Increased protection of shrimp against white spot syndrome virus by oral administration of a major envelope protein: is vaccination reality?

Since the 1990s shrimp culture has been hampered by mass mortalities in ponds throughout the world. Penaeid shrimp are affected by many infectious agents, mainly of bacterial and viral origin, and especially by white spot syndrome virus (WSSV). The lattar has had a major impact on shrimp culture since its discovery in 1992 and it is still a major problem. The only measures presently used to control WSSV are rigorous sanitation and adequate health management practices. Alternative intervention strategies such as vaccination should be and are currently being explored. Recent experiments in the shrimp Penaeus monodon revealed that oral administration of the major envelope protein VP28 overexpressed in bacteria results in high protection levels compared to control groups (Fig. 1). Though these results are promising for the further development of a practical disease prevention strategy, the mechanism of the protection is unclear and it is important to understand it from a biological viewpoint. Shrimp and crustaceans in general are thought to lack a speciimmune system and thus to be unable to recognize, let alone respond specito, foreign proteins. Nevertheless, increased protection against disease has been observed by oral administration and intramuscular injection of WSSV structural proteins and this has been called a quasi-immune response. As long as the nature of these observed responses is unknown, we can only speculate on the processes involved. Is it a speciimmune response or is it the result of something different like competition for receptors? Another question is whether the protection is durable. Experiments designed to tackle these questions and answers to them will be discussed.