IN a recent paper Cridland1 has stated among his conclusions that there is no evidence for the occurrence of strains in human schistosomes and also that he had found that certain species of snail did not appear to act as carriers. For example, he states that Bulinus africanus ovoideus (Bgt.) will not act as a carrier of Schistosoma haematobium in Uganda, on the evidence that he had not been able to infect it in the laboratory. In the Kitui area of Kenya Bulinus (Physopsis) africanus ovoideus (Bgt.) and B. (P.) nasutus (von Marts.) both occur in ponds, dams and streams. The latter snail is common also in the coastal regions of north-east Tanganyika and is, in my opinion, quite different from the snail occurring in the Great Lakes which Mandahl–Barth2 recorded as nasutus. He agrees with me that different sub-species are involved.
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Cridland, C. C., J. Trop. Med. (Hyg.), 58, 1 (1955).
Mandahl-Barth, G., Ann. Mus. Roy. Congo Belge, Sc. Zool., 32, 115 (1954).
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VERDCOURT, B. Possible Occurrence of Strains in Species of Schistosomes. Nature 180, 865–866 (1957). https://doi.org/10.1038/180865a0
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