Development of a live attenuated vaccine candidate against duck Tembusu viral disease

•We passage the DTMUV isolate FX2010 serially in chicken embryo fibroblasts.•We develop FX2010-180P as a live attenuated vaccine candidate.•The attenuation of FX2010-180P is due to 34 nucleotide changes.•FX2010-180P elicits good immune responses in ducks.•FX2010-180P is a promising candidate live vaccine against duck Tembusu viral disease.

Duck Tembusu virus (DTMUV) is a newly emerging pathogenic flavivirus that is causing massive economic loss in the Chinese duck industry. To obtain a live vaccine candidate against the disease, the DTMUV isolate FX2010 was passaged serially in chicken embryo fibroblasts (CEFs). Characterization of FX2010-180P revealed that it was unable to replicate efficiently in chicken embryonated eggs, nor intranasally infect mice or shelducks at high doses of 5.5 log10 tissue culture infectious doses (TCID50). FX2010-180P did not induce clinical symptoms, or pathological lesions in ducks at a dose of 5.5 log10 TCID50. The attenuation of FX2010-180P was due to 19 amino acid changes and 15 synonymous mutations. Importantly, FX2010-180P elicited good immune responses in ducks inoculated at low doses (3.5 log10 TCID50) and provided complete protection against challenge with a virulent strain. These results indicate that FX2010-180P is a promising candidate live vaccine for prevention of duck Tembusu viral disease.