An Observation on the Reinfection Pattern of Metagonimus yokogawai among Inhabitants in Tamjin River Basin

Abstract

The reinfection pattern of Metagonimus yokogawai was studied at Tamjin river basin, one of its well-known endemic areas in Korea. Stool specimens of a total of 230 inhabitants were examined and 68 (with high egg counts) out of 99 positive cases were treated with 10 mg/kg single dose of praziquantel in January 1984. Follow-up stool examinations were performed every 3 months for a period of one year. The results were as follows: 1. The pretreatment egg positive rate was 43.0% and their average EPG 1,560 (range; 020,800). The rate in male inhabitants was higher (46.9%) than in females (39.3%), and age groups older than 21 (male) and 31 (female) years revealed over 70% and 60% positive rates, respectively. 2. After the treatment, the rate in whole subjected people decreased to 16.7% in April, but increased thereafter to 24.5% in July, 24.7% in October and 32.1% in January ('85). The average EPGs in April and July were remarkably lower than before treatment, but it returned back to or exceeded the pretreatment level in October and January('85). 3. Up to half (10.6-54.3%) of the treated inhabitants appeared reinfected during the follow-up period, while only a few proportion (3.4-7.9%) of uninfected cases turned to egg positive. Approximately a half of infected but untreated cases turned to egg negative, which suggests spontaneous cure. From the results, it is inferred that new infection by M. yokogawai occurs mainly in the season from mid-summer (July) to late autumn (November or so), especially to people who like to eat raw sweetfish.