First Report of a Mesonivirus and Its Derived Small RNAs in an Aphid Species Aphis citricidus (Hemiptera: Aphididae), Implying Viral Infection Activity.

We report a new positive-sense single-stranded RNA (ss RNA+) virus from the brown citrus aphid Aphis citricidus. The 20,300 nucleotide (nt)-long viral genome contains five open-reading frames and encodes six conserved domains (TM2, 3CLpro, TM3, RdRp, Zm, and HEL1). Phylogenetic analysis and amino acid sequence analysis revealed this virus might belong to an unassigned genus in the family Mesoniviridae. The presence of the virus was also confirmed in the field population. Importantly, analysis of the virus-derived small RNAs showed a 22-nt peak, implying that viral infection triggers the small interfering RNA pathway as antiviral immunity in aphids. This is the first report of a mesonivirus in invertebrates other than mosquitoes.

Interaction of Mesonivirus and Negevirus with arboviruses and the RNAi response in Culex tarsalis-derived cells.

BACKGROUND: Mosquito-specific viruses (MSVs) comprise a variety of different virus families, some of which are known to interfere with infections of medically important arboviruses. Viruses belonging to the family Mesoniviridae or taxon Negevirus harbor several insect-specific viruses, including MSVs, which are known for their wide geographical distribution and extensive host ranges. Although these viruses are regularly identified in mosquitoes all over the world, their presence in mosquitoes in Germany had not yet been reported. METHODS: A mix of three MSVs (Yichang virus [Mesoniviridae] and two negeviruses [Daeseongdong virus and Dezidougou virus]) in a sample that contained a pool of Coquillettidia richiardii mosquitoes collected in Germany was used to investigate the interaction of these viruses with different arboviruses in Culex-derived cells. In addition, small RNA sequencing and analysis of different mosquito-derived cells infected with this MSV mix were performed. RESULTS: A strain of Yichang virus (Mesoniviridae) and two negeviruses (Daeseongdong virus and Dezidougou virus) were identified in the Cq. richiardii mosquitoes sampled in Germany, expanding current knowledge of their circulation in central Europe. Infection of mosquito-derived cells with these three viruses revealed that they are targeted by the small interfering RNA (siRNA) pathway. In Culex-derived cells, co-infection by these three viruses had varying effects on the representative arboviruses from different virus families (Togaviridae: Semliki forest virus [SFV]; Bunyavirales: Bunyamwera orthobunyavirus [BUNV]; or Flaviviridae: Usutu virus [USUV]). Specifically, persistent MSV co-infection inhibited BUNV infection, as well as USUV infection (but the latter only at specific time points). However, the impact on SFV infection was only noticeable at low multiplicity of infection (MOI 0.1) and at specific time points in combination with the infection status. CONCLUSIONS: Taken together, these results are important findings that will lead to a better understanding of the complex interactions of MSVs, mosquitoes and arboviruses.

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

Research on the recently established Mesoniviridae family (Order Nidovirales), RNA genome insect-specific viruses, has been steadily growing in the last decade. However, after the last detailed phylogenetic characterization of mesoniviruses in 2014, numerous new sequences, even in organisms other than mosquitos, have been identified and characterized. In this study, we analyzed nucleotide and protein sequences of mesoniviruses with a wide range of molecular tools including genetic distance, Shannon entropy, selective pressure analysis, polymorphism identification, principal coordinate analysis, likelihood mapping and phylodynamic reconstruction. We also sought to revaluate new mesoniviruses sequence positions within the family, proposing a taxonomic revision. The different sub-lineages of mosquito mesoniviruses sequences presented low sequence diversity and entropy, with incongruences to the existing taxonomy being found after an extensive phylogenetic characterization. High sequence discrepancy and differences in genome organization were found between mosquito mesoniviruses and other mesoniviruses, so their future classification, as other meso-like viruses that are found in other organisms, should be approached with caution. No evidence of frequent recombination was found, and mesonivirus genomes seem to evolve under strong purifying selection. Insufficient data by root-to-tip analysis did not yet allow for an adequate phylogeographic reconstruction.

Aphid Viruses: A Brief View of a Long History.

Aphids are common agricultural pests with a wide range of hosts from agriculture to forestry plants. As known, aphids also serve as the major vectors to transmit plant viruses. Although numerous studies have focused on interactions between aphids and plant viruses, little is known about the aphid viruses, i.e., the insect viruses that are infectious to aphids. In the past four decades, several aphid viruses have been identified in diverse aphid species. In this review, we present a brief view of the aphid pathogenic viruses from several aspects, including classification of aphid viruses and characters of the viral genome, integration of viral sequences in host genomes, infection symptoms and influence on aphids, as well as host range and transmission modes. Taken together, these studies have increased our understanding of the rarely known aphid viruses, and will potentially contribute to the development of new strategies for controlling aphid populations.

Dianke virus: A new mesonivirus species isolated from mosquitoes in Eastern Senegal.

An increasing number of insect-specific viruses are found around the world. Very recently, a new group of insect-specific viruses, the Mesoniviridae family, was discovered in Africa, Asia, North America and Australia. Here we report the first detection and isolation of a new virus belonging to Mesonivirus genus in Senegal, West Africa. The so-called Dianke virus was detected in 21 species of arthropods trapped in the eastern part of the country. Male individuals were also infected, supporting vertical transmission assertion of insect specific viruses. As described for other mesoniviruses, no viral replication was observed after inoculation of mammalian cells. Viral replication in mosquito cells was blocked at a temperature of 37 °C, highlighting the importance of thermal conditions in Mesonivirus host restriction. Similar to our study, where a diverse range of arthropod vectors were found infected by the new virus, several studies have detected mesonivirus infection in mosquitoes with concerns for human health. It has been shown that dual infections in mosquito can alter viral infectivity. Due to their extensive geographic distribution and host range, as well as their use as potential disease control agents in vector populations, more studies should be done for a better knowledge of arthropod-restricted viruses prevalence and diversity.

Mosquito-borne viruses, insect-specific flaviviruses (family Flaviviridae, genus Flavivirus), Banna virus (family Reoviridae, genus Seadornavirus), Bogor virus (unassigned member of family Permutotetraviridae), and alphamesoniviruses 2 and 3 (family Mesoniviridae, genus Alphamesonivirus) isolated from Indonesian mosquitoes.

Mosquitoes transmit many kinds of arboviruses (arthropod-borne viruses), and numerous arboviral diseases have become serious problems in Indonesia. In this study, we conducted surveillance of mosquito-borne viruses at several sites in Indonesia during 2016-2018 for risk assessment of arbovirus infection and analysis of virus biodiversity in mosquito populations. We collected 10,015 mosquitoes comprising at least 11 species from 4 genera. Major collected mosquito species were Culex quinquefasciatus, Aedes albopictus, Culex tritaeniorhynchus, Aedes aegypti, and Armigeres subalbatus. The collected mosquitoes were divided into 285 pools and used for virus isolation using two mammalian cell lines, Vero and BHK-21, and one mosquito cell line, C6/36. Seventy-two pools showed clear cytopathic effects only in C6/36 cells. Using RT-PCR and next-generation sequencing approaches, these isolates were identified as insect flaviviruses (family Flaviviridae, genus Flavivirus), Banna virus (family Reoviridae, genus Seadornavirus), new permutotetravirus (designed as Bogor virus) (family Permutotetraviridae, genus Alphapermutotetravirus), and alphamesoniviruses 2 and 3 (family Mesoniviridae, genus Alphamesonivirus). We believed that this large surveillance of mosquitoes and mosquito-borne viruses provides basic information for the prevention and control of emerging and re-emerging arboviral diseases.

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

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.

Structural basis for catalysis and substrate specificity of a 3C-like cysteine protease from a mosquito mesonivirus.

Cavally virus (CavV) is a mosquito-borne plus-strand RNA virus in the family Mesoniviridae (order Nidovirales). We present X-ray structures for the CavV 3C-like protease (3CLpro), as a free enzyme and in complex with a peptide aldehyde inhibitor mimicking the P4-to-P1 residues of a natural substrate. The 3CLpro structure (refined to 1.94 Å) shows that the protein forms dimers. The monomers are comprised of N-terminal domains I and II, which adopt a chymotrypsin-like fold, and a C-terminal α-helical domain III. The catalytic Cys-His dyad is assisted by a complex network of interactions involving a water molecule that mediates polar contacts between the catalytic His and a conserved Asp located in the domain II-III junction and is suitably positioned to stabilize the developing positive charge of the catalytic His in the transition state during catalysis. The study also reveals the structural basis for the distinct P2 Asn-specific substrate-binding pocket of mesonivirus 3CLpros.

The Interaction between Nidovirales and Autophagy Components.

Autophagy is a conserved intracellular catabolic pathway that allows cells to maintain homeostasis through the degradation of deleterious components via specialized double-membrane vesicles called autophagosomes. During the past decades, it has been revealed that numerous pathogens, including viruses, usurp autophagy in order to promote their propagation. Nidovirales are an order of enveloped viruses with large single-stranded positive RNA genomes. Four virus families (Arterividae, Coronaviridae, Mesoniviridae, and Roniviridae) are part of this order, which comprises several human and animal pathogens of medical and veterinary importance. In host cells, Nidovirales induce membrane rearrangements including autophagosome formation. The relevance and putative mechanism of autophagy usurpation, however, remain largely elusive. Here, we review the current knowledge about the possible interplay between Nidovirales and autophagy.