Infectivity of a Cambodian isolate of Schistosoma mekongi to Neotricula aperta from northeast Thailand

All three strains of Neotricula aperta (Gastropoda: Pomatiopsidae) sampled from populations in northeast Thailand were found to be compatible with a Schistosoma mekongi isolate from Kratie District, eastern Cambodia. The infection rates were: 3.0%, alpha-strain; 6.0%, beta-strain; and 20.5%, gamma-strain. The greater infectivity to the gamma-strain, over both the alpha- and beta-strains, was statistically significant. Comparisons of infectivity patterns for the Kratie isolate, with those described in earlier studies using S. mekongi isolates from southern Laos, revealed differences among the strains. The gamma-strain of N. aperta is responsible for endemic transmission of human schistosomiasis in southern Laos and at Kratie. Consequently, the findings of this study are of use in the prediction of changes in the distribution of Mekong schistosomiasis, particularly its introduction to northeast Thailand from the neighbouring countries, Cambodia and Laos.