Syncytial and Congregative Effects of Dengue and Zika Viruses on the Aedes Albopictus Cell Line Differ among Viral Strains

Abstract

Objective: Dengue viruses (DENV) and Zika virus (ZIKV) are transmitted among humans, or from non-human primates to humans, through mosquito bites. The interaction of the virus with mosquito cells is a key step in the viral life cycle. Therefore, the objective of this study was to determine how DENV and ZIKV interact with mosquito cells. Methods: Immunofluorescence assays and a direct visualization system were combined to monitor the syncytial or congregative effects of DENV and ZIKV strains on C6/36 cells. We examined the cytopathic effects of the strains on C6/36 mosquito cells, a widely used laboratory model for studying infection with these viruses. Results: Our results indicated that all strains of DENV-1 and DENV-2, most DENV-4 strains, and some DENV-3 strains caused syncytial effects on C6/36 cells, whereas some DENV-3 and DENV-4 strains, and all tested ZIKV strains, caused cell congregation after infection but no cell fusion. In addition, we detected a range of environmental pH values from 6.0 to 8.0 supporting virus-induced cell fusion. The optimal pH condition was 7.5, at which viral production was also highest. Furthermore, the UV-inactivated virus did not cause cell fusion, thus suggesting that viral replication may be required for DENV’s syncytial effects on C6/36 cells. Conclusion: Syncytial and congregative effects of DENV and ZIKV on Aedes albopictus cells differ among viral strains. Syncytial effects of DENV on C6/36 are important for viral replication.