Epidemiological studies of Clonorchis sinensi in the Coastal Areas of Kyungpook Korea

Abstract

In order to determine the epidemiological patterns of the liver fluke, the infection rates for Clonorchis larvae in the snails and fish hosts, and the prevalence of C. sinensis among the residents in the coastal areas of Kyungpook Province were studied from April, 1992 to September, 1993. Four snail habitats were found in the river Hyungsan and come streams. One area had snails infected with Clonorchis cercaria, but the proportion of infected snails was very low, the average rates varying from zero to 0.081 percent. Of the 19 species of fish, 3 species were infected with the encysted larvae of C. sinensis. Infection rates varied greatly by the fish species, and ranged from 6.7 percent in P. herzi to 88.9 percent in G. artomaculatus. In the intensity of infection with C. sinensis, G. atromaculatus was the most heavily infected species, the average number of cysts per gram of the fish flesh being 72.2 followed by P. herzi with 53.0 cysts. The infection rate for C. sinensis among the residents was relatively high, being found to be 5.9 percent with a prevalence of 7.0 percent in males and 5.1percent in females. the difference in the rate of infection between males and females is found to be statistically significant(t>2). For the quantitative analysis of epidemiology of C. sinensis, a special type of simple catalytic model was applied to the sex and age infection rates revealed by stool examination for Clonorchis eggs. The simple catalytic curve for males was y=0.21(1-e-0.021t), and females was y=0.19(1-e-0.013t). From these equations the force of infection of 2.1 and 1.3 effective infections giving positive stool examination per 1,000 residents annually was suggested. And the asymptote is at about 21.0 percent of males and 19.0 percent of females, the estimated values of the limit of possible positive cases in the residents. For the analysis of the age prevalence patterns of Clonorchis positives applied the two-stage catalytic model, and the equation is y=0.511(e-0.0093t-e-0.0275t). for the analysis of the 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 is y=1.07+1.50 log X. This study indicate that endemic foci of C. sinensis exist in the coastal areas of Kyungpook Province and the prevalence of the liver fluke among the residents is still high, and that the infection rates with Clonorchis larvae in the fresh-water fish and snails varied greatly by the species of fish and its habitats.