Electrophoretically-detected allozyme variation reveals only moderate differentiation between Chinese and Philippine Schistosoma japonicum

A number of discrete strains of Schistosoma japonicum have been described of which those from China and the Philippines are the most important in terms of public health significance. The strains have previously been shown to differ in a number of biological characteristics and isoenzyme analysis has established that Chinese and Philippine S. japonicum are, especially, quite distinct. As few direct genetic differences have been identified, with nuclear and mitochondrial genetic markers being shown earlier to be highly conserved between the two forms (Bowles et al., 1993), enzyme electrophoresis was performed to re-evaluate whether the two strains are as genetically diverse as field and laboratory maintained isolates previously examined using this approach. Some allelic differences were evident between Chinese and Philippine S. japonicum but the genetic distance (a measure of genetic relatedness), D = 0.272, between the two strains was, however, considerably smaller than the earlier obtained estimates of D > 0.4–0.575. In addition to the enzyme studies, restriction patterns, obtained using 4-base cutting restriction enzymes and hybridisation with DNA probes comprising the entire ribosomal DNA (rDNA) repeat unit of S. mansoni, were indistinguishable between the Chinese and Philippine forms of S. japonicum, thereby re-emphasising their remarkable similarity at the genetic level.