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White spot syndrome virus (WSSV) is a major pathogen in shrimp culture because of its high infectivity, fast transmission speed, and high fatality rate. White spot disease (WSD), caused by WSSV poses a substantial threat to shrimp production. Therefore, it is crucial to identify effective antiviral agents to mitigate the economic loss caused by WSD. In this study, we prepared 20 ethanol extracts of Chinese herbal medicines (CHMs) and evaluated their anti-WSSV effectiveness using Litopenaeus vannamei larvae as a model. Among the tested extracts, Punica granatum L. exhibited the highest inhibition of WSSV infection at 85%, followed by Gentiana macrophylla at 79% and Isatis tinctoria L. at 63%. Quercetin, an active ingredient found in P. granatum at a concentration of 6.3 μM, increased the survival rate of WSSV-infected larvae by 30% after 72 hpi, and significantly inhibited WSSV infection. Further data from pre-incubation assays indicated that quercetin exhibited a potentially destructive effect on WSSV virions, thereby reducing the virulence and blocking viral horizontal transmission. Moreover, the high stability of the aquacultural water facilitated the continuous exchange of quercetin treatment, which further prolonged the survival time of WSSV-infected shrimp such that the survival rate was still at 13% after 5 days. These results highlight the potential application of quercetin in eliminating WSSV during shrimp larval production. • Pomegranate and quercetin showed anti-WSSV activity in water. • Quercetin blocked horizontal transmission of WSSV virions by reducing its infectivity. • Quercetin was stable in water and had therapeutic effect on WSSV-infected shrimp. [ABSTRACT FROM AUTHOR]

White spot syndrome virus (WSSV) is a pathogen that can infect many crustaceans, and that has caused huge economic losses in the shrimp industry. No effective prevention and control measures are currently available. In the present study, the ethanolic extract of Scutellaria baicalensis (SBEE) at 200 mg/L provided >50% protection for WSSV-infected shrimp larvae, and baicalein at 100 μM, one of the main anti-WSSV active substances in S. baicalensis , was 66.7% effective. When shrimp larvae were infected with WSSV after 8 h of SBEE and baicalein preincubation, the respective copy numbers of the viral genome were decreased by 31% and 46% versus the control group. Similarly, WSSV genome copy number reductions of 49% and 55% were observed in WSSV-infected shrimp larvae after 72 h of SBEE and baicalein immersion, respectively. In addition, SBEE or baicalein continuous treatment significantly reduced the viral loads in vivo , effectively blocking the horizontal transmission of WSSV between hosts. SBEE or baicalein also enhanced the expression of Toll4, Dorsal and antimicrobial peptides (AMPs) to restrict WSSV infection. In conclusion, S. baicalensis and baicalein are promising feed additives and immune enhancers for the control of WSSV infection. • Baicalein from Scutellaria baicalensis exhibits an anti-WSSV activity. • Baicalein blocks WSSV transmission in shrimp. • Baicalein enhances the immune resistance of shrimp to WSSV. [ABSTRACT FROM AUTHOR]