Efficacy assessment of an inactivated Tembusu virus vaccine candidate in ducks.

Duck Tembusu virus (TMUV) is a recently identified pathogen that causes severe egg drop and neurological disease in domestic duck and goose flocks. The infection has spread across the China mainland since its outbreak in 2010. Effective vaccines are needed to fight the disease. In this work, we describe the development and laboratory assessment of a cell culture-derived, inactivated duck TMUV vaccine. The TMUV-JXSP strain was successfully propagated on a baby hamster kidney cell line (BHK-21), inactivated with beta-propiolactone (BPL) and emulsified with mineral oil. The efficacy of different vaccination schedules was assessed in laying ducks and table ducks using virus challenge experiments. Two doses of vaccine provided efficient protection against the virus challenge to avoid the egg production drop in laying ducks. An ELISA demonstrated that 97% (39/40) of ducks seroconverted on day 21 after one dose of the inactivated vaccine and that significant increases in antibody titers against the virus were induced after the second immunization. For table ducks, a single dose of vaccine immunization resulted in a protection index of 87% and significant reduction of viral loads in tissues. Sterilizing immunity can be attained after second immunization. Our results demonstrate that BHK-21 cell culture is suitable for duck TMUV propagation and that BPL-inactivated TMUV vaccine can provide a high level of protection from virus challenge in laying ducks and table ducks. These data provide a scientific basis for the development of an inactivated vaccine for the prevention of duck TMUV infection.