a1 Department of Social and Environmental Medicine, Faculty of Tropical Medicine, Mahidol University, 420/6 Rajavithi Road, Bangkok 10400, Thailand
a2 Department of Zoology, The Natural History Museum, Cromwell Road, South Kensington, London, SW7 5BD, UK
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 Kratié District, eastern Cambodia. The infection rates were: 3.0%, α-strain; 6.0%, β-strain; and 20.5%, γ-strain. The greater infectivity to the γ-strain, over both the α- and β-strains, was statistically significant. Comparisons of infectivity patterns for the Kratié isolate, with those described in earlier studies using S. mekongi isolates from southern Laos, revealed differences among the strains. The γ-strain of N. aperta is responsible for endemic transmission of human schistosomiasis in southern Laos and at Kratié. 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.
(Accepted February 12 1997)