The efficacy of Streptococcus agalactiae vaccine preparations, administered to tilapia broodstock, in preventing streptococcosis in their offspring, via transfer of maternal immunity

Abstract

This study aims to evaluate the efficacy of Streptococcus agalactiae vaccine preparations, administered to tilapia broodstock, in preventing streptococcosis, through specific and non-specific immunity being transferred to the offspring. The study was conducted in two phases. The first was the vaccination of the broodstock using a whole-cell vaccine, an extracellular product (ECP) vaccine, and a combination of the two with a ratio of 1:1. The vaccines were administered to the broodstock 2 and 3 weeks before spawning. The second phase was the challenge test for larvae produced by vaccinated broodstock, and larvae from the unvaccinated control broodstock, through immersion in a suspension of 107 cfu mL−1 pathogenic S. agalactiae for 30 min, at ages 7, 14, 21, and 28 days post-hatching. The parameters evaluated were the broodstock’s blood profile, antibody-lysozyme (in broodstock, eggs, and larvae), and the larvae’s relative percent survival. Treatment with the combined vaccine administered 3 weeks before spawning resulted in the broodstock having significantly better antibody levels, lysozyme activity, and hematology profiles, compared to the other treatments (p < 0.05). In addition, the larvae produced by broodstock subjected to this treatment, when challenged with the pathogenic S. agalactiae at ages 7, 14, 21, and 28 days, had RPS values of 95.24, 83.33, 72.22, and 56.02%, respectively. It was concluded that the administration of the “whole-cell/ECP” combination vaccine preparation to tilapia broodstock in the 3 weeks before spawning can increase specific and non-specific immunity in the broodstock and protect the larvae from S. agalactiae infection.