Effect of Wolbachia wAlbB on a positive-sense RNA negev-like virus: a novel virus persistently infecting Aedes albopictus mosquitoes and cells.

The Aedes aegypti mosquito is the primary vector of several medically important arboviruses. The endosymbiotic bacterium, Wolbachia pipientis, has emerged as a means of blocking transmission of arboviruses such as dengue and Zika viruses. One Wolbachia strain that has shown potential in field trials is wAlbB, a naturally occurring Wolbachia strain of the Asian tiger mosquito Aedes albopictus. When transinfected into Ae. aegypti, wAlbB exhibits strong virus inhibition. In addition to modulating arboviruses, Wolbachia also modulates some insect-specific viruses. Here, we explored the effect of Wolbachia on the virome of the Ae. albopictus cell line Aa23 naturally infected with wAlbB and also a stably transinfected recipient Ae. aegypti cell line (Aag2.wAlbB). RNA sequencing and bioinformatic analysis on both cell lines revealed an 11 kb genome of a single-stranded positive-sense RNA negev-like virus related to the recently proposed negevirus taxon. We denoted this novel virus as Aedes albopictus negev-like virus (AalNLV). Tetracycline clearance of Wolbachia from Aa23 cells did not significantly affect AalNLV levels, while in Aag2.wAlbB cells, a significant increase in virus genome RNA copies was observed. We further investigated the inhibitory effect of wAlbB on AalNLV and another positive-sense RNA virus, cell fusing agent virus, which is present in Aag2 cells and known to be suppressed by Wolbachia. wAlbB suppressed both viruses, with the effect on AalNLV being more striking. The findings from this study further supplement our understanding of the complex interaction between Wolbachia, host and virome.

Nutritional demands and metabolic characteristics of the DSIR-HA-1179 insect cell line during growth and infection with the Oryctes nudivirus.

The DSIR-HA-1179 coleopteran cell line has been identified as a susceptible and permissive host for the in vitro replication of the Oryctes nudivirus, which can be used as a biopesticide against the coconut rhinoceros beetle, pest of palms. The major challenge to in vitro large-scale Oryctes nudivirus production is ensuring process economy. This rests, among other requisites, on the use of low-cost culture media tailored to the nutritional and metabolic needs of the cell line, both in uninfected and infected cultures. The aim of the present study was to characterize the nutritional demands and the metabolic characteristics of the DSIR-HA-1179 cell line during growth and subsequent infection with Oryctes nudivirus in the TC-100 culture medium. Serum-supplementation of the culture medium was found to be critical for cell growth, and addition of 10% fetal bovine serum v/v led to a maximum viable cell density (16.8 × 105 cells ml-1) with a population doubling time of 4.2 d. Nutritional and metabolic characterization of the cell line revealed a trend of glucose and glutamine consumption but minimal uptake of other amino acids, negligible production of lactate and ammonia, and the accumulation of alanine, both before and after infection. The monitoring of virus production kinetics showed that the TC-100 culture medium was nutritionally sufficient to give a peak yield of 7.38 × 107 TCID50 ml-1 of OrNV at the 6th day post-infection in attached cultures of DSIR-HA-1179 cells in 25 cm2 T-flasks. Knowledge of the cell line's nutritional demands and virus production kinetics will aid in the formulation of a low-cost culture medium and better process design for large-scale OrNV production in future.

Utilization of an Eilat Virus-Based Chimera for Serological Detection of Chikungunya Infection.

In December of 2013, chikungunya virus (CHIKV), an alphavirus in the family Togaviridae, was introduced to the island of Saint Martin in the Caribbean, resulting in the first autochthonous cases reported in the Americas. As of January 2015, local and imported CHIKV has been reported in 50 American countries with over 1.1 million suspected cases. CHIKV causes a severe arthralgic disease for which there are no approved vaccines or therapeutics. Furthermore, the lack of a commercially available, sensitive, and affordable diagnostic assay limits surveillance and control efforts. To address this issue, we utilized an insect-specific alphavirus, Eilat virus (EILV), to develop a diagnostic antigen that does not require biosafety containment facilities to produce. We demonstrated that EILV/CHIKV replicates to high titers in insect cells and can be applied directly in enzyme-linked immunosorbent assays without inactivation, resulting in highly sensitive detection of recent and past CHIKV infection, and outperforming traditional antigen preparations.

Proteomic analysis of the occlusion-derived virus of Clostera anachoreta granulovirus.

To date, proteomic studies have been performed on occlusion-derived viruses (ODVs) from five members of the family Baculoviridae, genus Alphabaculovirus, but only a single member of the genus Betabaculovirus (Pieris rapae granulovirus). In this study, LC-MS/MS was used to analyse the ODV proteins of Clostera anachoreta granulovirus (ClanGV), another member of the genus Betabaculovirus. The results indicated that 73 proteins, including the products of 27 baculovirus core genes, were present in ClanGV ODVs. This is the largest number of ODV proteins identified in baculoviruses to date. To the best of our knowledge, 24 of these proteins were newly identified as ODV-associated proteins. Twelve of the proteins were shared by all seven of the other baculoviruses that have been analysed by proteomic techniques, including P49, PIF-2, ODV-EC43, P74, P6.9, P33, VP39, ODV-EC27, VP91, GP41, VLF-1 and VP1054. ClanGV shared between 20 and 36 ODV proteins with each of the other six baculoviruses that have been analysed by proteomics. Ten proteins were identified only as ODV components of ClanGV and PrGV: Clan22, Clan27, Clan69, Clan83, Clan84, Clan90, Clan116, Clan94, FGF-3 and ME53, the first seven of which were encoded by betabaculovirus-specific genes. These findings may provide novel insights into baculovirus structure as well as reveal similarities and differences between alphabaculoviruses and betabaculoviruses.

Propagation of Homalodisca coagulata virus-01 via Homalodisca vitripennis cell culture.

The glassy-winged sharpshooter (Homalodisca vitripennis) is a highly vagile and polyphagous insect found throughout the southwestern United States. These insects are the predominant vectors of Xylella fastidiosa (X. fastidiosa), a xylem-limited bacterium that is the causal agent of Pierce's disease (PD) of grapevine. Pierce's disease is economically damaging; thus, H. vitripennis have become a target for pathogen management strategies. A dicistrovirus identified as Homalodisca coagulata virus-01 (HoCV-01) has been associated with an increased mortality in H. vitripennis populations. Because a host cell is required for HoCV-01 replication, cell culture provides a uniform environment for targeted replication that is logistically and economically valuable for biopesticide production. In this study, a system for large-scale propagation of H. vitripennis cells via tissue culture was developed, providing a viral replication mechanism. HoCV-01 was extracted from whole body insects and used to inoculate cultured H. vitripennis cells at varying levels. The culture medium was removed every 24 hr for 168 hr, RNA extracted and analyzed with qRT-PCR. Cells were stained with trypan blue and counted to quantify cell survivability using light microscopy. Whole virus particles were extracted up to 96 hr after infection, which was the time point determined to be before total cell culture collapse occurred. Cells were also subjected to fluorescent staining and viewed using confocal microscopy to investigate viral activity on F-actin attachment and nuclei integrity. The conclusion of this study is that H. vitripennis cells are capable of being cultured and used for mass production of HoCV-01 at a suitable level to allow production of a biopesticide.

Characterization of Dak Nong virus, an insect nidovirus isolated from Culex mosquitoes in Vietnam.

In this study, we isolated and characterized an insect nidovirus from the mosquito Culex tritaeniorhynchus Giles (Diptera: Culicidae) in Vietnam, as an additional member of the new family Mesoniviridae in the order Nidovirales. The virus, designated "Dak Nong virus (DKNV)," shared many characteristics with Cavally virus and Nam Dinh virus, which have also been discovered recently in mosquitoes, and these viruses should be considered members of a single virus species, Alphamesonivirus 1. DKNV grew in cultured mosquito cells but could not replicate in the cultured vertebrate cells tested. N-terminal sequencing of the DKNV structural proteins revealed two posttranslational cleavage sites in the spike glycoprotein precursor. DKNV is assumed to be a new member of the species Alphamesonivirus 1, and the current study provides further understanding of viruses belonging to the new family Mesoniviridae.

Global honey bee viral landscape altered by a parasitic mite.

Emerging diseases are among the greatest threats to honey bees. Unfortunately, where and when an emerging disease will appear are almost impossible to predict. The arrival of the parasitic Varroa mite into the Hawaiian honey bee population allowed us to investigate changes in the prevalence, load, and strain diversity of honey bee viruses. The mite increased the prevalence of a single viral species, deformed wing virus (DWV), from ~10 to 100% within honey bee populations, which was accompanied by a millionfold increase in viral titer and a massive reduction in DWV diversity, leading to the predominance of a single DWV strain. Therefore, the global spread of Varroa has selected DWV variants that have emerged to allow it to become one of the most widely distributed and contagious insect viruses on the planet.

A new insect cell line from pupal ovary of Spodoptera exigua established by stimulation with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG).

A continuous cell line derived from the pupal ovary of Spodoptera exigua was established by treating primary cells with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). Three days after treating cells with 3.0 µg/ml of MNNG, the cells formed a monolayer and were initially subcultured 60 d after the MNNG was removed, followed by subculturing for 30 passages. The established cell line, designated IOZCAS-Spex 12, consisted of a mixture of three types of cells, including spherical, spindle-shaped, and oval cells. The population doubling time of the cell line during its logarithmic growth phase was found to be 71 h. DNA amplification fingerprinting polymerase chain reaction analysis confirmed that the new cell line originated from S. exigua. Susceptibility of IOZCAS-Spex 12 cells to infection by certain nucleopolyhedroviruses was investigated. The results showed that the cell line was highly susceptible to infection by S. exigua nucleopolyhedrovirus and Autographa californica multiple nucleopolyhedrovirus, slightly susceptible to infection by Spodoptera litura nucleopolyhedrovirus, and not susceptible to infection by Helicoverpa armigera nucleopolyhedroviruses or Hyphantria cunea nucleopolyhedroviruses. The results of this study suggest that MNNG treatment may overcome existing limitations to obtaining continually proliferating cells and may open up the possibilities for immortalizing isolated insect cells.

Worker honeybee sterility: a proteomic analysis of suppressed ovary activation.

Eusocial behavior is extensively studied in the honeybee, Apis mellifera, as it displays an extreme form of altruism. Honeybee workers are generally obligatory sterile in a bee colony headed by a queen, but the inhibition of ovary activation is lifted upon the absence of queen and larvae. Worker bees are then able to develop mature, viable eggs. The detailed repressive physiological mechanisms that are responsible for this remarkable phenomenon are as of yet largely unknown. Physiological studies today mainly focus on the transcriptome, while the proteome stays rather unexplored. Here, we present a quantitative 2-dimensional differential gel electrophoresis comparison between activated and inactivated worker ovaries and brains of reproductive and sterile worker bees, including a spot map of ovaries, containing 197 identified spots. Our findings suggest that suppression of ovary activation might involve a constant interplay between primordial oogenesis and subsequent degradation, which is probably mediated through steroid and neuropeptide hormone signaling. Additionally, the observation of higher viral protein loads in both the brains and ovaries of sterile workers is particularly noteworthy. This data set will be of great value for future research unraveling the physiological mechanisms underlying the altruistic sterility in honeybee workers.

Disease dynamics and persistence of Musca domestica salivary gland hypertrophy virus infections in laboratory house fly (Musca domestica) populations.

Past surveys of feral house fly populations have shown that Musca domestica salivary gland hypertrophy virus (MdSGHV) has a worldwide distribution, with an average prevalence varying between 0.5% and 10%. How this adult-specific virus persists in nature is unknown. In the present study, experiments were conducted to examine short-term transmission efficiency and long-term persistence of symptomatic MdSGHV infections in confined house fly populations. Average rates of disease transmission from virus-infected to healthy flies in small populations of 50 or 100 flies ranged from 3% to 24% and did not vary between three tested geographical strains that originated from different continents. Introduction of an initial proportion of 40% infected flies into fly populations did not result in epizootics. Instead, long-term observations demonstrated that MdSGHV infection levels declined over time, resulting in a 10% infection rate after passing through 10 filial generations. In all experiments, induced disease rates were significantly higher in male flies than in female flies and might be explained by male-specific behaviors that increased contact with viremic flies and/or virus-contaminated surfaces.

Host phylogeny determines viral persistence and replication in novel hosts.

Pathogens switching to new hosts can result in the emergence of new infectious diseases, and determining which species are likely to be sources of such host shifts is essential to understanding disease threats to both humans and wildlife. However, the factors that determine whether a pathogen can infect a novel host are poorly understood. We have examined the ability of three host-specific RNA-viruses (Drosophila sigma viruses from the family Rhabdoviridae) to persist and replicate in 51 different species of Drosophilidae. Using a novel analytical approach we found that the host phylogeny could explain most of the variation in viral replication and persistence between different host species. This effect is partly driven by viruses reaching a higher titre in those novel hosts most closely related to the original host. However, there is also a strong effect of host phylogeny that is independent of the distance from the original host, with viral titres being similar in groups of related hosts. Most of this effect could be explained by variation in general susceptibility to all three sigma viruses, as there is a strong phylogenetic correlation in the titres of the three viruses. These results suggest that the source of new emerging diseases may often be predictable from the host phylogeny, but that the effect may be more complex than simply causing most host shifts to occur between closely related hosts.

Infectious genomic RNA of Rhopalosiphum padi virus transcribed in vitro from a full-length cDNA clone.

Availability of a cloned genome from which infectious RNA can be transcribed is essential for investigating RNA virus molecular mechanisms. To date, no such clones have been reported for the Dicistroviridae, an emerging family of invertebrate viruses. Previously we demonstrated baculovirus-driven expression of a cloned Rhopalosiphum padi virus (RhPV; Dicistroviridae) genome that was infectious to aphids, and we identified a cell line (GWSS-Z10) from the glassy-winged sharpshooter, that supports RhPV replication. Here we report that RNA transcribed from a full-length cDNA clone is infectious. Transfection of GWSS-Z10 cells with the RhPV transcript resulted in cytopathic effects, ultrastructural changes, and accumulation of progeny virions, consistent with virus infection. Virions from transcript-infected cells were infectious in aphids. This infectious transcript of a cloned RhPV genome provides a valuable tool, and a more tractable system without interference from baculovirus infection, for investigating replication and pathogenesis of dicistroviruses.

Spread of infectious chronic bee paralysis virus by honeybee (Apis mellifera L.) feces.

Knowledge of the spreading mechanism of honeybee pathogens within the hive is crucial to our understanding of bee disease dynamics. The aim of this study was to assess the presence of infectious chronic bee paralysis virus (CBPV) in bee excreta and evaluate its possible role as an indirect route of infection. Samples of paralyzed bees were (i) produced by experimental inoculation with purified virus and (ii) collected from hives exhibiting chronic paralysis. CBPV in bee heads or feces (crude or absorbed onto paper) was detected by reverse transcription-PCR. CBPV infectivity was assessed by intrathoracic inoculation of bees with virus extracted from feces and by placement of naive bees in cages previously occupied by contaminated individuals. CBPV RNA was systematically detected in the feces of naturally and experimentally infected bees and on the paper sheets that had been used to cover the floors of units containing bees artificially infected with CBPV or the floor of one naturally infected colony. Both intrathoracic inoculation of bees with virus extracted from feces and placement of bees in contaminated cages provoked overt disease in naive bees, thereby proving that the excreted virus was infectious and that this indirect route of infection could lead to overt chronic paralysis. This is the first experimental confirmation that infectious CBPV particles excreted in the feces of infected bees can infect naive bees and provoke overt disease by mere confinement of naive bees in a soiled environment.

In vitro host range of the Hz-1 nonoccluded virus in insect cell lines.

A total of 13 insect cell lines spanning 4 orders (Lepidoptera, Coleoptera, Diptera, and Homoptera) were tested for their ability to replicate the nonoccluded virus Hz-1. Only the Lepidopteran cell lines supported replication of the virus with TN-CL1 and BCIRL-HZ-AM1 producing the highest titers of 2.4 x 10(8) tissue culture infective dose (TCID)50/ml and 2.0 x 10(8) TCID50/ml, respectively. A codling moth cell line (CP-169) was the only Lepidopteran cell line that did not replicate the virus and transfection of this cell line with Hz-1 DNA failed to replicate the virus. Also, transfection with DNA from a recombinant baculovirus carrying the red fluorescent protein gene (AcMNPVhsp70 Red) was not expressed in CP-169 cells. The replication cycle of Hz-1 in BCIRL-HZ-AM1 cells showed that this virus replicated rapidly starting at 16 h postinoculation (p.i.) and reaching a peak titer of 1.0 x 10(8) TCID50/ml 56 h postinoculation. Hz-1 when compared with several other baculoviruses has the widest in vitro host spectrum.

A glassy-winged sharpshooter cell line supports replication of Rhopalosiphum padi virus (Dicistroviridae).

Rhopalosiphum padi virus (RhPV) (family Dicistroviridae; genus Cripavirus) is an icosahedral aphid virus with a 10kb positive-sense RNA genome. To study the molecular biology of RhPV, identification of a cell line that supports replication of the virus is essential. We screened nine cell lines derived from species within the Lepidoptera, Diptera and Hemiptera for susceptibility to RhPV following RNA transfection. We observed cytopathic effects (CPE) only in cell lines derived from hemipterans, specifically GWSS-Z10 cells derived from the glassy winged sharp shooter, Homalodisca coagulata and DMII-AM cells derived from the corn leaf hopper, Dalbulus maidis. Translation and appropriate processing of viral gene products, RNA replication and packaging of virus particles in the cytoplasm of GWSS-Z10 cells were examined by Western blot analysis, Northern blot hybridization and electron microscopy. Infectivity of the GWSS-Z10 cell derived-virus particles to the bird cherry-oat aphid, R. padi, was confirmed by RT-PCR and Western blot. The GWSS-Z10 cell line provides a valuable tool to investigate replication, structure and assembly of RhPV.

Small compounds targeted to subunit interfaces arrest maturation in a nonenveloped, icosahedral animal virus.

Nudaurelia omega capensis virus (N omega V) capsids were previously characterized in two morphological forms, a T=4, 485-A-diameter round particle with large pores and a tightly sealed 395-A icosahedrally shaped particle with the same quasi-symmetric surface lattice. The large particle converts to the smaller particle when the pH is lowered from 7.6 to 5, and this activates an autocatalytic cleavage of the viral subunit at residue 570. Here we report that both 1-anilino-8 naphthalene sulfonate (ANS) and the covalent attachment of the thiol-reactive fluorophore, maleimide-ANS (MIANS), inhibit the structural transition and proteolysis at the lower pH. When ANS is exhaustively washed from the particles, the maturation proceeds normally; however, MIANS-modified particles are still inhibited after the same washing treatment, indicating that covalent attachment targets MIANS to a critical location for inhibition. Characterization of the low-pH MIANS product by electron cryo-microscopy (cryo-EM) and image reconstruction demonstrated a morphology intermediate between the two forms previously characterized. A pseudoatomic model of the intermediate configuration was generated by rigid body refinement of the X-ray structure of the subunits (previously determined in the assembled capsid) into the cryo-EM density, allowing a quantitative description of the inhibited intermediate and a hypothesis for the mechanism of the inhibition.

Genetic and phenotypic characterization of the newly described insect flavivirus, Kamiti River virus.

We have described in the accompanying paper by Sang, et al., ([57], Arch Virol 2003, in press) the isolation and identification of a new flavivirus, Kamiti River virus (KRV), from Ae. macintoshi mosquitoes that were collected as larvae and pupae from flooded dambos in Central Province, Kenya. Among known flaviviruses, KRV was shown to be most similar to, but genetically and phenotypically distinct from, Cell fusing agent virus (CFAV). KRV was provisionally identified as an insect-only flavivirus that fails to replicate in vertebrate cells or in mice. We report here the further characterization of KRV. Growth in cell culture was compared to that of CFAV; although growth kinetics were similar, KRV did not cause the cell fusion that is characteristic of CFAV infection. The KRV genome was found to be 11,375 nucleotides in length, containing a single open reading frame encoding 10 viral proteins. Likely polyprotein cleavage sites were identified, which were most similar to those of CFAV and were comparable to those of other flaviviruses. Sequence identity with other flaviviruses was low; maximum identity was with CFAV. Possible terminal secondary structures for the 5' and 3' non-coding regions (NCR) were similar to those predicted for other flaviviruses. Whereas CFAV was isolated from insect cells in the laboratory, the isolation of KRV demonstrates the presence of an insect-only flavivirus in nature and raises questions regarding potential interactions between this virus and other mosquito-borne viruses in competent vector populations. Additionally, this virus will be an important tool in future studies to determine markers associated with flavivirus host specificity.

Sensitivity of Invertebrate iridescent virus 6 to organic solvents, detergents, enzymes and temperature treatment.

The sensitivity of Invertebrate iridescent virus 6 (IIV-6) to a selection of organic solvents, detergents, enzymes and heat treatment was assayed in Spodoptera frugiperda (Sf9) cells and by injection of inoculum into larvae of Galleria mellonella. In several cases, the degree of sensitivity of the virus depended on the method of assay; cell culture assays indicated greater losses of activity than insect bioassay. IIV-6 was sensitive to chloroform but sensitivity to ether was only detected by cell culture assay. Sensitivity (defined as a reduction of at least 1 log activity) was detected following treatment by 1 and 0.1% SDS, 1% Triton-X100, 70% ethanol, 70% methanol, 1% sodium deoxycholate, pH 11.1 and 3.0. No sensitivity was detected to 1% Tween 80, 1 M MgCl2, 100 mM EDTA, lipase, phospholipase A2, proteinase K, or trypsin at the concentrations tested. Viral activity was reduced by approximately 4 logs following heating to 70 degrees C for 60 min or 80 degrees C for 30 min. The above observations highlight the need for studies on the role of the virus lipid component in the process of particle entry into cells, and may explain why vertebrate and invertebrate iridoviruses have been reported to differ in their sensitivity to organic solvents and enzymes.

A refined method for the detection of baculovirus occlusion bodies in forest terrestrial and aquatic habitats.

A sensitive and efficient method was developed for the detection of genetically modified and wild-type baculovirus occlusion bodies (OB) in forest terrestrial and aquatic habitats. The protocol facilitates the analysis of a large number of samples collected and frozen to maintain viral integrity. Lyophilization was used to standardize the size of both field-collected soil samples and test substrates inoculated with OBs for the determination of minimum detection threshold. To simulate natural conditions, terrestrial test substrates were inoculated at a standardized moisture content determined using a soil pressure plate apparatus. OBs, extracted from lyophilized test substrates by washing, sieving and centrifugation, were subjected to alkaline lysis and viral DNA isolated using a purchased DNA purification kit. PCR amplified DNA was visualized using agarose gel electrophoresis. Minimum detection thresholds in terrestrial substrates were 10(3), 10(2), 10(2) and 10(1) OBs from 0.5 g of lyophilized L, F-H and mineral soil horizons, and 1.0 ml of leachate, respectively. Detection thresholds in aquatic substrates were 10(0) and 10(3) OBs from 1.0 ml of pond water and 1.0 g of bottom sediment, respectively.