Evaluation of a range of doses of ultraviolet irradiation to inactivate waterborne actinospore stages of Myxobolus cerebralis

The ability of a range of doses of ultraviolet irradiation (UV) to inactivate the waterborne actinospore or triactinomyxon stages (TAMs) of Myxobolus cerebralis was evaluated by infectivity for juvenile rainbow trout Oncorhynchus mykiss. TAMs were UV-irradiated using a low pressure mercury vapour lamp collimated beam apparatus. All doses 40, 80, 120 and 160 mJ cm(-2) were found to completely inactivate the TAMs as demonstrated by the absence of microscopic lesions, myxospores and parasite DNA detected by quantitative PCR (qPCR) among rainbow trout 5 mo post-exposure. In contrast, rainbow trout receiving the same concentrations of untreated TAMs (1000 fish(-1)) developed clinical signs of whirling disease at 2 mo post-exposure and had severe microscopic lesions, high myxospore counts and high qPCR values when examined at 5 mo following exposure to the parasite.