Attenuation of duck Tembusu virus ZJSBL01 strain following serial passage in BHK-21 cells supplied with 5-Fluorouracil.

Duck Tembusu virus (DTMUV) is a new pathogen that produces an acute and potent disease in ducks which has caused serious economic losses in China. In this study, a virulent strain of DTMUV, designated as ZJSBL01, was attenuated by serial passages in BHK-21 cells supplied with 5-Fluorouracil (5-FU) for 50 passages to induce mutation and attenuation. Growth kinetics of different passages of ZJSBL01 strain in BHK-21 cells show that these viruses have similar replication characteristics. The virus was highly attenuated after 40 passages in BHK-21 cells supplied with 5-FU, based on mortality, morbidity, and viral load in inoculated Sheldrake ducklings. In addition, all of the ducklings immunized with ZJSBL01-P40, the virus obtained at passage 40 of ZJSBL01, showed seroconversion on day 14 post inoculation. Moreover, P40 did not cause clinical symptom for layding ducks. Immunization with ZJSBL01-P40 could provide effective protection against the virulent parental ZJSBL01 strain. Seventeen amino acid substitutions were observed in the polyprotein of ZJSBL01-P40 compared with parental ZJSBL01. These results indicate that ZJSBL01-P40 may be a live vaccine candidate for prevention of DTMUV-disease.