Abstract
BackgroundInsect-specific viruses do not replicate in vertebrate cells, but persist in mosquito populations and are highly prevalent in nature. These viruses may naturally regulate the transmission of pathogenic vertebrate-infecting arboviruses in co-infected mosquitoes. Following the isolation of the first Australian insect-specific flavivirus (ISF), Palm Creek virus (PCV), we investigated routes of infection and transmission of this virus in key Australian arbovirus vectors and its impact on replication and transmission of West Nile virus (WNV).MethodsCulex annulirostris, Aedes aegypti and Aedes vigilax were exposed to PCV, and infection, replication and transmission rates in individual mosquitoes determined. To test whether the virus could be transmitted vertically, progeny reared from eggs oviposited by PCV-inoculated Cx. annulirostris were analysed for the presence of PCV. To assess whether prior infection of mosquitoes with PCV could also suppress the transmission of pathogenic flaviviruses, PCV positive or negative Cx. annulirostris were subsequently exposed to WNV.ResultsNo PCV-infected Cx. annulirostris were detected 16 days after feeding on an infectious blood meal. However, when intrathoracically inoculated with PCV, Cx. annulirostris infection rates were 100 %. Similar rates of infection were observed in Ae. aegypti (100 %) and Ae. vigilax (95 %). Notably, PCV was not detected in any saliva expectorates collected from any of these species. PCV was not detected in 1038 progeny reared from 59 PCV-infected Cx. annulirostris. After feeding on a blood meal containing 107 infectious units of WNV, significantly fewer PCV-infected Cx. annulirostris were infected or transmitted WNV compared to PCV negative mosquitoes. Immunohistochemistry revealed that PCV localized in the midgut epithelial cells, which are the first site of infection with WNV.ConclusionsOur results indicate that PCV cannot infect Cx. annulirostris via the oral route, nor be transmitted in saliva or vertically to progeny. We also provide further evidence that prior infection with insect-specific viruses can regulate the infection and transmission of pathogenic arboviruses.
Highlights
Insect-specific viruses do not replicate in vertebrate cells, but persist in mosquito populations and are highly prevalent in nature
The results of our experiments are consistent with previous studies that show prior infection of Culex mosquitoes with the insect-specific flaviviruses Culex flavivirus (CxFV) or Nhumirim virus, significantly suppressed or delayed West Nile virus (WNV) transmission by some species [3, 6]
Future studies should investigate whether prior infection with Aedes insect-specific flavivirus (ISF) such as CFAV, Kamiti River virus or another Australian ISF, Parramatta River virus (PaRV) [7, 30, 31], have a similar effect on the transmission of dengue viruses (DENVs) and Zika virus (ZIKV) by Ae. aegypti and/or Ae. albopictus, which are the primary vectors of these pathogenic flaviviruses
Summary
Insect-specific viruses do not replicate in vertebrate cells, but persist in mosquito populations and are highly prevalent in nature. Insect-specific flaviviruses (ISFs) have been isolated from numerous species of mosquitoes from different genera, and from most regions of the world (reviewed in [1]) These flaviviruses differ from medically important members of the genus, such as West Nile virus (WNV), dengue. Palm Creek virus (PCV) was the first ISF to be discovered in Australia, where it was isolated from Coquillettidia xanthogaster mosquitoes, captured from northern Australia [4, 7] This mosquito species is susceptible to infection with WNV and Ross River virus (RRV), a prevalent alphavirus in Australia, it is not considered to be a major arbovirus vector [8, 9]. Similar findings have subsequently been reported for other ISFs [5]
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