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

White spot syndrome virus infection in P. vannamei and M. rosenbergii: experimental studies on susceptibility to infection and disease

Since its appearance in the early 90’s, White Spot Syndrome Virus (WSSV) has continuously caused devastating outbreaks of penaeid shrimp mortality, from the shores of South-East Asia, all over Latin-America and more recently in all middleeastern countries were shrimp culture had only started to expand. In all that time, only limited progress has been made in reducing the impact of the virus on shrimp production. Unlike with many of the other shrimp viruses circulating in the culture ponds, no signs of resistance against WSSV infection and disease in penaeid shrimp have been documented

Rahman M.M., Escobedo-Bonilla C.M., Corteel M., Wille M., Alday-Sanz V., Pensaert M.B., Sorgeloos P. and Nauwynck H.J. Evaluation of virulence of three white spot shrimp Litopenaeus vannamei. Aqua 2006, Joint International Conference & Exhibition of European Aquaculture Society & World Aquaculture Society. Florence, Italy

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Purification of white spot syndrome virus by iodixanol density gradient centrifugation

Up to now, only a few brief procedures for purifying white spot syndrome virus (WSSV) have been described. They were mainly based on sucrose, NaBr and CsCl density gradient centrifugation. This work describes for the first time the purification of WSSV through iodixanol density gradients, using virus isolated from infected tissues and haemolymph of Penaeus vannamei (Boone). The purification from tissues included a concentration step by centrifugation (2.5 h at 60 000 g) onto a 50% iodixanol cushion and a purification step by centrifugation (3 h at 80 000 g) through a discontinuous iodixanol gradient (phosphate-buffered saline, 5%, 10%, 15% and 20%). The purification from infected haemolymph enclosed a dialysis step with a membrane of 1 000 kDa (18 h) and a purification step through the earlier iodixanol gradient. The gradients were collected in fractions and analysed. The number of particles, infectivity titre (in vivo), total protein and viral protein content were evaluated. The purification from infected tissues gave WSSV suspensions with a very high infectivity and an acceptable purity, while virus purified from haemolymph had a high infectivity and a very high purity. Additionally, it was observed that WSSV has an unusually low buoyant density and that it is very sensitive to high external pressures