Abstract:Given its rich nutritional and medicinal values, the Chinese soft-shelled turtle (Trionyx sinensis) is considered a particularly important aquacultural species. However, intensive farming has led to frequent outbreaks of bacterial and viral diseases, causing substantial economic losses to the turtle farming industry. In recent years, viral mumps, caused by the pathogen T. sinensis hemorrhagic syndrome virus (TSHSV), has emerged as among the more harmful viral diseases affecting T. sinensis. TSHSV is an enveloped single-stranded RNA virus with a diameter of 60–80 nm that was the first discovered arteritis virus infecting amphibians and reptiles. The main clinical symptoms of TSHSV infection include multi-organ hemorrhage, which is associated with a high rate of mortality. However, there are currently no effective treatments for TSHSV. Although numerous studies have demonstrated that vaccines can be highly effective in preventing viral diseases in aquatic animals, TSHSV is characterized by antibody-dependent enhancement, in which stimulation by polyclonal antibodies promotes a significant upregulation of the antiviral genes rsad2 and mx2, as well as increases in viral copy number. Consequently, there is an urgent need to identify alternative effective technical approaches for the prevention of TSHSV. Given their safety, efficacy, minimal toxic side effects, low risk of resistance development, and reduced drug residues, Chinese herbal medicines meet the requirements of environmentally friendly aquaculture. Additionally, they are beneficial with respect to consumer health, and have accordingly gained widespread application in the prevention and treatment of diseases in aquatic animals. In this regard, Jiao et al. found that curcumin could enhance the survival of T. sinensis infected with TSHSV and inhibit viral proliferation in vivo. However, apart from this finding, to date, no other preventive measures against TSHSV have been discovered. The purple coneflower (Echinacea purpurea) is among the widely used herbs available on the international herbal market and is known for its antibacterial, antiviral, anti-inflammatory, and immunomodulatory effects. Among its active constituents, polysaccharides are considered among the main compounds contributing to the medicinal properties of E. purpurea. Luettig et al. discovered that different concentrations of E. purpurea polysaccharide (EPP) can stimulate macrophages to release tumor necrosis factor α (tnf-α) and interferon β (ifn-β), thereby enhancing immune activity. Furthermore, it is noteworthy that studies conducted to date have also found that EPP can alleviate viral infections both in vitro and in vivo. For example, in vivo experiments have revealed that EPP can significantly inhibit lesions caused by influenza A virus infection in mice, whereas, in vitro, it has been demonstrated that L926 cells treated with EPP are characterized by resistance to herpes simplex virus (HSV-I) infection. In addition, the E. purpurea preparation echinacein has been shown to inhibit the replication of EMC-virus and vesicular stomatitis virus (VSV), have certain inhibitory effects on SARS-CoV-2 and HIV, and can confer protective effects in pigs infected with porcine reproductive and respiratory syndrome virus (PRRSV). However, to date, there have been no reports regarding the protective effects of EPP against viruses infecting aquatic animals. Early studies in this field have revealed that TSHSV and PRRSV are both arteriviruses, and it is accordingly reasoned that EPP may also have protective effects in soft-shelled turtles infected with TSHSV. Consequently, in order to assess the therapeutic effects of EPP on T. sinensis mumps, in this study, we sought to determine the antiviral and immunomodulatory effects of EPP on TSHSV infection in T. sinensis based on hematoxylin and eosin (HE) staining, qRT-PCR, and tissue immunofluorescence analyses. The results revealed that at a concentration of 500 mg/kg, EPP can contribute to enhancing the survival of soft-shelled turtles infected with TSHSV, significantly reduce viral loads in the spleen and lungs, and alleviate damage caused to tissues and organs, such as the spleen, liver, kidneys, and lungs. In addition, mRNA expression levels of the antiviral-related genes rsad2 and usp18 were found to be lower in the EPP-treated individuals. In summary, EPP was established to have certain protective effects in T. sinensis infected with TSHSV. Specifically, EPP can effectively inhibit TSHSV proliferation and modulate the immune function of T. sinensis, thereby indicating its potential application as a means of preventing TSHSV. Our findings in this study will provide an important basis for the development of drugs to prevent TSHSV.
