However,it has been found that many virulence factors,such as flagellin,hemolysin,outer membrane proteins,lipopolysacchride may play important roles in the development of this disease.

• 其发生机制至今不明,但是已发现许多毒力因子如鞭毛蛋白、溶血素、外膜蛋白、脂多糖等在其致病过程中有重要作用。