# New Insights into the Biology of the Emerging Tembusu Virus
## 4 Clinical Features and Pathogenicity
### Treatment and Vaccine Development  
As with some other flavivirus infections, there is no specific treatment for TMUV. The antiviral efficacy of different molecules is currently being evaluated. For example, minocycline, a tetracycline analogue, has shown some efficiency in vitro against neuronal cell death infected by neurotrophic viruses. This neuroprotective effect was also found with duck neuronal cells infected with TMUV [128]. Epigallocatechin-3-gallate (EGCG), a polyphenol-like active molecule, has already shown broad-spectrum activity against different viruses and appears as a promising treatment against TMUV infection. EGCG use in BHK-21 cells showed a significant decrease in TMUV replication, probably due to an increase in type I IFN production. This effect was then confirmed by an increased survival rate of TMUV-infected ducklings treated with EGCG [129]. New therapeutic strategies are being evaluated to prevent or directly treat TMUV. The use of the capsid-targeted viral inactivation (CTVI) strategy, an antiviral strategy targeting the capsid protein originally developed to target retroviruses [130] and which has shown success against DENV and JEV [131; 132], has also been recently evaluated for the treatment of TMUV [133]. Currently, there is no commercial vaccine against TMUV. However, regarding the large spread of the virus in Asia since the first outbreak in China in 2010 and the association with a high economic impact on the poultry industry, the development of an effective vaccine is a primary objective. Since the first report of the virus, different research teams have taken on the challenge. In China, attenuated viruses by passaging in embryonated chicken eggs were developed as a live vaccine strategy [134; 135]. The attenuation of virulence might be due to amino acid substitution in structural and nonstructural proteins, but the attenuated viruses keep their immunogenicity, thereby providing effective protection for animals against TMUV infection. Different types of oil emulsion-containing inactivated TMUV vaccines were developed to protect ducks against TMUV [136]. In 2017, [PERSON] et al. proposed using an inactivated TMUV from the TMUV-JXSP strain which was successfully propagated in the BHK-21 cell line, then inactivated using \(\beta\)-propiolactone and associated with medical-grade white oil to obtain an oil emulsion vaccine amenable for injection. Vaccinated ducks presented an increase in antibody titers after the first injection and experienced a diminution of viral load without apparition of the egg drop effect [137]. In the same way, after several passages of TMUV isolated from sparrows in China, attenuated viruses possessed a strong immunogenicity and provided an effective protection for ducks exposed to TMUV [138]. Recently, the team of [PERSON] et al. worked with a variant of TMUV which developed attenuated virulence after several passages. Their work shed new light on the development of an effective vaccine against TMUV infection, determining that residue 304 of the E protein was essential for virulence and cell attachment [139]. However, despite the interest of these candidate vaccines, further investigations are needed to optimize certain aspects of vaccination such as the route of inoculation, the optimal number of inoculations to achieve the correct immunity or possible interactions with other animal vaccination programs. Two recombinant duck enteritis viruses were also designed to express a part of the TMUV E protein and the pre-membrane protein. Immunization of ducks led to the production of protective neutralizing antibodies, and further TMUV-challenged animals exhibited resistance to the infection [140]. A reverse genetic strategy was used to produce a chimeric recombinant TMUV based on the JEV backbone, which was successfully used in mice [141]. In 2016, [PERSON] et al. used liposomes containing a recombinant TMUV E protein produced in BL21 cells to immunize ducks.