Genetic, Morphological and Antigenic Relationships between Mesonivirus Isolates from Australian Mosquitoes and Evidence for Their Horizontal Transmission

Abstract

The Mesoniviridae are a newly assigned family of viruses in the order Nidovirales. Unlike other nidoviruses, which include the Coronaviridae, mesoniviruses are restricted to mosquito hosts and do not infect vertebrate cells. To date there is little information on the morphological and antigenic characteristics of this new group of viruses and a dearth of mesonivirus-specific research tools. In this study we determined the genetic relationships of recent Australian isolates of Alphamesonivirus 4 (Casuarina virus—CASV) and Alphamesonivirus 1 (Nam Dinh virus—NDiV), obtained from multiple mosquito species. Australian isolates of NDiV showed high-level similarity to the prototype NDiV isolate from Vietnam (99% nucleotide (nt) and amino acid (aa) identity). Isolates of CASV from Central Queensland were genetically very similar to the prototype virus from Darwin (95–96% nt and 91–92% aa identity). Electron microscopy studies demonstrated that virion diameter (≈80 nm) and spike length (≈10 nm) were similar for both viruses. Monoclonal antibodies specific to CASV and NDiV revealed a close antigenic relationship between the two viruses with 13/34 mAbs recognising both viruses. We also detected NDiV RNA on honey-soaked nucleic acid preservation cards fed on by wild mosquitoes supporting a possible mechanism of horizontal transmission between insects in nature.

Uncovering the genetic diversity within the Aedes notoscriptus virome and isolation of new viruses from this highly urbanised and invasive mosquito

“…Based on the results described herein and previous isolation of RRV ( Ritchie et al., 1997 ), Edge Hill virus ( Doggett et al., 2017 ), BFV ( Doggett et al., 2011 ), STRV ( Toi et al., 2017 ), Sindbis virus ( Broom et al., 2002 ), and Nam Dinh virus ( Newton et al., 2020 ), Ae. notoscriptus appears to harbour a genetically diverse virome.…”

“…For example, both honey bees and mosquitoes consume floral nectaries ( Foster 1995 ; Berenbaum and Calla 2021 ). Therefore, it is plausible that transmission may occur via exposure to virus-infected nectar, similar to that suggested by Newton et al., (2020) for mesoniviruses. Furthermore, it is also possible that each of these viruses have an even broader host range than the respective mosquito, bee, and mite species they were first isolated from, in which case, additional modes of transmission may also be involved.…”

“…vigilax and Cx. annulirostris mosquitoes ( Newton et al., 2020 ). With so few isolates, it is difficult to infer if seeding of CASV from the NT into QLD has occurred, although there appears a tentative relationship between the Brisbane isolates and the NT 2010 prototype strain, with the latter positioned basally relative to the Brisbane viruses within the phylogenetic trees.…”

“…We further performed Bayesian phylogenetics (as described for STRV above) to compare the near-complete genome sequence (19,923 nucleotides) of Casuarina virus (CASV) isolate 205089, with other available CASV isolates including the prototype 2010 Darwin, Northern Territory (NT), Australia 0071 isolate and isolates collected from the military Shoalwater Bay Training Area (SWBTA) in QLD, Australia in 2019, namely, SWBTA-Mes-ann from Culex annulirostris mosquitoes and SWBTA-Mes-vigilax from Aedes vigilax mosquitoes (GenBank accession numbers MT522182 and MT522183 , respectively). The sequence of a third CASV SWBTA isolate (GenBank accession number MT522184 ) obtained from Aedes procax mosquitoes ( Newton et al., 2020 ) was not included in our analysis due to the presence of a large number of ambiguous bases.…”

Readdressing the genetic diversity and taxonomy of the Mesoniviridae family, as well as its relationships with other nidoviruses and putative mesonivirus-like viral sequences

“…KPhV and BBaV are both assigned as members of the Alphamesonivirus 1/AMV1 species and of the Namcalivirus subgenus in NCBI's taxonomy browser (Schoch et al, 2020), which would mean, by the obtained tree topology, that namcaliviruses are paraphyletic. However, previous studies never did place KPhV and BBaV into that specific Alphamesonivirus species (Vasilakis et al, 2014;Wang et al, 2017;Newton et al, 2020), with Vasilakis et al (2014) even suggesting, by PED analysis, that these two species should be considered as separate species. Indeed, our analysis did confirm this.…”