A Single Mutation at Position 156 in the Envelope Protein of Tembusu Virus Is Responsible for Virus Tissue Tropism and Transmissibility in Ducks.

Duck Tembusu virus (TMUV), like other mosquito-borne flaviviruses, such as Japanese encephalitis virus, West Nile virus, and Bagaza virus, is able to transmit vector-independently. To date, why these flaviviruses can be transmitted without mosquito vectors remains poorly understood. To explore the key molecular basis of flavivirus transmissibility, we compared virus replication and transmissibility of an early and a recent TMUV in ducks. The recent TMUV strain FX2010 replicated systemically and transmitted efficiently in ducks, while the replication of early strain MM1775 was limited and did not transmit among ducks. The TMUV envelope protein and its domain I were responsible for tissue tropism and transmissibility. The mutation S156P in the domain I resulted in disruption of N-linked glycosylation at amino acid 154 of the E protein and changed the conformation of "150 loop" of the E protein, which reduced virus replication in lungs and abrogated transmission in ducks. These data indicate that the 156S in the envelope protein is critical for TMUV tissue tropism and transmissibility in ducks in the absence of mosquitos. Our findings provide novel insights on understanding TMUV transmission among ducks.IMPORTANCE Tembusu virus, similar to other mosquito-borne flaviviruses such as WNV, JEV, and BAGV, can be transmitted without the presence of mosquito vectors. We demonstrate that the envelope protein of TMUV and its amino acid (S) at position 156 is responsible for tissue tropism and transmission in ducks. The mutation S156P results in disruption of N-linked glycosylation at amino acid 154 of the E protein and changes the conformation of "150 loop" of the E protein, which induces limited virus replication in lungs and abrogates transmission between ducks. Our findings provide new knowledge about TMUV transmission among ducks.