order to supplement the above findings, the following experiments were made. a. Water retention power test in various types of artificial soil. b. Survival test of bookworm eggs in various types of artificial soil. c. Measurement of the NaCl content in soil from the islands. d. Tests of survival hookworm eggs and larvae at various concentrations of NaCl. e. Tests on survival of ascaris and hookworm eggs in soils in which the pH was varied. Results 1. The results of studies in 12 villages in 4 different geographic areas are as follows (Table 1, 2). (Table 1) Soil composition of earth area Area Item Mountainous Hilly Plain fields Island Soil composition (10 samples at each village) Sand(%) Average(range) 74(66-82) 43(40-47) 12( 9-14) 53(41-59) Silt(%) 22(14-30) 46(44-48) 81(79-84) 30(17-49) Clay(%) 4( 3-5 ) 11( 5-16) 7( 5-8 ) 17(10-24) ------------------------------------------------------------------------------- (Table 2) The incidence of ascafis and hookworm in the three areas --------------------+-------------+--------------------------------------------
Area Item
Island --------------------+-------------+-------------+--------------+--------------- Incidence* Ascaris(%) 44.5 44.1 81.5 (39.2-50.2) (37.1-50.0) (73.4-86.8) Hookworm(%) 44.4 23.1 18.5 (13.5-46.0) (17.1-28.0) (14.4-22.4) AS/HW ratio 1.0 1.9 4.5 (0.8-3.1) (1.4-2.7) (3.8-5.3) E.P.G**/feces/capita Ascaris 7,532 9,513 14,649 (6,410-9,034) (7,600-12,314) (11,744-18,718) Hookworm 1,740 877 667 (786-1,741) (800-933) (442-821) Worm burden esti- Ascaris 7 10 15 mate/ capita (6-9) (8-12) (12-19) Hookworm 56 35 25 (31-69) (32-36) (16-32) ------------------------------------------------------------------------------- *…Average 120 exminations at each area. **…Egg per gram In the above findings, the ratio of ascaris to hookworm infestation was almost same (1.0:1.0) in the mountainous area where the soil was over 70% sand. However, in the hilly region where the soil was 40% sand the ratio was 1.9:1.0, and in plain fields with only 12% sand the ratio was 4.5:1.0. The prevalence of hookworm paralleled the percentage of sand in the soil. Ascariasis, on the contrary was the most frequent in the plain field soil where the percentage of sand was low. The incidence of ascaris infestation showed no significant changes in the areas containing over 40% sand, but hookworm had its peak concentration in the area of the highest sand percentage (60-70%). In islands, although hookworm were found only one case (2.5%) out of U examinations, there was a high prevalence of ascaris(82.3%). Supplementary experiments demonstrated that salt in the island soil inhibited the development of bookworm ova and larvae. Ⅱ. Experiment on the survival of ascaris and hookworm ova in soils of different composition. a. Experiments on soil of different composition (artificial soil): In soil which contained no sand, the hookworm ova were destroyed within a week. The survival rate increased as the percentage of sand content increased. Even in dry sandy soil, the hookworm ova survived about two weeks. 80% of ascaris eggs developed to infective form in soil without regard to the sand content, and in drought conditions they survived for three weeks. But in soil holding 100% of sand or clay, the ova developed and died rapidly. b. Experiments on the NaCl content of island soil and the survival of hookworm ova: The island soil contained NaCl at the rate of 0.13-1.00 gm/dl and none of the soils in islands contained 3.00gm/dl as sea water. The island soil inhibited the growth of hookworm eggs, but had no influence on the development of ascaris eggs. Hookworm ova did not develop to the second stage larvae in soil which contained over 1.0% Nacl. Conclusions 1. The hookworm infestation rate in villages of different soil composition was closely related to the proportion of sand in the soil. 2. The rate of soil contamination with hookworm larvae was high in the mountainous area, while, on the contrary, ascaris ova were the most frequent in the plain field area. 3. Among the island villagers, only one case of hookworm infection was found in 86 examinations, while the ascaris infection rate was 82.3%. The salty soil of the islands inhibited the development of hookworm eggs, but there was no similar effect on the growth of ascaris eggs. 4. The hydrogen ion concentration rate of soil (pH 5.0-7.0) showed no influence on the development of the ova of ascaris or hookworm. 5. In epidemiological studies of sail composition and the incidence of ascaris and hookworm infestation a close interrelationship was demonstrated.
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2. Thesis / Dissertation (학위논문) > 1. College of Medicine (의과대학) > Ph.D. (박사)
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