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Korean J Parasitol > Volume 21(2):1983 > Article

Original Article
Korean J Parasitol. 1983 Dec;21(2):135-141. English.
Published online Mar 20, 1994.  http://dx.doi.org/10.3347/kjp.1983.21.2.135
Copyright © 1983 by The Korean Society for Parasitology
Epidemiological studies on Ascaris lumbricoides reinfection in rural communities in Korea 1. The relationship between prevalence and monthly reinfection rate
Jong-Yil Chai
Department of Parasitology and Institute of Endemic Diseases, College of Medicine, Seoul National University, Korea.

The epidemiological relationship between the current prevalence and monthly reinfection rate of Ascaris lumbricoides was observed in rural communities in Korea by measns of blanket mass chemotherapy and worm collection for measurement of the prevalence and reinfection rates. During the period from 1975 to 1980, a total of 4,466 inhabitants in 10 different localities were treated with 10 mg/kg of pyrantel pamoate and 2 days' whole stools were collected from 2,547 inhabitants. The stools were examined for the presence of expelled adult and/or young worms, which represent the prevalence and reinfection rates for past 2 months respectively. After then, the obtained rates were correlated each other applying the time-prevalence curve proposed by Hayashi.

It was observed that the prevalence (overall worm positive rate) and worm burden per individual ranged by areas from 13.6 to 72.3% and 1.4-10.2 respectively. The calculated monthly reinfection rates (X) (from young worm positive rates) according to areas were in the range, 2.6~16.2%, and clearly correlated with the current prevalence (Y) under the equation, Y=1-(1-X)7.2 where 7.2 is time in month. The equation means that after one time mass chemotherapy the period needed to attain equilibrium of prevalence again would be about 7~8 months. And it is inferred that the majority of reinfected worms in human host turn over every 7~8 months.


Fig. 1
Regression curve, Y=1-(1-X)N, between prevalence (Y) and monthly reinfection rate (X) of A. lumbricoides, where 'N' is the constant value (6, 7.2 or 9) of time in month.

Fig. 2
Time-prevalence curves when monthly reinfection rates are variable. The equation is Y=1-(1-X)N, where 'Y' is the prevalence and 'N' is time in month. (A) Continuous elevation of prevalence so far as the equation is concerned, (B) Suggested feature of maintenance of equilibrium in prevalence after 7~8 months. (a) when monthly reinfection rate (X) is 20%, (b) X=15%, (c) X=10%, (d) X=5% and (e) X=2%.


Table 1
The results of worm collection study of A. lumbricoides in various areas, Korea (1975~'80)

Table 2
Young worm positive rate and monthly reinfection rate of A. lumbricoides

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