Vaccination against streptococcal infections in farmed fish

Abstract

Aquaculture produces more than 50% of fish for human consumption and, in spite of major improvements since the adoption of injectable vaccines in the 1990s, bacterial diseases still account for considerable losses, particularly in tropical and warm temperate species. Streptococcosis, caused predominantly by Streptococcus iniae and S. agalactiae, manifests as a generalised septicaemia and meningitis followed by rapid mortality. Vaccination against streptococcal infections is difficult as a result of multiple, poorly defined serotypes and consequent vaccine escape (reinfection of previously vaccinated animals). However, genomics applied to reverse vaccinology is providing novel insights into diversity among these aquatic pathogens and is identifying cross-serotype targets that may be exploited for new generation streptococcal vaccines for aquaculture.