Epidemiology and control of ascariasis in Korea

In view of the epidemiology and control strategy, ascariasis was reviewed with special reference to the data obtained for the past years in Korea. The range of length and prepatent period of A. lumbricoides to become fertile were 12.5-13.5 cm and 1.8-2.1 months for females, and 10.5-11.5 cm and 2.1-2.5 months for males, respectively. In the female worm burden 1 per case, the egglaying capacity steadily increased from 12.6 cm of their length up to 25.0 cm and then decreased significantly after their growth to 27.5 cm. Analysed the egg discharging pattern, it was turned out that the cases with six or more worms have no probability to be false negative or unfertilized ova passer, and 52% of all false negatives were found infected only with male(s). The sex ratio was in the range of 0.74-0.82 (male/female). Basic reproductive rate was calculated in the range of 1.16-2.11 in rural areas, but it was approaching nearly to the 'break point' in some areas. It was observed that the 'U-rate' was increased from 19.4% (1973) to 61.1% (1989) for the past seventeen years. According to the survey in 6 rural areas, the average worm burden was 2.2 per population and 4.5 per infected. The frequency distribution pattern of A. lumbricoides per person in a rural community was well fitted to the negative binomial distribution. Seasonal fluctuation was shown in two, smaller and larger, peaks. The annual prevalence in student group was initially 55.4% in 1969, but decreased to 0.3% in 1989, and it is evident that the decrease has been greatly owing to the national control project. It was proved that the efficacy of a quarter dose of pyrantel pamoate used in long term control programme was almost equal to that of conventional dose (10 mg/kg). The comparatie efficacy of various interval mass chemotherapy schemes was evaluated through 2 year observations, and it was confirmed that at least biannual mass chemotherapy is necessitated to expect gradual lowering of reinfection. In the case of blanket treatments with 2-month interval in a village, all of inhabitants have been free from reinfection for the period of 28 months after the initial treatment. It was fully recognized that without specific legislation and organization supported by the government, the national mass control programme has almost no chance of success, especially in developing countries.(ABSTRACT TRUNCATED AT 400 WORDS)