Effects of dietary supplementation of Anabaena sp. PCC7120 expressing VP28 protein on survival and histopathology after WSSV infection in Macrobrachium nipponense.

Shrimp are especially susceptible to the White Spot Syndrome Virus (WSSV). Oral administration of the WSSV envelop protein VP28 is a promising approach to protect shrimp against WSSV. In this study, Macrobrachium nipponense (M. nipponense) were fed for 7 days with food supplemented with Anabaena sp. PCC 7120 (Ana7120) expressing VP28 and then challenged with WSSV. The survival rates of M. nipponense in three groups, including control, WSSV-challenged, and VP28-vaccinated, were subsequently determined. We also determined the WSSV content of different tissues and the tissue morphology in the absence of and after viral challenge. The survival rate of the positive control group (no vaccination and challenge, 10%) and empty vector group (fed with Ana7120 pRL-489 algae and challenged, 13.3%) was much lower than the survival rate of M. nipponense in wild type group (fed with Ana7120 and challenged, 18.9%), immunity group 1 (fed with 3.33% Ana7120 pRL-489-vp28 and challenged, 45.6%) or immunity group 2 (fed with 6.66% Ana7120 pRL-489-vp28 and challenged, 62.2%). RT-qPCR showed that WSSV content of the gill, hepatopancreas and muscle of immunity groups 1 and 2 were substantially lower than the positive control. Microscopic examination revealed that WSSV-challenged positive control exhibited large number of cell rupture, necrosis, nuclear exfoliation in gills and hepatopancreatic tissues. The gill and hepatopancreas of immunity group 1 showed partial symptoms of infection, yet the tissue was visibly healthier than that of the positive control group. No symptoms were visible in the gills and hepatopancreatic tissue of immunity group 2. The results demonstrate that the probability of M. nipponense infected by WSSV can be diminished by oral administration of cyanobacteria-expressed VP28. Such an approach could improve the disease resistance and delay the death of M. nipponense in the commercial production of this shrimp.