Between the collection period, the variation is not remarkable either in the prevalence of shrimp that had WSSV, YHV and TSV or in infecting intensity of these three viruses except MBV.

• 结果显示，草虾的MBV带原率除自1994、1995年的86%25显著降2004、2005年的42%25，草虾感染MBV的严重性亦显著下降。