Transmission of Opisthorchis viverrini, Schistosoma mekongi and soil-transmitted helminthes on the Mekong Islands, Southern Lao PDR oleh Youthanavanh Vonghachack, Peter Odermatt, Keoka Taisayyavong, Souphanh Phounsavath, Kongsap Akkhavong, Somphou Sayasone