Introduction

Insect-specific flaviviruses (ISF) only infect mosquitoes but appear to regulate the transmission of pathogenic viruses by their insect host (1, 2). Additional isolates of ISFs are required to characterise their phylogenetics, host restriction and transmission dynamics and elucidate mechanisms of interference with other viruses in the mosquito.

Methods

We screened mosquito samples from different locations in Australia for novel ISFs using an innovative, high-throughput, sequence-independent virus detection system. After inoculation of mosquito cell cultures with homogenised samples, positive-strand RNA viruses were detected in ELISA via the presence of viral dsRNA replicative intermediates in inoculated cells (3). RNA extracted from positive cultures was tested by generic flavivirus RT-PCR to identify new ISFs (4). Next generation sequencing, monoclonal antibodies binding assays and growth kinetics in different cell lines was undertaken to characterise these novel viruses.

Results

A new flavivirus, Bamaga virus (BgV), was isolated from Culex annulirostris collected from Cape York in 2001. Inoculation of simian and rodent cell lines revealed that vertebrate cells were poorly susceptible to BgV infection, indicative of an ISF. However, phylogenetic analysis of the RNA genome sequence of BgV grouped it with flaviviruses known to infect vertebrates, and separately from other ISF species (5). BgV was shown to be genetically and antigenically most closely related to Edge Hill, yellow fever and dengue viruses (6).

Conclusion

BgV represents a new genetic lineage of ISF that may have recently adapted to a mosquito only transmission cycle and may serve as a useful model to study the biology of ISFs, their interaction with the host mosquito and their evolution.

References