The sporicidal activity of chlorine dioxide gas on <i>Paenibacillus larvae</i> spores

American foulbrood disease (AFB) is an economically important, reportable bacterial infection of honey bees (Apis mellifera) caused by the spore-forming pathogen Paenibacillus larvae. Currently, there are no viable measures for treating P. larvae infected hives other than incineration. The objective of this study was to determine the activity of chlorine dioxide (ClO2) gas against P. larvae spores. Sporicidal efficacy was dependent on treatment time and gas concentration with effective ClO2 concentrations of 645 ng/ml for 30 min, 195 ng/ml for 1 h, 21 ng/ml for 2 h, or 16 ng/ml for 4 h. Treatment of surfaces with 230 ng/ml ClO2 for one h or 195 ng/ml ClO2 for 2 h completely inactivated P. larvae spores.