The changes in mortalities ofPenaeus monodon(with 1×10⁵ copies/g WSSV),WSSV loads in muscle,THC and the percentage of different types of haemocyte were studied by injection with WSSV solution containing 3×10³,6×10²,2×10²copies/mL virus and PBS.Real-time PCR,and microscopical examination were used in this experiment.The results showed that the cumulative mortalities were 93.33%±2.89%,56.67%±5.77%,45.00%±5.00% respectively,when the concentration of WSSV solution were 3×10³,6×10²,2×10² copies/mL.No death was observed in the PBS group.When the concentration of WSSV solution was 3×10³copies/mL,the virus load in the muscle reduced to minimum(3.54×10⁴copies/g)at 30 min postinjection,and reached its maximum(3.12×10⁸copies/g)at 48 h postinjection,then decreased again.For the other two experiment groups,the minimal virus load(1.11×10⁵,9.54×10⁴copies/g)in the muscle was observed at 1 h post-injection and the highest virus load(1.48×10⁷,5.46×10⁶copies/g)occurred at 48 h post-injection,but a second highest virus load(1.58×10⁵,1.11×10⁵copies/g)appeared at 6 h post-injection.No significant changes were found in the WSSV load of the control group throughout the experiment.The fluctuation range and the peak time of total haemocyte count(THC)were different between different dosage of WSSV solution.Especially THC reduced to minimum(3.48×10⁶,4.05×10⁶/mL)at 12 h and 48 h post-injection with 3×10³ copies/mL solution.The variation of THC and WSSV load were negatively correlated except individual time points.Under all groups,the percentage of semi-granular cells showed upward trend obviously early post infection,but later remained at a high level although fluctuated; the percentage of granular and hyalinocyte cells showed downward trend early postinjection significantly,while increased slightly in the middle period,but the percentage of granular cells at the later stage of post-infection was significantly lower than that of early period,while the levels of hyaline cells between later and early stages of post-injection have no significant difference.