Susceptibility of juvenile Macrobrachium rosenbergii to different doses of high and low virulence strains of white spot syndrome virus (WSSV)

As some literature on the susceptibility of different life stages of Macrobrachium rosenbergii to white spot syndrome virus (WSSV) is conflicting, the pathogenesis, infectivity and pathogenicity of 2 WSSV strains (Thai-1 and Viet) were investigated here in juveniles using conditions standardized for Penaeus vannamei. As with P. vannamei, juvenile M. rosenbergii (2 to 5 g) injected with a low dose of WSSV-Thai-1 or a high dose of WSSV-Viet developed comparable clinical pathology and numbers of infected cells within 1 to 2 d post-infection. In contrast, a low dose of WSSV-Viet capable of causing mortality in P. vannamei resulted in no detectable infection in M. rosenbergii. Mean prawn infectious dose 50% endpoints (PID50 ml(-1)) determined in M. rosenbergii were in the order of 100-fold higher for WSSV-Thai-1 (10(5.3 +/- 0.4) PID50 ml(-1)) than for WSSV-Viet (10(3.2 +/- 0.2) PID50 ml(-1)), with each of these being about 20-fold and 400-fold lower, respectively, than found previously in P. vannamei. The median lethal dose (LD50 ml(-1)) determined in M. rosenbergii was also far higher (similar to 1000-fold) for WSSV-Thai-1 (10(5.4 +/- 0.4) LD50 ml(-1)) than for WSSV-Viet (10(2.3 +/- 0.3) LD50 ml(-1)). Based on these data, it is clear that juvenile M. rosenbergii are susceptible to WSSV infection, disease and mortality. In comparison to P. vannamei, however, juvenile M. rosenbergii appear more capable of resisting infection and disease, particularly in the case of a WSSV strain with lower apparent virulence.