High susceptibility of Neotricula aperta gamma-strain from Krakor and Sdau in Cambodia to Schistosoma mekongi from Khong Island in Laos

Neotricula aperta γ-strain snails collected from Krakor and Sdau in Cambodia were found to have the same or higher susceptibility to Schistosoma mekongi as N. aperta originally isolated from Khong in Laos. Infection rates of N. aperta γ-strain snails exposed to 3 miracidia at week 8 were: Khong γ-strain, 22.6%; Krakor γ-strain, 33.3%; and Sdau γ-strain, 67.4%. At week 10, the Sdau γ-strain showed the highest infection rate of 83.3%. We thus found significantly high susceptibility of the Sdau γ-strain to S. mekongi originally isolated from Khong. However, in another experiment, susceptibility of the Sdau γ-strain was rather comparable to that of Khong and Krakor γ-strain. We also found no significant differences in infection and survival rates between the Khong and Krakor γ-strain when the snails were exposed to 3 or 6 miracidia. This is the first report to confirm the high susceptibility in the laboratory of N. aperta γ-strain snails from endemic areas in Cambodia to S. mekongi originally isolated from Laos. The high susceptibility of N. aperta γ-strain snails to S. mekongi in distant areas may be an important factor in the endemic transmission of human schistosomiasis.