Luteolin in Lonicera japonica inhibits the proliferation of white spot syndrome virus in the crayfish Procambarus clarkii

White spot disease caused by the white spot syndrome virus (WSSV) is a highly lethal infectious disease of crustacean aquaculture, with no effective means of control. Active compounds from herbal medicines are promising candidates for the development of antiviral agents for WSSV. We evaluated the efficacy of 12 herbal medicines in inhibiting WSSV proliferation in a WSSV infection model (Procambarus clarkii), Lonicera japonica extract had the strongest inhibitory effect on WSSV replication. Luteolin (LUT), the major bioactive compound of L. japonica extract, was further investigated and revealed to have a strong inhibitory effect on WSSV (96.04%, 50 mg/kg). LUT treatment decreased the WSSV load and the expression of important viral genes (immediate-early gene ie1, DNA polymerase DNApol and envelope protein Vp28) in a dose-dependent manner and increased the survival of WSSV-infected crayfish by 60.00% (50 mg/kg). Co-incubation and time-of-addition assays revealed that LUT did not affect the infectivity of viral particles or viral absorption and entry. Expression of immunerelated genes such as barrier-to-autointegration (BAF), heat shock protein 70 (Hsp70) and signal transducer and activator of transcription (STAT), which may be beneficial for viral replication, were significantly decreased (P < 0.01) in LUT-treated crayfish. LUT also modified the expression of antioxidants (SOD, CAT and GST), proinflammatory factor (COX-1 and COX-2), and apoptosis-related (BAX and BI-1) genes (P < 0.01) to enhance antioxidant defenses, mitigate inflammation and induce apoptosis, respectively. Overall, LUT could be used as a prophylactic or therapeutic agent against WSSV infection in crustacean aquaculture.