Influence of temperature and exposure time on the infectivity of Bohle iridovirus, a ranavirus

Abstract

This study examined the functional temperature range of a ranavirus outside host cells over increasing temperatures and exposure times and subsequently tested infectivity in cell culture. Initially, cell susceptibility was determined by incubating Bohle iridovirus (BIV) at 30°C, 40°C, 50°C and 60°C for 5, 30 and 60min and subsequently titrating samples in one epithelioma papulosum cyprinid (EPC) and two Bluegill fry 2 (BF2) lineages at 28°C. Titres obtained in the three cell lines were similar and EPC cells were subsequently used to further investigate ranavirus infectivity with two degree increments in temperature between 40°C and 60°C for 5, 30 and 60min. The rate of inactivation was found to be dependent on temperature and time of exposure. Bohle iridovirus could replicate in EPC cells following exposure to most temperatures and prolonged time, but titers were reduced as temperature and time of exposure increased. Viral titres were greatest (108 TCID50/ml) after exposure to 30°C and declined with increasing time of exposure and increasing temperature. Declines in BIV infectivity were largely between 40°C (108 TCID50/ml) and 44°C (105 TCID50/ml at 5 and 30min and 103.5 TCID50/ml at 60min) and secondly at temperatures greater than 52°C (from 103.5 TCID50/ml and approaching zero with increasing temperature and time). Treatment at 58°C for 60min and 60°C for 30 and 60min resulted in complete loss of BIV infectivity. The results from this study show that ranavirus can withstand much higher temperatures than previously thought, which is fundamental for understanding ranavirus epidemiology, indirect transmission dynamics and for biosecurity purposes.