Detection of Tembusu Virus in Waterfowl Farms
Tembusu virus (TMUV) belongs to the genus Flavivirus of the family Flaviviridae and was first identified from Culex mosquitoes in Malaysia in 1955. In 2000, a chicken-origined TMUV strain was isolated in Malaysia and it could cause encephalitis and retarded growth in broiler chicks. Since 2010, an epidemic of severe egg drop syndrome caused by a variant TMUV, duck TMUV, has been reported on either egg-laying farms or breeder duck farms in China. The disease caused by the duck TMUV has spread to duck farms in Malaysia and Thailand. In addition to the severe egg drop syndrome, the duck TMUV causes decreased appetite, depression, retarded growth, diarrhea and neurological dysfunction. The infection may give a morbidity rate of 90%–100% and a mortality rate of 10%–30%. Previous reports demonstrate that the duck TMUV also causes similar clinical symptoms in chickens and geese and that the virus has also been isolated from mosquitoes, pigeons and sparrows. In 2019, a novel TMUV, strain TP1906, was identified from Culex mosquitoes in Taiwan. Concurrently with the discovery of mosquito-derived TP1906, a TMUV was identified from a diseased duck flock in Taiwan in the same year. In the present report, we describe the establishment of RT-PCR, nested RT-PCR and real-time RT-PCR for detecting of nucleic acids of TMUV with the detection limit of 1,000 copies, 100 copies and 20 copies, respectively. We also describe the clinical manifestation of the TMUV-infected ducks and geese and characteristics of the TMUV strain.
Identification of a common conformational epitope on the glycoprotein E2 of classical swine fever virus and border disease virus
Classical swine fever virus (CSFV) shares high structural and antigenic homology with bovine viral diarrhea virus (BVDV) and border disease virus (BDV). Because all three viruses can infect swine and elicit cross-reactive antibodies, it is necessary to differentiate among them with regard to serological diagnosis of classical swine fever. To understand the mechanism of crossreactivity, it is important to define common or specific epitopes of these viruses. For this purpose, epitope mapping of six monoclonal antibodies (mAbs) was performed using recombinant expressed antigenic domains of CSFV and BDV E2 proteins. One CSFV-specific conformational epitope and one CSFV and BDV common epitope within domain B/C of E2 were identified. Site-directed mutagenesis confirmed that residues G725 and V738/I738 of the CSFV-specific epitope and P709/L709 and E713 of the second epitope are important for mAbs binding. 3D structural modeling suggested that both epitopes are exposed on the surface of E2. These findings will further enhance the understanding of the structural and antigenic topography of glycoprotein E2 and will improve the differential diagnosis of porcine pestivirus infections.