# Antiviral Activity of Eugenol Against Chinese Rice-Field Eel Rhabdovirus in Monopterus albus

## TL;DR

Eugenol, a compound from clove plants, shows strong antiviral effects against a deadly virus in Chinese rice-field eels, improving survival and reducing viral load.

## Contribution

Eugenol is shown to inhibit CrERV replication both in vitro and in vivo, with a novel mechanism involving mitochondrial protection and gene regulation.

## Key findings

- Eugenol achieved a 96.6% inhibition rate in eel kidney cells at 40 mg/L.
- Eugenol improved survival rates by 56% in prevention and 48% in treatment experiments.
- Eugenol reduced viral load and upregulated antiviral and antioxidant genes.

## Abstract

Chinese rice-field eel rhabdovirus (CrERV) is a serious epidemic pathogen of Chinese rice-field eel and causes severe economic losses to aquaculture. Therefore, it is important to find an effective antiviral strategy to combat highly lethal CrERV outbreaks. Herbal plants have been widely used and play a vital role in disease treatment. This study aimed to evaluate the effect of the antiviral activity of eugenol against CrERV infection. The results demonstrated that eugenol can effectively inhibit CrERV replication both in vitro and in vivo. Furthermore, eugenol maintained cell morphology, attenuated CrERV-induced nuclear damage, and inhibited apoptosis by protecting mitochondrial membrane potential. It also improved the survival of Chinese rice-field eel, reduced viral load, and influenced CrERV infection by promoting the expression of antiviral-related genes. All the above results show that eugenol is a promising agent against CrERV in the fish industry.

Chinese rice-field eel rhabdovirus (CrERV) is a serious epidemic pathogen of Chinese rice-field eel and causes severe economic losses to aquaculture. However, there are no commercial drugs presently available to control CrERV infection. Eugenol is a bioactive compound extracted from clove plants and exhibits potential antiviral activity. In the study, the antiviral activity of eugenol against CrERV was investigated in Chinese rice-field eel (Monopterus albus). Eugenol reached the highest inhibition rate of 96.6% at 40 mg/L in Chinese rice-field eel kidney cells (CrEK). Notably, eugenol exhibits antiviral activity by directly targeting CrERV and additionally confers prophylactic effects against infection via its action on CrEK cells. The results of exploring the viral invasion cycle demonstrated that eugenol primarily exerted its antiviral effect during the middle stage and late stage (12 h and 24 h) of viral infection. In addition, eugenol inhibited CrERV-induced apoptosis of CrEK cells, maintained mitochondrial membrane potential levels, maintained physiological cellular morphology and structure, and protected cells from loss of cellular morphology, formation of apoptotic vesicles, and cell fragmentation. For the in vivo study, eugenol increased the survival rate of CrERV-infected rice-field eel by 56% and 48%, in prevention experiments and treatment experiments, respectively. Concurrently, eugenol significantly reduced viral loads and induced the upregulation of anti-inflammatory and antioxidant genes, indicating its potential for immunoregulation. In summary, eugenol holds potential for both preventing and treating CrERV infections in the aquaculture context.