Researchers at the National University of Singapore (NUS) and the Temasek Life Sciences Laboratory have developed an oral vaccine for fish that protects against the nervous necrosis virus (NNV). By encapsulating virus-like particles within Lactococcus lactis bacteria, the vaccine can be mixed directly into fish feed, offering a practical, labour efficient and cost-effective alternative to traditional injection-based immunization methods, according to a report published in the journal Fish & Shellfish Immunology.
Why is traditional fish vaccination failing the aquaculture industry?
Traditional vaccination protocols rely on individual injections, a process that can cause fish to be stressed. It is also impractical to execute on a large scale, and unsuitable to be administered on fish larvae and fingerlings. According to Professor Yang Daiwen from the Department of Biological Sciences at the NUS Faculty of Science, this approach is unsuitable for large-scale operations. Because NNV can cause a near 100 per cent mortality rate in the larval stage and reduce growth in survivors, the lack of simple and effective treatments has long hindered the aquaculture sector’s economic stability.
The vaccine developed by the NUS team reduces brain viral load in fish by about 300 times after fish were exposed to NNV for seven days, significantly limiting the virus’s ability to replicate.
How does the oral vaccine trigger an immune response?
The vaccine utilizes a two-part biological delivery system to bypass the digestive tract’s harsh environment. First, scientists created “imposter” viruses known as Virus-Like Particles (VLPs) using the NNV outer shell, or capsid protein. These VLPs mimic the virus externally but lack genetic material, making them incapable of causing disease while still training the immune system to recognize the threat.
To ensure these particles reach the gut intact, researchers encapsulated them within Lactococcus lactis, a safe and well-understood bacterium that acts as a protective capsule. According to the research team, trials showed that inactivating the bacteria with sodium hypochlorite was essential to maintaining the VLP structure and solubility, allowing for effective delivery to the fish’s immune system.
What are the economic benefits of this delivery method?
The oral vaccine provides a more cost-effective solution compared to feeding fish purified VLPs directly. According to data from the NUS research team, the bacterial encapsulation method induced two-times the levels of antibodies and neutralising antibodies compared to direct VLP feeding. This efficiency is critical for the commercial viability of farming species such as grouper, European seabass, and Asian seabass.
Pro Tip: The role of neutralizing antibodies
Neutralizing antibodies are essential for fish health because they bind to pathogens and prevent them from entering host cells. This preemptive defense is the primary mechanism by which the new oral vaccine prevents the lethal effects of NNV.
What is the future of NNV management?
The research team has filed three patents regarding this novel vaccine technology. Plans for the next phase of development include collaborating with industrial partners to conduct field trials on grouper and other types of fish. This shift from laboratory validation to real-world application aims to provide the aquaculture industry with a practical, labor-efficient tool for long-term disease management.
Frequently Asked Questions
- Can this vaccine cause the virus in fish? No. The vaccine uses non-infectious virus-like particles (VLPs) that contain no genetic material, meaning they cannot cause the disease.
- Which fish species can be treated? The vaccine can be applied to economically important species, including grouper, European seabass, and Asian seabass.
- Why is Lactococcus lactis used? It is a safe, well-understood bacterium that serves as a protective capsule, shielding the vaccine particles from the fish’s digestive system until they reach the gut.
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