Immunoregulation and parasitic infections.

Abstract

Schistosomiasis is still widely distributed in 74 countries and territories and affects some 200 million people according to an estimation by WHO [1], despite the fact that extensive efforts to control the disease have been made in many endemic areas. Three species of the genus Schistosoma are the major pathogens of human schistosomiasis: Schistosoma japonicum distributed in China, the Philippines, and Indonesia, S. mansoni in many countries in Africa and South America, and S. haematobium distributed in Africa and the Middle East. The former two species reside in the portal vein system and cause intestinal or hepatosplenic schistosomiasis, while S. haematobium resides in the vesical plexus, resulting in urinary schistosomiasis. The recent outbreak of schistosomiasis in Senegal is a typical indication that the disease is emerging or re-emerging. The Diama Dam was constructed at St. Louis as a gate structure on the Senegal River in August 1986 to block saltwater intrusion during the dry season and it was in January 1988 that the first case of S. mansoni infection was diagnosed in Richard Toll, a city 100 km upstream of the mouth of the river, where the parasite had been unknown. Thereafter, the prevalence was up to 76% in the last quarter of 1989 [2]. Another example is Lake Volta, the largest artificial impoundment, that was created by the construction of a dam across the Volta River in Ghana in 1964. At that time, urinary schistosomiasis was found with a low prevalence of 5–10% in the area that was later to be impounded. Five years after the completion of the dam, the prevalence of S. haematobium infection reached about 90% in lakeside communities [3]. In fact, through epidemiological studies carried out by the support of the Japan International Cooperation Agency (JICA) in cooperation with counterparts of the …