Oral Vaccination of Baculovirus-Expressed VP28 Displays Enhanced Protection against White Spot Syndrome Virus in Penaeus monodon

Overview:

WSSV, of the genus Whispovirus, is one of the most threatening infectious pathogens to the shrimp culture industry, meaning that any means of treating of vaccinating against this virus would be incredibly well received. WSSV usually has a mortality rate of 100% over a period of 2 to 5 days. Currently, no effective vaccines or adequate treatments are available. It is known to be difficult to vaccinate invertebrates due to the lack of a true adaptive immune response. Inverts rely solely on an innate immune response. It has been proved that a quasi-immune response exists which survives after exposure to the WSSV virus, creating some hope in the field.VP28 is one of five major structural proteins found in WSSV and studies show this protein is associated with the virion envelope. It is thought to be responsible for the initial viral infection. The authors of this experiment (Musthaq and Kwang), by inserting VP28 into a baculovirus, managed to get a VP28 protein expressed on the surface and use this as a method of VP28-based recombinant vaccination. This recombinant vaccine was named Bac-VP28. A construct that did not have the VP28 gene was termed Bac-wt. The amount of VP28 present in Bac-VP28 was measured as 65.3micrograms per ml and considered as an abundant quantity.

Oral Vaccination Results:

Shrimp were orally administered Bac-VP28, Bac-wt and PBS respectively (groups 1-3). Bac-VP28 and Bac-wt coated feed was administered continuously for 7 days before the shrimp were subsequently challenged with the WSSV. Batch 1 and 2 were treated identically, except batch 1 received a WSSV dose of 3dpv and batch 2 received a dose of 15dpv.

In all cases, the positive control group (3) showed 100% mortality, as did group 2, treated with the Bac-wt. The group (1) treated with Bac-VP28 however showed only an 18.3% (batch1) and 23.3% (batch2) mortality rate, which is significantly reduced.

A negative control group (without the virus) showed no mortality.

Immersion Vaccination Results:

As with the oral vaccination, there were the 3 groups, Bac-VP28 (1), Bac-wt (2) and PBS (3). Instead of through feed, they were vaccinated through immersion in a solution. Again, all shrimps in batch 1 were challenged with WSSV at 3dpv and those in batch 2 challenge with WSSV at 15dpv.

All of group 2 (Bac-wt) and 3 (PBS) showed 100% mortality, yet those treated in group 1 (Bac-VP28) showed a mortality rate of only 25% (batch1) and 31.6% (batch2). This was a significant decrease in mortality rate.

Summary

The use of baculovirus as a vector for vaccination has been shown to be effective when present in oral and immersion vaccination, yet more so when administered orally. Further tests need to be carried out to ensure that this test creates an immune memory response, but the results have presented avenues down which further trials can be created.


Syed MS, Kwang J (2011) Oral vaccination of baculovirus-expressed VP28 displays enhanced protection against White Spot Syndrome Virus in Penaeus monodon. PLOS ONE 6: e26428.10.1371/journal.pone.0026428 PubMed: 22069450.