Vacinas Orais e Parenterais contra Flavobacterium columnare: avaliação da resposta imune humoral por ELISA e de sua eficiência na imunização de tilápia do Nilo

Abstract

Flavobacterium columnare is a major bacterial pathogen for almost all freshwater fish species. It is responsible for outbreaks in fish farms worldwide, causing high mortality rates. Fish vaccination is a potential alternative for prevention and control of disease. Because of its easy application, low cost and minimum stress to fish, oral vaccines are a reasonable alternative to fish immunization. Alginate microparticles have been widely used as controlled release system, including for fish vaccination. The objectives of this work were to evaluate the capacity of oral and parenteral vaccines against F. columnare to induce humoral response, in vivo efficiency and the relation between antibodies levels and protection to Nile tilapia fingerlings. The fingerlings were immunized with bacterin by i.p., i.m. oral and immersion routes as well as orally with alginate microparticles incorporating formalin-killed bacteria. A sandwich ELISA was developed to detect specific antibodies against F. columnare. The animals were challenged with pathogenic strain BZ-1 to determine the relative percentage of survival. Significant humoral response were induced by bacterin administered by i.p. and i.m. (P < 0.05). However, no vaccine preparations were effective to protect fish against F. columnare infection (P < 0.05). In spite of high antibody levels, there was no relation between immunoglobulin titers and resistance to columnaris for Nile tilapia fingerlings. This data suggest that the use of serological analysis as the unique method to determine vaccine efficiency against F. columnare infection in Nile tilapia can result in imprecise determination of the usefulness of these products in vivo.