Schistosomiasis in the Republic of Sao Tome and Principe: Characterization of Schistosoma intercalatum

This paper reports the morphological and biochemical characterization of the species of Schistosoma infecting humans in the Republic of São Tomé and Principe. The eggs are typical in shape and size of S. intercalatum , measuring on average between 174·5 μm and 189·1 μm. The eggs are voided in the faeces and not the urine of infected people. The parasite experimentally develops in several different species of Bulinus belonging to the B. forskalii group, including B. forskalii , with a minimum prepatent period of 25 d, and also in snails of the B. reticulatus group ( B. wrighti ); it is incompatible with snails of the B. africanus and B. truncatus/B. tropicus complex. A survey of 5 different habitats at intervals of 2 weeks over a period of one year showed that populations of B. forskalii increased during the dry period of June, July and August in 1988, and in 3 of the habitats snails were present throughout the year. Hence transmission may take place in these habitats throughout the year. Preliminary evidence suggests that water velocity is a limiting factor confining Bulinus to the north-east of the island where the terrain is less mountainous. Development of schistosomes from São Tomé was followed in experimentally infected hamsters. The cross-over point (the point at which the paired male and female worms are of the same average length) occurred at about 49 d after infection: eggs were first seen in the uteri of the female worms 48 d after infection. The parasite from São Tomé developed in sheep and produced viable eggs. Analysis of restriction fragments of the rRNA gene clearly differentiated the São Tomé parasite from S. haematobium . Comparative scanning electron microscopy studies of the surface of the male worms of isolates from São Tomé revealed tubercles with spines, but with some variation in the degree of spination. A study of 9 different enzymes using isoelectric focusing indicated that hexokinase, acid phosphatase, and glucose-6-phosphate dehydrogenase were monomorphic in the São Tomé schistosome. ...