Effects of Physicochemical Factors on Loss of Infectivity of Opisthorchis viverrini Cercariae

This study aims to develop an alternative field-based approach to interrupt the life cycle of O. viverrini. The effects of temperature, salinity, acidity, ultraviolet A, B, C radiation, and combinations of these physicochemical factors on the loss of infectivity of Opisthorchis viverrini cercariae were analyzed to determine values required for 50 and 95 % lethal concentrations (LC50 and LC95) and period of loss infection success (LI50 and LI95). Newly shed cercariae of O. viverrini were used. LC50 and LC95 values for temperature, salinity, and acidity on cercariae were 33.19 and 37.70 ºC, 7.29 and 8.40 ppt, 4.62 and 4.80 M H2CO3, respectively. The values of LI50 and LI95 on cercariae by exposure to UVA, UVB, and UVC were 19.54 and 20.11 h, 5.03 and 5.12 h, 3.37 and 6.02 min, respectively. Combinations of these factors in the presence of UVC proved damaging to cercariae most rapidly. The shortest loss infection time of LI50 and LI95 were 1.09 and 2.83 min. Cercariae were deemed to have lost the ability to infect cyprinid fish when they had shed their tails, even though they were still capable of some movement. In nature, temperature, salinity, acidity, ultraviolet radiation, and combinations of these factors, affect the ability of O. viverrini cercariae to infect cyprinid fish.