토양조성이 회충 및 십이지장충의 만연에 미치는 역학적연구

Abstract

[한글]

[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)

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(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)

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*…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.

Hilly

Mountainous

Parasite +-------------+--------------+---------------