An Oral Vaccination Method with the Aid of Capsaicin against Viral Nervous Necrosis (VNN)

To develop an oral vaccination method for viral nervous necrosis (VNN) caused by piscine nodavirus (betanodavirus), sevenband grouper Epinephelus septemfasciatus was immunized with inactivated redspotted grouper nervous necrosis virus (RGNNV) vaccine. Seven-day consecutive oral administration of the RGNNV vaccine via feed failed to induce protection in fish against the virus challenge at 21 days post-immunization. However, anal intubation of the vaccine conferred protective immunity on fish, although virus neutralizing antibodies could not be detected. Similar protective immunity was also confirmed by oral administration of vaccine via feed supplemented with capsaicin, suggesting that capsaicin modulated the intestinal mucosal barrier to induce immune response.