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KMID : 0379319830080010066
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Korean Journal of Rural Medicine
1983 Volume.8 No. 1 p.66 ~ p.80
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Epidemiological Studies of Clonorchiasis
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金東燦/Kim, D.C.
李溫永/李鍾秀/安壯洙/張泳美/孫盛昌/李星熙/Lee, O.Y./Lee, J.S./Ahn, J.S./Chang, Y.M/Son, S.C./Lee, S.H.
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Abstract
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As a part of the epidemiological studies of clonorchiasis in Korea, this study was conducted to evaluate the current endemicity and the natural transition of the Clonorchis infection in Goyang Gun a low endemic area in recent years, prior to the introduction of praziquantel which will eventually influence to the status of the prevalence. The data obtained in this study in 1983 were evaluated for natural transition of the infection in comparison with those obtained 16 years ago in 1967 by the author( Kim, 1974). The areas of investigation, villages and schools surveyed, methods and techniques used in this study were the same as in 1967, except for the contents of the questionnaire for raw freshwater fish consumption by the local inhabitants.
1) The current prevalence rate of Clonorchis infection among the inhabitants was 7.5 % on the average out of a total of 479 persons examined. The prevalence rate was 9.0% in the riverside area and 4.2% in the inland area. Among the schoolchildren, the prevalence rate was 1.1 % out of a total of 1,319 examined. By area, it was 1.4 % in the riverside area and 0.7% in the inland area. By sex, the prevalence rate was 13.3% in the male and 1.3% in the female in the inhabitants and no difference was seen in the schoolchildren.
2) In the natural transition of the infection, the prevalence rate in the inhabitants has decreased from 22.5 % in 1967 to 7.5 % in 1983, and in the schoolchildren, from 9.5% in 1967 to 1.1 % in 1983. The reduction rate was higher in the riverside area than in the inland area.
3) In the prevalence rate by age, 1.2% was seen in the 10 - 14 age group and gradually increased to 8.1 % in the 30 - 39 age group and reached peak 18.1 % in the 40 - 49 age group. By sex, in the male, the prevalence rates have increased to 31.9% and 33.3% in the 40-49 and 50-59 age groups, respectively and decreased thereafter. In the female, the prevalence rate less than 5 % was seen only in between the 10-14 and 30- 39 age groups.
4) In the natural transition of the prevalence rate by age, sharp decrease was seen in the male from around 50% in 1967 between 15 - 19 and 30 -39 age groups. The generation over 40s showed less decrease.
In the female, the prevalence rate has decreased from 13% in 1967 to 5 % in 1983 in the middle age groups and dropped to 0 % in the rest of the age groups.
5) The intensity of the infection among clonorchiasis cases by mean EPmg (number of eggs per mg feces) value was 1.4. In the inhabitants, the value was 2.0 in the riverside area and 0.4 in the inland area. While in the schoolchildren, the value was 0.2 in both riverside and inland areas.
6) In the transition of the intensity of the infection, EPmg among the inhabitants has decreased from 3.9 in 1967 to 2.0 in 1983 in the riverside area, and from 2.9 to 0.4 in the inland area. In the schoolchildren, the reduction was similar in both riverside and inland areas resulting from 1.0 - 1.1 in 1967 to 0.2 in 1983.
7) In the intensity of the infection by age, EPmg 3.4 was peak at the 40 -49 age group and 0.2- 1.0 was seen in the rest of the age groups. The mean value was 1.5 in the male and 0.6 in the female.
8) In the natural transition of the intensity of the infection, the EPmg has decreased from 2.7 in 1967 to 1.4 in 1983. By age, reduction was seen in all of the age groups, particularly in the young and the old age groups of 50s and over, except in the 40-49 age group in which reverse phenomenon was seen. By sex, it has decreased from 3.5 in 1967 to 1.5 in 1983 in the male and from 1.0 to 0.6 in the female.
9) In the distribution of the clonorchiasis cases by the range of EPmg value, 70.3% of the cases were placed in the range of 0.1-0.9 as the most and 16.2% in 1.0-4.9 as the next. With such figures, those included in the range less than 0.9 as light infection were 78.4% and under 5.0-9.9 up to moderate infection 99.3% of the cases were covered. The cases were distributed up to 20.0-39.9 in the male and to 1.0 - 4.9, in the female.
10) In the transition of the distribution of the clonorchiasis cases by EPmg, the highest intensity reached up to 60.0 -79.9 in 1967 and to 20.0 - 39.9 in 1983. In the range of light infection, under 0.1-0.9, the distribution in rate was 64.5% in 1967 and 78.4% in 1983. Up to the range of moderate infection, under 5.0-9.9, 91.7% in 1967 and 97.3 % in 1983 were seen respectively.
11) In a survey for raw freshwater fish consumption among the local inhabitants,78.3 % of the clonorchiasis cases interviewed admitted their experience of the raw consumption. However, those who practiced in the past two years were 34.8%. 55.6% of those who have such experience in the past professed that they did not practice raw freshwater fish consumption in the past two years.
12) The major cause of the reduction of the raw freshwater fish consumption among the inhabitants were the wide spread water pollution in the locality. The most common reason professed for stopping raw freshwater fish consumption among the inhabitants was the risk of the fluke infection.
13) In animal survey, 3.1 % of dogs were found infected with Clonorchis, decreasing from 21.6% in 1967.
14) The distribution of the first intermediate host, Parafossarulus manchouricus has greatly diminished in this locality and found only in two localized ponds. No Clonorchis infection was found from the snails examined.
15) The second intermediate freshwater fish host has been further limited by extended water pollution. No susceptible fish host could be examined.
16) In conclusion, the endemicity of Clonorchis infection in Goyang Gun, low endemic area, has significantly decreased during the past 16 years. The major cause of the regressive transition of the infection was the water pollution of the freshwater system of this locality. This has upset the ecosystems of the intermediate host of Clonorchis sinensis in many areas of waterbodies and further discouraged to a significant extent the local inhabitants from raw freshwater fish consumption.
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