Autogenous bacterins cross-protection as a trial for Streptococcosis control in Oreochromis niloticus

The present work investigated experimentally a rapid, effective and inexpensive control to streptococcosis, and the role of Streptococcus iniae as a major cause for mass mortalities of cultured Oreochromis niloticus in Kafrelsheikh, Egypt, in the summer of 2017; mass mortality was associated with poor water quality, and cultured naturally infected O. niloticus showed corneal opacity, congestion, and deep haemorrhagic ulceration in the dorsal region. S. iniae was identified as a causative agent by traditional and PCR techniques. The highest incidence of S. iniae was in the liver. Choosing vaccination as a control was experimentally investigated; the superiority of Streptococcus agalactiae FKC bacterin was related to the antibody titre, which was higher than S. iniae bacterin. The relative level of protection values were 79% and 23% in fish challenged with S. agalactiae and vaccinated with FKC of either S. agalactiae or S. iniae, respectively. These values were 56% and 74% in fish challenged with S. iniae and vaccinated with FKC of either S. agalactiae or S.i niae, respectively. In conclusions, autogenous bacterins of S. agalactiae or S.iniae induced cross-protection against S. agalactiae and S. iniae, in O. niloticus. The protection was superior to a S. agalactiae FKC vaccine, which could be a useful means for the prevention and control of streptococcosis.