In order to understand the pathogen and pathogenesy of the disease, the aetiology, pathology and virulence factors were studied.

• 本试验对其病原学、病理学及致病因子的致病作用等进行了研究，其目的在于搞清该病的病原与致病机理，为养殖生产中有效地诊断和防治该病提供科学依据。