Epidemiological Studies of Clonorchis sinensis in the Vicinity of Cheongdo River, Kyungpook, Korea

Abstract

In order to determine the epidemiological pattern of the liver fluke, the infection rates and intensity for the metacercarial larvae of C. sinensis in the fish hosts, and the prevalence of the liver fluke among the residents in the vicinity of the Cheongdo River, Kyungpook Province Korea were studied from June, 1993 to September, 1994. Fourteen species of fresh-water fish caught in the river were examined for the encysted larvae of C. sinensis. Of these, 6 species were infected with the metacercariae of C. sinensis. Infection rates varied greatly by fish species and ranged from 16.7 per cent in P. herzi to 80.0 per cent in P. parva. As for the intensity of Clonorchis infection, P. parva was the most heavily infected species, with an average number varying from 8.8 to 11.0 cysts. The prevalence of C. sinensis among the residents in the vicinity of the Cheongdo River was relatively high, being found to be 21.0 per cent with an infection rate of 23.47 per cent in males and 17.86 per cent in females. The difference of infection rate between males and females is found to be statistically significant (t>2). For the analysis of age pre valence patterns of Clonorchis positives applied the two-stage catalytic model, and the equation was y=1.2(e(-0.015t)-e(-0.022t)) From this equation the force of infection was annually 15 per 1,000 susceptibles and the disappearance rate from positive to negative cases was annually 22 per 1,000 Clonorchis positive in this population. For the analysis of intensity of infection, the frequency distribution by the Clonorchis egg counts was calculated as well as the cumulative percentage to the total number of positive cases, and the regression equation was y=1.51+1.30 logX. These figures indicated that most cases of the residents with clonorchiasis were found to be lightly infected. This study indicate that endemic foci of C. sinensis exist in the vicinity of the Cheongdo River Cheongdo and the prevalence of the liver fluke among the residents is still high.