Roles of BALB/c mice and Aedes mosquitoes in the transmission of duck Tembusu virus

Abstract

Duck Tembusu virus (DTMUV) is an emerging flavivirus that causes severe nervous and systemic diseases in avian hosts. The virus has been classified into three clusters, and the predominant cluster in Thailand is cluster 2.1. The pathogenesis of the virus has been extensively studied in avian hosts but not in mammalian hosts. Therefore, the first objective of this dissertation was to investigate the viral pathogenesis in mammalian hosts. Six-week-old BALB/c mice were intracerebrally and subcutaneously inoculated with Thai DTMUV to examine clinical signs, pathological change, viral load, and virus distribution. Results demonstrated that Thai DTMUV caused an acute severe disease, and it was a cause of death in BALB/c mice inoculated by the intracerebral route. Infected mice showed both systemic and neurological symptoms. Pathological changes and virus distribution were observed in all tested organs. Viral load in the brain was significantly higher than in other organs (p<0.05). However, virus shedding was not recorded in saliva and feces. The findings suggested that Thai DTMUV has the potential to cause the threatening disease in mammalian hosts. In addition, one of the virus transmission routes is mosquito bites, but the interaction between Thai DTMUV and Aedes (Ae.) mosquito, which is a mammalian host preferred-mosquito, is lacking. Thus, the second objective was to examine the vector competence of Ae. aegypti and Ae. albopictus mosquitoes for Thai DTMUV. Results indicated that both Aedes mosquito species could serve as vectors for Thai DTMUV with minimum viral titer in a blood meal of 106 TCID50/mL. When Aedes mosquitoes received more viral titer (107 TCID50/mL), their competence significantly increased (p<0.05). In contrast, both Aedes species did not support the development of the isolated Thai DTMUV viruses from BALB/c mice because their titer was less than 106 TCID50/mL. The third objective was to investigate the viral genomes that were isolated from BALB/c mice, Ae. aegypti, and Ae. albopictus mosquitoes compared with the original virus. A point mutation of nucleotide and the amino acid was found in all isolated DTMUV from Ae. aegypti saliva, while other viruses were similar to the positive virus. In summary, our results provide important information about Thai DTMUV in mammalian hosts, mosquito vectors, and virus genome that were useful for preventing and controlling the disease in both avian and mammalian hosts.