In vitro comparison of three common essential oils mosquito repellents as inhibitors of the Ross River virus.

BACKGROUND: The essential oils of Cymbopogon citratus (CC), Pelargonium graveolens (PG) and Vetiveria zizanioides (VZ) are commonly used topically to prevent mosquito bites and thus the risk of infection by their vectored pathogens such as arboviruses. However, since mosquito bites are not fully prevented, the effect of these products on the level of viral infection remains unknown. OBJECTIVES: To evaluate in vitro the essentials oils from Reunion Island against one archetypal arbovirus, the Ross River virus (RRV), and investigate the viral cycle step that was impaired by these oils. METHODS: The essential oils were extracted by hydrodistillation and analyzed by a combination of GC-FID and GC×GC-TOF MS techniques. In vitro studies were performed on HEK293T cells to determine their cytotoxicity, their cytoprotective and virucidal capacities on RRV-T48 strain, and the level of their inhibitory effect on the viral replication and residual infectivity prior, during or following viral adsorption using the reporter virus RRV-renLuc. RESULTS: Each essential oil was characterized by an accurate quantification of their terpenoid content. PG yielded the least-toxic extract (CC50 > 1000 µg.mL-1). For the RRV-T48 strain, the monoterpene-rich CC and PG essential oils reduced the cytopathic effect but did not display virucidal activity. The time-of-addition assay using the gene reporter RRV-renLuc showed that the CC and PG essential oils significantly reduced viral replication and infectivity when applied prior, during and early after viral adsorption. Overall, no significant effect was observed for the low monoterpene-containing VZ essential oil. CONCLUSION: The inhibitory profiles of the three essential oils suggest the high value of the monoterpene-rich essential oils from CC and PG against RRV infection. Combined with their repellent activity, the antiviral activity of the essential oils of CC and PG may provide a new option to control arboviral infection.

The growth of arthralgic Ross River virus is restricted in human monocytic cells.

Alphaviruses such as Chikungunya and Ross River (RRV) viruses are associated with persistent arthritis and arthralgia in humans. Monocytes and macrophages are believed to play an important role in alphaviral arthritides. In this study, we evaluated RRV permissiveness of the human acute leukemia MM6 cell line. Viral growth analysis showed that RRV infection of MM6 cells resulted in a very low virus progeny production with daily output. Using recombinant RRV expressing the reporter gene Renilla luciferase, a weak viral replication level was detected in infected cells at the early stages of infection. The infection restriction was not associated with type-I interferon and pro-inflammatory cytokines release. Apoptosis hallmarks (i.e. mitochondrial BAX localisation and PARP cleavage) were observed in infected MM6 cells indicating that RRV can trigger apoptosis at late infection times. The long-term persistence of RRV genomic RNA in surviving MM6 cells identifies human monocytic cells as potential cellular reservoirs of viral material within the infected host.