Development of a new vaccine delivery method for fish: percutaneous administration by immersion with application of a...

A new administration method was developed for vaccination of juvenile rainbow trout against beta-haemolytic Streptococcus. This simple and convenient method was equal in effectiveness to intra-peritoneal injection. Small skin lesions were produced using a multiple puncture instrument while fish were immersed in a vaccine suspension containing formalin-killed Streptococcus iniae. Upon challenge 2 weeks after vaccination, mortality of fish vaccinated by this method was 40%, equal to that by intra-peritoneal injection, while non-vaccinated control fish and fish vaccinated by immersion (without multiple puncture) each experienced 80% mortality. High efficacy was obtained with the multiple puncture/immersion method even when vaccine was diluted 10-fold. Quantitative analysis using fluorescent microspheres revealed that both antigen uptake by skin and delivery to the kidney and spleen were more effective with this method than with immersion alone. Microspheres were found in the skin within the pinpoint lesions and pressure mark caused by multiple puncture instrument. The greater protection gained by the present method can be attributed to higher numbers of particulate antigens taken up by fish and delivered to the lymphoid tissues.