International Collaborative Studies on the Control of Soil-Transmitted Helminthiases and Schostosomiasis

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To establish the scientific basis of the international control strategy of parasitic diseases, that has been advocated by Japanese Government, a collaborative study was carried out regarding soil-transmitted helminthiases and schistosomiasis as these two parasitic diseases had been effectively suppressed by school-health approach in Japan. These studies led us to obtain following results ; (1)When the prevalence of soil-transmitted helminth infection is low, e.g. less than 50%, mass examination and selected chemotherapy against only positive cases can be recommended ; however, if the prevalence is over 50% and the rate of enrollment in primary school is low like in Sub Saharan Africa, blanket treatment with albendazole seems more reasonable as judged from cost effectiveness etc. (2)A field study in Kenya demonstrated the safety of long period of administration of praziquantel ; however, the necessity to monitor the appearance of the drug resistant schistosomes should be stressed. (3)As … More one of the morbidities by schistosomiasis haematobia, irritating dysuria could be recognized among school children in the endemic area. (4)In regard to N. braziliensis infection as a model of hookworm diseases, an excretory-secretory substance was found to selectively inhibit γ-interferon production from T cells. Moreover, on the top portion of villi of intestine of the experimentally infected model, the activity of caspase3 was elevated, suggesting the dropping of epithelial cells is promoted by apotosis. In addition, a cell strain, IEC-6, was found toe be increasingly detached in the in vitro culture system by a substance from this parasite, and apotosis of this cell line was also promoted by the same substance. (5)Studies on development of effective vaccine against schistosomiasis was carried out, and suggested that calpain could be a candidate. Moreover, in the study of S. venezuelensis infection especially on the mechanism of its invasion into intestinal mucosa, an important role of sulfated carbohydrate localized in the mucosal tissue was demonstrated. (6)Studies on evaluation and development of rapid diagnostic test for soil-transmitted helminthiases indicated that Kato-Katz technique, which has been widely employed in the field surveillance, is not necessarily applicable to estimation of the prevalence, and sometimes reduces the reliability and effectiveness of such a field surveillance. (7)The current status of parasite control by school health approach was evaluated in Kenya and the surrounding countries, which demonstrated that the rate of infection with Schistosona haematobium reached 10-40% among school children in Kenya and Zanzibar. Accordingly school health approach could be regarded appropriate to solve these problems ; however, deworming in primary schools was attempted only at 22% and 65% in Kenya and Zanzibar, which should be improved. (8)Mapping of soil-transmitted helminth infections was carried out in Southeast Asia, which enabled us to utilize GIS for further analysis. The effectiveness of RS was also confirmed in Kenya, and if GIS is introduced based on epidemiological data of soil-transmitted helminthiases and schistosomiasis, detailed surveillance on these parasitic diseases seemed feasible. Less