Effect of two-month interval mass chemotherapy on the reinfection of Ascaris lumbricoides in Korea

Atrial to control reinfection cycle of Ascaris lumbricoides was made in a rural village in Korea by blocking the process of new egg production. Chemotherapy with pyrantel pamoate was repeated bimonthly in three hamlet groups, each consisted of 105~149 inhabitants of whole age group. In one hamlet (2.5 mg/kg dose) blanket mass treatment was repeated for 18 times from June 1977 to May 1980. In other two, 5.0 mg and 10.0 mg/kg dose groups, treatment was undertaken for 10 times from June 1977 until December 1987 and later reinfection patten was observed. Follow-up examination was made by whole-day stool collection for 2 days from each case after every treatment. The samples were examined both for eggs and worms, adult and immature young, of A. lumbricoides. The results obtained are summarized as follows: 1. The pre-treatment egg positive rate in Group A, B and C was 48.1, 45.3 an 37.8% respectively. 2. The lowest dose of pyrantel pamoate, 2.5 mg/kg was equally effective as higher doses in case of repeated use for reinfection control. 3. Among 4,311 pyrantel treatments, only 8 cases complained of side effects such as abdominal pain and diarrhea. 4. When the blanket mass chemotherapy was continued 18 times in Group A, all of the examined inhabitants were free from reinfection and egg production from 28th month (the 15th treatment) until the end of study period, for 8 months. 5. When the mass chemotherapy was stopped after 10 times, the egg positive rate returned gradually up to half of pre-treatment level within one year. 6. From the analysis of total 124 positive cases during the course of follow-up, it was revealed that the mass chemotherapy with 2-month interval was successful for the suppression of fertilized egg production. However, social factors such as infected immigrants or absentees were inevitably encountered and involved in the fertilized egg production. Summarizing the results, at least 28-30 months were needed to eradicate A. lumbricoides in the subjected area of Korea, by repeated blanket mass treatment bimonthly with a quarter dose of pyrantel pamoate. Furthermore, to lessen the social factors as a source of later reinfetion, the project area of control programme should be extended as wide as possible.