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 Sao Tome and Principe. The eggs are typical in shape and size of S. interc alatum, measuring on average between 174.5 mu m and 189.1 mu m. The eg gs are voided in the faeces and not the urine of infected people. The parasite experimentally develops in several different species of Bulin us belonging to the B. forskalii group, including B. forskalii, with a minimum prepatent period of 25 d, and also in snails of the B. reticu latus group (B. wrighti); it is incompatible with snails of the B. afr icanus and B. truncatus/B. tropicus complex. A survey of 5 different h abitats at intervals of 2 weeks over a period of one year showed that populations of B. forskalii increased during the dry period of June, J uly and August in 1988, and in 3 of the habitats snails were present t hroughout the year. Hence transmission may take place in these habitat s throughout the year. Preliminary evidence suggests that water veloci ty is a limiting factor confining Bulinus to the north-east of the isl and where the terrain is less mountainous. Development of schistosomes from Sao Tome was followed in experimentally infected hamsters. The c ross-over point (the point at which the paired male and female worms a re 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 infe ction. The parasite from Sao Tome developed in sheep and produced viab le eggs. Analysis of restriction fragments of the rRNA gene clearly di fferentiated the Sao Tome parasite from S. haematobium. Comparative sc anning electron microscopy studies of the surface of the male worms of isolates from Sao Tome revealed tubercles with spines, but with some variation in the degree of spination. A study of 9 different enzymes u sing isoelectric focusing indicated that hexokinase, acid phosphatase, and glucose-6-phosphate dehydrogenase were monomorphic in the Sao Tom e schistosome. Intra-specific variation was noted for phosphoglucomuta se, glucose phosphate isomerase, alpha-glycerophosphate dehydrogenase, adenylate kinase, lactate dehydrogenase, and malate dehydrogenase. Th ese observations confirm the identity of the human schistosome in Sao Tome as S. intercalatum.