Nervous necrosis virus can kill nearly all larval fish in an affected population and stunt the survivors, making it one of the costliest pathogens in marine aquaculture. Conventional vaccination requires injecting each animal individually, which is stressful, labour-intensive and simply impractical for very young or very numerous fish. Researchers from the NUS Department of Biological Sciences, working with Temasek Life Sciences Laboratory, have developed an oral alternative that mixes into feed.
The formulation pairs two components. Virus-like particles are assembled from the pathogen's outer shell protein, so they present the viral surface to the immune system while being incapable of causing infection. These are then combined with Lactococcus lactis, a safe bacterium that carries the particles intact through the digestive tract to the gut, where the immune response can be mounted. Delivery, not antigen design, was the limiting problem.
The paired approach substantially outperformed feeding purified particles alone. Antibody levels were roughly double, including neutralising antibodies, and after exposure to the virus brain viral load fell by about 300 times. Findings were published in Fish and Shellfish Immunology. Three patents have been filed, and field trials with industry partners are planned on grouper and on both European and Asian seabass.
For aquaculture research the result is interesting as a template. Oral vaccination has been pursued for decades and has repeatedly failed on gut survival rather than immunogenicity. Using a food-grade bacterium as a protective carrier addresses that specific bottleneck, and if it generalises to other fish pathogens it would change the economics of disease control in hatcheries across tropical Asia.