Flaviviruses constitute the most relevant group of arthropod-transmitted viruses, including important human pathogens such as the dengue, Zika, yellow fever, and West Nile viruses. The natural alternation of these viruses between vertebrate and invertebrate hosts shapes the viral genome population, which leads to selection of different viral variants with potential implications for epidemiological fitness and pathogenesis. However, the selective forces and mechanisms acting on the viral RNA during host adaptation are still largely unknown. Here, we found that two almost identical tandem RNA structures present at the viral 3′ untranslated region are under different selective pressures in the two hosts. Mechanistic studies indicated that the two RNA elements, known as dumbbells, contain sequences that overlap essential RNA cyclization elements involved in viral RNA synthesis. The data support a model in which the duplicated RNA structures differentially evolved to accommodate distinct functions for viral replication in the two hosts.

The dengue virus genome is a dynamic molecule that adopts different conformations in the infected cell. Here, using RNA folding predictions, chemical probing analysis, RNA binding assays, and functional studies, we identified new cis-acting elements present in the capsid coding sequence that facilitate cyclization of the viral RNA by hybridization with a sequence involved in a local dumbbell structure at the viral 3= untranslated region (UTR). The identified interaction differentially enhances viral replication in mosquito and mammalian cells. Dengue virus (DENV) is a member of the Flaviviridae family that includes other important pathogens such as yellow fever virus (YFV), West Nile virus (WNV), Saint Louis encephalitis virus (SLEV), and Japanese encephalitis virus (JEV). The DENV genome is a plus-stranded RNA molecule that contains a single open reading frame flanked by highly structured 5= and 3= untranslated regions (UTRs) (1-3). RNA elements located within these regions are responsible for translation initiation and genome replication (4-7). The 5= UTR is about 100 nucleotides (nt) long and includes three different elements: (i) stem-loop A (SLA), which is the promoter for viral polymerase binding and activation (8-10); (ii) stem-loop B (SLB), which contains a sequence known as 5= upstream of the AUG region (5= UAR) that is complementary to a sequence present at the 3= UTR (3= UAR) and mediates longrange RNA-RNA interactions between the ends of the genome (11); and (iii) a spacer sequence between SLA and SLB rich in U's, which functions as an enhancer of viral replication (10). The viral 3= UTR is about 450 nucleotides long and comprises four defined domains: domain A1, which features a variable region (VR) (12); domains A2 and A3, which present two almost-identical dumbbell-like secondary structures (DB1 and DB2), which appear to work as enhancers for viral RNA replication (13-15); and domain A4, which contains a small hairpin (sHP) and the 3= stem-loop (3= SL), which are essential elements for viral replication (3,16). In addition to RNA structures defined in the UTRs that play different roles during infection, important RNA elements have been described in the protein coding region. In this regard, essential sequences that mediate long-range RNA-RNA interactions known as 5= cyclization sequence (5= CS) and 5= downstream of AUG region (5= DAR) are located within the capsid coding sequence (11,13,(17)(18)(19)(20)(21). Also, a hairpin known as cHP, located between 5= CS and 5= DAR, has been shown to be necessary for efficient RNA replication (22). The current model for viral RNA synthesis includes the interaction of the viral polymerase NS5 with the 5=-end SLA promoter and its transfer to the 3=-end initiation site by cyclization of the viral genome (9). Despite great advances in knowledge of cis-acting RNA elements in the flavivirus genomes, the molecular details and mechanisms by which many of them function during viral replication are still not well understood.Intrigued by dual roles of RNA sequences in v...

To help understand the mechanism of pathogenesis of dengue virus (DV), we set out to create an infectious cDNA of the Brazilian prototype strain of DV serotype 1 (DV1-BR/90). PCR-amplified fragments of DV1-BR/90 cDNA were readily assembled into a subgenomic cDNA that could be used to produce replicating RNAs (replicons), lacking the structural protein-encoding regions of the genome. However, assembly of a cDNA capable of producing infectious virus was only possible using a bacterial artificial chromosome plasmid, indicating that DV1 sequences were especially difficult to propagate in E. coli. While characterizing our cDNA we discovered a fortuitous temperature-sensitive mutation in the NS1 encoding region. Using our infectious cDNA and a renilla luciferase-expressing replicon we were able to demonstrate that this mutation produced a defect in RNA replication at 37 degrees C, demonstrating that the DV1 NS1 protein plays an essential role in RNA replication.

Dengue virus is a mosquito-borne flavivirus that has a large impact in global health. It is considered as one of the medically important arboviruses, and developing a preventive or therapeutic solution remains a top priority in the medical and scientific community. Drug discovery programs for potential dengue antivirals have increased dramatically over the last decade, largely in part to the introduction of high-throughput assays. In this study, we have developed an image-based dengue high-throughput/high-content assay (HT/HCA) using an innovative computer vision approach to screen a kinase-focused library for anti-dengue compounds. Using this dengue HT/HCA, we identified a group of compounds with a 4-(1-aminoethyl)-N-methylthiazol-2-amine as a common core structure that inhibits dengue viral infection in a human liver-derived cell line (Huh-7.5 cells). Compounds CND1201, CND1203 and CND1243 exhibited strong antiviral activities against all four dengue serotypes. Plaque reduction and time-of-addition assays suggests that these compounds interfere with the late stage of viral infection cycle. These findings demonstrate that our image-based dengue HT/HCA is a reliable tool that can be used to screen various chemical libraries for potential dengue antiviral candidates.

Zika virus (ZIKV) is an emerging flavivirus mainly transmitted by mosquitoes that represents a global health threat. A common feature of flavivirus infected cells is the accumulation of viral non-coding subgenomic RNAs by partial degradation of the viral genome, known as sfRNAs, involved in immune evasion and pathogenesis. Although a great effort is being placed to understand the mechanism by which these sfRNAs function during infection, the picture of how they work is still incomplete. In this study, we developed new genetic tools to dissect the functions of ZIKV RNA structures for viral replication and sfRNA production in mosquito and human hosts. ZIKV infections mostly accumulate two kinds of sfRNAs, sfRNA1 and sfRNA2, by stalling genome degradation upstream of duplicated stem loops (SLI and SLII) of the viral 3′UTR. Although the two SLs share conserved sequences and structures, different functions have been found for ZIKV replication in human and mosquito cells. While both SLs are enhancers for viral infection in human cells, they play opposite roles in the mosquito host. The dissection of determinants for sfRNA formation indicated a strong cooperativity between SLI and SLII, supporting a high order organization of this region of the 3′UTR. Using recombinant ZIKV with different SLI and SLII arrangements, which produce different types of sfRNAs or lack the ability to generate these molecules, revealed that at least one sfRNA was necessary for efficient infection and transmission in Aedes aegypti mosquitoes. Importantly, we demonstrate an absolute requirement of sfRNAs for ZIKV propagation in human cells. In this regard, viruses lacking sfRNAs, constructed by deletion of the region containing SLI and SLII, were able to infect human cells but the infection was rapidly cleared by antiviral responses. Our findings are unique for ZIKV since previous studies with other flaviviruses with deletions of analogous regions of the genome, including dengue and West Nile viruses, accumulated distinct species of sfRNAs and were infectious in human cells. We conclude that flaviviruses share common strategies for sfRNA generation, but they have evolved mechanisms to produce different kinds of these RNAs to accomplish virus-specific functions. IMPORTANCE Flaviviruses are important emerging and reemerging human pathogens. Understanding the molecular mechanisms for viral replication and evasion of host antiviral responses are relevant to develop control strategies. Flavivirus infections produce viral non-coding RNAs, known as sfRNAs, involved in viral replication and pathogenesis. Here, we dissected molecular determinants for Zika virus sfRNA generation in the two natural hosts, human cells and mosquitoes. We found that two RNA structures of the viral 3′UTR operate in a cooperative manner to produce two species of sfRNAs, and that the deletion of these elements have a profoundly different impact on viral replication in the two hosts. Generation of at least one sfRNA was necessary for efficient Zika virus infection of Aedes aegypti mosquitoes. Moreover, recombinant viruses with different 3′UTR arrangements revealed an essential role of sfRNAs for productive infection in human cells. In summary, we define molecular requirements for Zika virus sfRNA accumulation and provide new ideas of how flavivirus RNA structures have evolved to succeed in different hosts.

Hantavirus pulmonary syndrome (HPS) is an emerging disease caused by an increasing number of distinct hantavirus serotypes found worldwide. It is also a very severe immune disease. It progresses quickly and is associated with a high mortality rate. At the prodrome phase, hantavirosis symptoms can resemble those of other infectious diseases such as leptospirosis and influenza. Thus, prognosis could be improved by developing a rapid and sensitive diagnostic test for hantavirus infection, and by improving knowledge about clinical aspects of this disease. This study describes clinical features and laboratory parameters throughout the course of HPS in 98 patients. We report the seasonality and regional distribution of this disease in Paraná State, Brazil during the last seven years. In addition, we evaluated a specific molecular diagnostic test based on a nested reverse transcriptase-polymerase chain reaction for the detection of hantaviruses circulating in Brazil.

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Abstract. Paraná state presents the fourth highest number of accumulated cases of hantavirus pulmonary syndrome in Brazil. To map the risk areas for hantavirus transmission we carried out a study based on rodent trapping and determined the anti-hantavirus seroprevalence in these animals and in the inhabitants of these localities. Overall seroprevalence in rodents and humans were 2.5% and 2.4%, respectively. Eighty-two percent of the seropositive rodents were genetically analyzed. Phylogenetic analyses revealed that hantaviruses from rodent samples cluster with Araucá ria (Juquitiba-like) or Jaborá hantavirus genotypes. The Jaborá strain was identified in Akodon serrensis and Akodon montensis, whereas the Araucá ria strain was detected in Oligoryzomys nigripes, Oxymycterus judex, A. montensis, and Akodon paranaensis, with the latter species being identified for the first time as a natural host. These findings expose the complex relationships between virus and reservoirs in Brazil, which could have an impact on hantavirus transmission dynamics in nature and human epidemiology.