NUS scientists have developed an oral vaccine to protect fish from the deadly nervous necrosis virus (NNV), a significant threat to the aquaculture industry. This breakthrough could revolutionize disease management in aquaculture, a vital sector that provides a substantial food source. The vaccine's unique approach involves using virus-like particles (VLPs) and a safe bacterium, Lactococcus lactis, to deliver the vaccine orally, offering a practical and efficient solution for immunizing large fish populations.
The vaccine's development addresses a critical challenge in aquaculture. Traditional vaccination methods, involving individual injections, are stressful for fish and impractical for large-scale application. Oral vaccinations, mixed into fish feed, offer a more labor-efficient and cost-effective alternative. The vaccine is particularly crucial for fish larvae and juveniles, which are highly vulnerable to NNV with a near 100% mortality rate during the larval stage and reduced growth even if some survive.
The vaccine's core components are innovative. Firstly, the researchers created VLPs using the NNV outer shell, known as the capsid protein. These VLPs are hollow, non-infectious replicas of the virus, triggering an immune response without causing disease. Secondly, Lactococcus lactis, a safe bacterium, acts as a delivery vehicle, encapsulating the VLPs and ensuring they reach the fish's gut, where an immune response is triggered.
A significant challenge was finding the optimal formula for the bacterium-encased VLPs. Trials with live and heat-treated Lactococcus lactis revealed that inactivating the bacteria with sodium hypochlorite protected the VLP's structure and solubility, ensuring effective delivery to the immune system. This innovation resulted in outstanding vaccine performance, inducing two-times the levels of antibodies and neutralizing antibodies compared to feeding purified VLPs directly.
The vaccine's effectiveness was further demonstrated by its ability to reduce brain viral load by about 300 times after fish exposure to NNV for seven days. This dramatic reduction in viral replication effectively protected fish from the lethal effects of the disease. The vaccine's success opens up possibilities for its application to economically important fish species such as grouper and European and Asian seabass.
The research team has filed three patents for this novel vaccine and aims to collaborate with industrial partners for field trials. This development is a significant step forward in aquaculture, offering a promising solution to a deadly virus that has caused substantial economic losses in the industry. The oral vaccine's practical and efficient nature could potentially transform disease management in aquaculture, ensuring the health and productivity of fish populations.
