Efficacy of Ultraviolet Light Disinfection of the Waterborne Microsporidian Pathogen Ecytonucleospora hepatopenaei (EHP)

Abstract

The microsporidian Ecytonucleospora hepatopenaei (EHP) is an environmentally persistent, waterborne pathogen that threatens global shrimp aquaculture. This study evaluated the effectiveness of medium-pressure ultraviolet (MPUV) irradiation for disinfecting the unculturable EHP spores in water. Spore viability was assessed using a modified dual-fluorescence staining method. MPUV-induced DNA damage of spores was evaluated through both conventional PCR and quantitative PCR (qPCR) targeting the spore wall protein (SWP1) and small subunit ribosomal RNA (SSU) genes. Results showed that MPUV irradiation induced a significant, dose-dependent inactivation of EHP spores. A low dose of 27.6 mJ/cm² did not significantly increase mortality compared to the control, whereas doses of 55.2–273.0 mJ/cm² produced progressively higher mortality. At intermediate exposures, some spores initiated but failed to complete polar tube ejection, forming only small buds, indicating the loss of infectivity. High doses of 216.0 and 273.0 mJ/cm² yielded spore mortality rates of 95.67% and 97.14%, respectively, with no spore germination or budding observed. Molecular analyses confirmed that substantial DNA damage in EHP spores and suggested that the SWP1 gene is a more reliable indicator of this damage than the SSU gene. These findings establish MPUV as an effective, chemical-free disinfection strategy, providing practical dosing guidelines for preventing EHP transmission in water treatment and aquaculture biosecurity.