The potential for reassortment between Oropouche and Schmallenberg Orthobunyaviruses

A number of viruses within the Peribunyaviridae family are naturally occurring reassortants, a common phenomenon for segmented viruses. Using a minigenome-reporter and virus-like particle (VLP) production assay, we have accessed the potential of Oropouche virus (OROV), Schmallenberg virus (SBV), and other orthobunyaviruses within the Simbu serogroup to reassort. We found that the untranslated region (UTR) in the medium segment is a potential contributing factor for reassortment by the tested viruses. We demonstrate that for promoter activity to occur it was essential that the viral RNA polymerase (L) and nucleocapsid (N) proteins were from the same virus, reinforcing the hypothesis that the large and small segments that encode these proteins segregate together during genome reassortment. Our results indicate that, given the right epidemiological setting, reassortment between SBV and OROV would potentially be feasible and could contribute to the emergence of a new Simbu virus

Genetic analysis of members of the species Oropouche virus and identification of a novel M segment sequence

Oropouche virus (OROV) is a public health threat in South America, and in particular Northern Brazil, causing frequent outbreaks of febrile illness. Using a combination of deep sequencing and Sanger sequencing approaches we have determined complete genome sequences of eight clinical isolates that were obtained from patient sera during an Oropouche fever outbreak in Amapa state, northern Brazil in 2009. We also report complete genome sequences of two OROV reassortants isolated from two marmosets in Minas Gerais state, southeast Brazil in 2012 that contain a novel M genome segment. Interestingly, all ten isolates posses a 947 nucleotide long S segment that lacks 11 residues in the S segment 3' UTR compared to the recently redetermined Brazilian prototype OROV strain BeAn19991. OROV maybe circulating more widely in Brazil and in the non-human primate population than previously appreciated and the identification of yet another reassortant highlights the importance of bunyavirus surveillance in South America

Establishment of a minigenome system for oropouche virus reveals the S genome segment to be significantly longer than reported previously

Oropouche virus (OROV) is a medically important orthobunyavirus, which causes frequent outbreaks of a febrile illness in the northern parts of Brazil. However, despite being the cause of an estimated half a million human infections since its first isolation in Trinidad in 1955, details of the molecular biology of this tripartite, negative-sense RNA virus remain limited. We have determined the complete nucleotide sequence of the Brazilian prototype strain of OROV, BeAn 19991, and found a number of differences compared with sequences in the database. Most notable were that the S segment contained an additional 204 nt at the 3′ end and that there was a critical nucleotide mismatch at position 9 within the base-paired terminal panhandle structure of each genome segment. In addition, we obtained the complete sequence of the Trinidadian prototype strain TRVL-9760 that showed similar characteristics to the BeAn 19991 strain. By using a T7 RNA polymerase-driven minigenome system, we demonstrated that cDNA clones of the BeAn 19991 L and S segments expressed functional proteins, and also that the newly determined terminal untranslated sequences acted as functional promoters in the minigenome assay. By co-transfecting a cDNA to the viral glycoproteins, virus-like particles were generated that packaged a minigenome and were capable of infecting naive cells

Interferon-stimulated gene (ISG)-expression screening reveals the specific antibunyaviral activity of ISG20

Bunyaviruses pose a significant threat to human health, prosperity and food security. In response to viral infections, interferons (IFNs) upregulate the expression of hundreds of interferon stimulated genes (ISGs) whose cumulative action can potently inhibit the replication of bunyaviruses. We used a flow cytometry-based method to screen the ability of ∼500 unique ISGs from humans and rhesus macaques to inhibit the replication of Bunyamwera orthobunyavirus (BUNV), the prototype of both the Peribunyaviridae family and Bunyavirales order. Candidates possessing antibunyaviral activity were further examined using a panel of divergent bunyaviruses. Interestingly, one candidate, ISG20, exhibited potent antibunyaviral activity against most viruses examined from the Peribunyaviridae, Hantaviridae and Nairoviridae families, whereas phleboviruses (Phenuiviridae) largely escaped inhibition. Similar to other viruses known to be targeted by ISG20, the antibunyaviral activity of ISG20 is dependent upon its functional ribonuclease activity. Through use of an infectious VLP assay (based on the BUNV minigenome system), we confirmed that gene expression from all 3 viral segments is strongly inhibited by ISG20. Using in vitro evolution, we generated a substantially ISG20-resistant BUNV and mapped the determinants of ISG20 sensitivity/resistance. Taken together, we report that ISG20 is a broad and potent antibunyaviral factor yet some bunyaviruses are remarkably ISG20 resistant. Thus, ISG20 sensitivity/resistance could influence the pathogenesis of bunyaviruses, many of which are emerging viruses of clinical or veterinary significance

Sustained replication of synthetic canine distemper virus defective genomes in vitro and in vivo

Defective interfering (DI) genomes have long been considered inconvenient artifacts that suppressed viral replication in vitr

Sensitivity to BST-2 restriction correlates with Orthobunyavirus host range

Orthobunyaviruses include several recently emerging viruses of significant medical and veterinary importance. There is currently very limited understanding on what determines the host species range of these pathogens. In this study we discovered that BST-2/tetherin restricts orthobunyavirus replication in a host-specific manner. We show that viruses with human tropism (Oropouche virus and La Crosse virus) are restricted by sheep BST-2 but not by the human orthologue, while viruses with ruminant tropism (Schmallenberg virus and others) are restricted by human BST-2 but not by the sheep orthologue. We also show that BST-2 blocks orthobunyaviruses replication by reducing the amount of envelope glycoprotein into viral particles egressing from infected cells. This is the first study identifying a restriction factor that correlates with species susceptibility to orthobunyavirus infection. This work provides insight to help us dissect the adaptive changes that bunyaviruses require to cross the species barrier and emerge into new species

Generation of recombinant Oropouche viruses lacking the nonstructural protein NSm or NSs

Wellcome Trust provided funding to Richard M. Elliott under grant number 99220. Medical Research Council (MRC) provided funding to Natasha Louise Tilston-Lunel under grant number 1101085. FAPESP-São Paulo Research Foundation provided funding to Gustavo Olszanski Acrani under grant number 2013/02798-0.Oropouche virus (OROV) is a midge-borne human pathogen with a geographic distribution in South America. OROV was first isolated in 1955, and since then, it has been known to cause recurring outbreaks of a dengue-like illness in the Amazonian regions of Brazil. OROV, however, remains one of the most poorly understood emerging viral zoonoses. Here we describe the successful recovery of infectious OROV entirely from cDNA copies of its genome and generation of OROV mutant viruses lacking either the NSm or the NSs coding region. Characterization of the recombinant viruses carried out in vitro demonstrated that the NSs protein of OROV is an interferon (IFN) antagonist as in other NSs-encoding bunyaviruses. Additionally, we demonstrate the importance of the nine C-terminal amino acids of OROV NSs in IFN antagonistic activity. OROV was also found to be sensitive to IFN-α when cells were pretreated; however, the virus was still capable of replicating at doses as high as 10,000 U/ml of IFN-α, in contrast to the family prototype BUNV. We found that OROV lacking the NSm protein displayed characteristics similar to those of the wild-type virus, suggesting that the NSm protein is dispensable for virus replication in the mammalian and mosquito cell lines that were tested. IMPORTANCE Oropouche virus (OROV) is a public health threat in Central and South America, where it causes periodic outbreaks of dengue-like illness. In Brazil, OROV is the second most frequent cause of arboviral febrile illness after dengue virus, and with the current rates of urban expansion, more cases of this emerging viral zoonosis could occur. To better understand the molecular biology of OROV, we have successfully rescued the virus along with mutants. We have established that the C terminus of the NSs protein is important in interferon antagonism and that the NSm protein is dispensable for virus replication in cell culture. The tools described in this paper are important in terms of understanding this important yet neglected human pathogen.PostprintPeer reviewe

Establishment of a minigenome system for Oropouche virus reveals the S genome segment to be significantly longer than reported previously

Oropouche virus (OROV) is a medically important orthobunyavirus, which causes frequent outbreaks of a febrile illness in the northern parts of Brazil. However, despite being the cause of an estimated half a million human infections since its first isolation in Trinidad in 1955, details of the molecular biology of this tripartite, negative-sense RNA virus remain limited. We have determined the complete nucleotide sequence of the Brazilian prototype strain of OROV, BeAn 19991, and found a number of differences compared with sequences in the database. Most notable were that the S segment contained an additional 204 nt at the 3′ end and that there was a critical nucleotide mismatch at position 9 within the base-paired terminal panhandle structure of each genome segment. In addition, we obtained the complete sequence of the Trinidadian prototype strain TRVL-9760 that showed similar characteristics to the BeAn 19991 strain. By using a T7 RNA polymerase-driven minigenome system, we demonstrated that cDNA clones of the BeAn 19991 L and S segments expressed functional proteins, and also that the newly determined terminal untranslated sequences acted as functional promoters in the minigenome assay. By co-transfecting a cDNA to the viral glycoproteins, virus-like particles were generated that packaged a minigenome and were capable of infecting naive cells