Streptococcosis a Re-Emerging Disease in Aquaculture: Significance and Phytotherapy
2022
Hien Van Doan | Mehdi Soltani | Alexandra Leitão | Shafigh Shafiei | Sepideh Asadi | Alan J. Lymbery | Einar Ringø
Streptococcosis, particularly that caused by <i>S. iniae</i> and <i>S. agalactiae</i>, is a major re-emerging bacterial disease seriously affecting the global sustainability of aquaculture development. Despite a wide spread of the disease in aquaculture, few studies have been directed at assessing the in vitro antagonistic activity and <i>in vivo</i> efficacy of medicinal herbs and other plants against streptococcal agents. Most <i>in vitro</i> studies of plant extractives against <i>S. iniae</i> and <i>S. agalactiae</i> have found antibacterial activity, but essential oils, especially those containing eugenol, carvacrol or thymol, are more effective. Although essential oils have shown better anti-streptococcal activity in <i>in vitro</i> assays, <i>in vivo</i> bioassays require more attention. The extracts examined under in vivo conditions show moderate efficacy, increasing the survival rate of infected fish, probably through the enhancement of immunity before challenge bioassays. The available data, however, lack dosage optimization, toxicity and bioavailability assays of a specific plant or its bioactive compound in fish organs; hence, it is difficult to judge the validation of clinical efficacy for the prevention or treatment of fish streptococcosis. Despite the known bioactive compounds of many tested plants, few data are available on their mode of action towards streptococcal agents. This review addresses the efficacy of medicinal plants to fish streptococcosis and discusses the current gaps.
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