Withania somnifera attenuates Tilapia lake virus (TiLV)‐induced mortality by inhibiting stress and strengthening the innate antioxidant defence system

Abstract

Tilapia lake virus (TiLV) disease is an emerging disease threatening the aquafarming industry. It is spreading rapidly and has resulted in significant mortalities in tilapia, thus seriously affecting the economy of the farmers globally. Mortality due to TiLV infection is mostly stress-associated. Withania somnifera (WS) is a medicinal plant whose roots are well known to reduce stress and improve immunity. This study evaluated the role of oxidative stress induced by TiLV on tilapia and the stress-reducing effect of aqueous root extract of WS (WSE) on TiLV-infected tilapia. TiLV-induced continuous daily mortality with severe clinical signs in heavily infected (first step reverse transcriptase-polymerase chain reaction (RT-PCR) positive) tilapia, whereas the lightly infected (semi-nested RT-PCR positive) tilapia exhibited mild clinical signs and fewer mortalities. Altered haematological parameters (Haemoglobin, protein, albumin, glucose and triglycerides), deteriorated innate antioxidant defence (glutathione peroxidase, catalase and superoxide dismutase), increased free radical generation, lipid peroxidation and stress-related inflammatory markers (interleukin-1β, tumour necrosis factor-α and cortisol) were observed in TiLV-infected tilapia, which were significantly reverted by the WSE treatment in heavily infected tilapia. The WSE treatment exhibited significant amelioration in liver pathology and ceased mortality within two weeks. The result obtained under laboratory conditions was corroborated with field studies in various parts of Kerala, India, which confirmed zero mortality and complete recovery of clinical signs in 10 TiLV-infected farms after the application of WSE. Overall results demonstrate the treatment potential of WSE via its anti-stress and antioxidant properties in attenuating TiLV induced pathology and mortality in tilapia.