Master of Science / Department of Diagnostic Medicine/Pathobiology / Ying Fang / Seneca Valley Virus (SVV) causes vesicular disease in pigs. Vesicular lesions on the snout and coronary band of hoof mostly resemble lesions caused by Foot-and-Mouth Disease Virus (FMDV), which may lead to the foreign animal disease investigation. In 2015, Brazil experienced major outbreaks of SVV; then in July, sporadic cases of SVV were reported in United States and became a concern in swine industry. A reverse-genetic system serves as a major tool to study pathogenesis of the virus. In our study, a full-length cDNA infectious clone, pKS15-01-Clone, was constructed from an emerging Seneca Valley Virus (SVV; strain KS15-01). To explore the potential use as a viral backbone for expressing marker genes, the enhanced green fluorescent protein (EGFP)-tagged reporter virus (vKS15-01-EGFP) was generated using reverse genetics. Compared to the parental virus, the pKS15-01-Clone derived virus (vKS15-01-Clone) replicated efficiently in vitro and in vivo, and induced similar levels of neutralizing antibody and cytokine responses in infected animals. In contrast, the vKS15-01-EGFP virus showed impaired growth ability and induced lower level of immune response in infected animals. Lesions on the dorsal snout and coronary bands were observed in all pigs infected by parental virus KS15-01, but not in pigs infected with vKS15-01-Clone or vKS15-01-EGFP viruses. These results demonstrated that the infectious clone and EGFP reporter virus will be important tools in further elucidating the SVV pathogenesis and development of control measures.

No description available.

Mosquito-borne viruses, such as dengue virus (DENV), Zika virus (ZIKV), chikungunya virus (CHIKV), yellow fever virus (YFV), Japanese encephalitis virus (JEV), and West Nile virus (WNV) are major threats to global public health resulting in millions of infections and hundreds of thousands of deaths annually. The presence of these viruses and their increasing emergence/spread continues to escalate. Notably, Usutu virus (USUV; Genus: Flavivirus; Family: Flaviviridae) is one such pathogen currently causing mass die-offs of avian hosts throughout Europe. USUV is categorized in the Japanese Encephalitis virus (JEV) antigenic complex and thus shares many antigenic and pathologic characteristics with fellow members, such as JEV and WNV. Respective to human infections, USUV cases are generally asymptomatic; nonetheless, acute cases have been reported. These acute cases typically cause mild symptoms, such as fevers and rashes; however, more severe cases can result in neurologic diseases, such as encephalitis and/or meningoencephalitis. In addition to these pathologic similarities, USUV shares several ecological and geographical traits with WNV, a pathogen responsible for several outbreaks during its spread from Africa, to Europe, and eventually the United States. Currently, WNV is considered endemic in areas across the United States due to its transmission via Culex spp.; mosquitoes that are ubiquitous in the United States. These parallels suggest the possible emergence of USUV into the United States and therefore, it is imperative to broaden our knowledge of USUV and assess its potential to become a major global health concern. The overall goal of this thesis was to characterize USUV and evaluate its emergence potential in the United States by: (1) developing infectious clones of recent European and African USUV isolates as tools for characterization and analysis of USUV and (2) assessing the transmission potential of several species of North American mosquitoes. In Aim 1, we show that the aforementioned infectious clones infect and replicate similarly to their parental strains in vitro in both vertebrate and invertebrate models, as well as in transiently immunocompromised CD-1 and IFNAR-/- murine models, and thus serve as useful tools for future molecular studies focusing on USUV. Furthermore, in Aim 2, we describe the ability of field-caught (Southwest Virginia, USA) Culex spp. and Aedes spp. mosquitoes to become infected with a recent European isolate of USUV; although, we report an overall limited potential for these species to transmit this virus. Altogether, these studies form a foundation for understanding the potential emergence of USUV in the United States as well as provide necessary tools needed to aid future research on USUV emergence, transmission, and pathogenesis. / Master of Science / Usutu virus (USUV) is an emerging mosquito-borne virus that was first isolated from a mosquito in 1959 in South Africa, and since then, has become a major problem throughout Africa and Europe causing acute to severe infection in dozens of patients. Additionally, this virus is causing massive die-offs in Eurasian blackbird populations. This is particularly problematic because birds play a critical role in ecosystems as they act as forms of pest control, pollinators, and seed dispersers. Depletion of these species could lead to an imbalance and, eventually, collapse of our natural ecosystem. Additionally, there is a growing concern of USUV making its way into the United States, following a similar track of emergence to WNV's introduction in New York in 1999 and its subsequent spread throughout the states. WNV's introduction to the United States was detrimental to native bird populations and humans, and has caused tens of thousands of infections and thousands of deaths since this introduction. Research has shown USUV causes similar disease symptoms to WNV. The self-limiting illness from these viruses typically includes fever and rashes but some infections can result in more severe cases causing inflammation of the brain and surrounding areas. Like many other prominent mosquito-borne viruses, there is no specific treatment or vaccine for WNV or USUV. Because USUV is so closely related to WNV, and their similar characteristics may point towards similar emergence in the United States, it is essential to garner more information on USUV. The overall goal of this thesis was to establish a reliable tool(s) for further characterization of USUV and demonstrate the potential for USUV emergence in the United States. We first developed molecular tools, known as viral clones, that are valuable to the scientific community which allows the manipulation of USUV genetic material to perform further downstream studies. Our objective for this initial study was to create a molecular tool that would behave similarly to their natural, or "parental", virus. The results from this study suggest we have successfully produced these tools. Furthermore, we sought to determine the potential for field-caught mosquitoes from Southwest Virginia, USA to transmit a recently isolated strain of USUV. These data suggest that while these mosquitoes do have the ability to become infected with USUV, they have a limited potential to transmit this virus to animal hosts. Altogether, these studies have allowed us to expand our knowledge on USUV's potential emergence in the United States and develop powerful tools to continue this essential research.

Thesis (PhD)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Grapevine fanleaf virus (GFLV) is one of the oldest, most widespread and devastating viruses infecting grapevine, and occurs globally where Vitis vinifera is grown. In South Africa (SA) GFLV is predominant in the Breede River Valley, one of the highest wine producing regions in SA. To date, only three GFLV isolates have been completely sequenced internationally, and limited sequence information is available for SA GFLV isolates. In this study, the first full-length GFLV genome sequence from a South African isolate, GFLV-SAPCS3, was determined. Full-length sequences were used for phylogenetic analysis and revealed that the SA isolates are separate from other sequenced GFLV isolates. Full-length sequences were also used to investigate putative intra- and interspecies recombination events involving GFLV-SAPCS3 RNA1 and RNA2 between GFLV and Arabis mosaic virus (ArMV) isolates. Using two different recombination analysis software packages, the most notable of the putative recombination events involving GFLV-SAPCS3 indicated that the GFLV-SAPCS3 RNA2 5’ UTR might have evolved from an interspecies recombination event between GFLVF13- type and ArMV Ta-type isolates. The presence of satellite RNAs (satRNA) associated with South African GFLV isolates was also investigated. In a collaborative study (see Chapter 4 for details), more than a 100 GFLV- infected grapevine plants were screened for satRNAs. SatRNAs were present in only two plants, containing isolates GFLV-SACH44 and GFLV-SACH47. The full-length nucleotide sequences of the GFLV-SACH44 genomic RNAs 1 and 2, and the associated satRNA were determined. No significant sequence variation could be detected between the GFLV isolates that had the presence of a satRNA and those that had not. The GFLV-SACH44 RNA2 5’ UTR also had the same conserved sequence that was found in GFLVSAPCS3, which suggests that GFLV-SACH44, like GFLV-SAPCS3, may have arisen from a common ancestor, which may have originated from an interspecies recombination event. The GFLV-SACH44 satRNA was found to be more closely related to the ArMV large satRNA than to the satRNA associated with GFLV-F13. A full-length cDNA clone of GFLV-SACH44 satRNA was constructed and its replication and systemic spread in herbaceous hosts, when mechanically co-inoculated with two GFLV isolates as helper viruses, was demonstrated. Replication of the GFLV-SACH44 satRNA cDNA clone was however abolished when co-inoculated with an ArMV helper virus, even though it is phylogenetically more closely related to ArMV satRNAs. The full-length satRNA clones were modified to be used as vectors for expression and/or silencing of foreign genes, by inserting the green fluorescence protein (GFP) full-length or partial sequences downstream of the open reading frame of the satRNA. These constructs were cloned into a binary vector to allow for agro-infiltration into plants. Full-length cDNA clones of GFLV-SAPCS3 RNA1 and RNA2 were constructed to be used in conjunction with modified GFLV-SACH44 satRNA full-length clones. The full length GFLV-SAPCS3 RNA1 and RNA2 clones were however not infectious in Nicotiana benthamiana after agro-infiltration and therefore the evaluation of the modified satRNA expression and silencing constructs had to be aborted. Attempts to understand this failure revealed that, among other point mutations, four frameshifts had occurred in the RNA1 full-length clone, rendering the transcripts untranslatable, and hence noninfectious. Strategies to correct the mutations are discussed. Once these mutations have been corrected this study can continue in evaluating the use of the satRNA component for expression and silencing analysis. / AFRIKAANSE OPSOMMING: Grapevine fanleaf virus (GFLV) is een van die oudste, mees wydverspreide en mees verwoestende virusse wat wingerd affekteer en word wêreldwyd waar Vitis vinifera verbou word, gevind. In Suid Afrika (SA) kom GFLV veral in die Breederivier vallei, een van die mees produktiewe wyn-produserende areas in SA, voor. Tot dusver is daar net drie GFLV isolate waarvan die volledige nukleïensuurvolgorde internasionaal bepaal is. Die nukleïensuurvolgorde informasie vir SA GFLV isolate is redelik beperk. In hierdie studie was die eerste volledige nukleïensuurvolgorde van ‘n SA GFLV isolaat, GFLVSAPCS3, bepaal. Die volledige nukleïensuurvolgordes was vir filogenetiese analise gebruik, en vermeende intra- en interspesie rekombinasie gebeurtenisse, wat GFLVSAPCS3 RNA1 en RNA2 betrek, tussen GFLV en Arabis mosaic virus (ArMV) isolate was ondersoek. Twee verskillende rekombinasie-analise sagteware programme was gebruik en die noemenswaardigste van die vermeende rekombinasie gebeurtenisse, met betrekking tot GFLV-SAPCS3, het aangedui dat die GFLV-SAPCS3 RNA2 5’ ontransleerde streek (UTR) waarskynlik van ‘n interspesie rekombinasie gebeurtenis tussen ‘n GFLV-F13-tipe en ‘n ArMV-Ta-tipe isolaat ontwikkel het. Die teenwoordigheid van satelliet RNAs (satRNAs), wat met SA GFLV isolate geassosieer is, was ook ondersoek. Meer as ‘n 100 GFLV ge-infekteerde wingerd plante was in ‘n samewerkingsprojek (sien Hoofstuk 4 vir besonderhede) getoets vir die teenwoordigheid van satRNAs. SatRNAs was net in twee plante teenwoordig, in isolate GFLV-SACH44 en GFLV-SACH47. Die vollengte nukleïensuurvolgordes van GFLVSACH44 RNA1, RNA2 en geassosieerde satRNA was bepaal. Geen beduidende volgorde variasie tussen die GFLV isolate wat satRNAs bevat het, en die GFLV isolate sonder satRNA was waargeneem nie. Die GFLV-SACH44 RNA2 5’ UTR het ook die gekonserveerde volgorde, wat in GFLV-SAPCS3 teenwoordig was, gehad en dit dui daarop dat GFLV-SACH44, soos GFLV-SAPCS3, van dieselfde stamvader, wat tydens ‘n vorige rekombinasie gebeurtenis ontstaan het, mag ontwikkel het. Die GFLVSACH44 satRNA was meer naverwant aan die ArMV satRNAs as aan die satRNA, wat met GFLV-F13. ‘n Vollengte cDNA kloon van die GFLV-SACH44 satRNA was ontwikkel en die replisering en sistemiese verspreiding in sagte plante, nadat dit met twee GFLV isolate as helper virusse saam ge-inokuleer was, was gedemonstreer. Replisering van die GFLV-SACH44 satRNA cDNA kloon was egter ontwrig toe dit saam met ‘n ArMV helper virus saam ge-inokuleer was, al is dit filogeneties meer verwant aan ArMV satRNAs. Die vol-lengte satRNA klone was gemodifiseer om as vektore vir uitdrukking en/of uitdowing van transgene te dien, deur om vol-lengte of gedeeltelike groen fluoressensie proteïen (GFP) nukleïensuurvolgordes aan die einde van die satRNA leesraam te koppel. Hierdie konstrukte was in ‘n binêre vektor gekloon om agroinfiltrasie in plante toe te laat. Vol-lengte cDNA klone van GFLV-SAPCS3 RNA1 en RNA2 was ontwikkel om in samewerking met die gemodifiseerde GFLV-SACH44 satRNA konstrukte gebruik te word. Die vol-lengte GFLV-SAPCS3 RNA1 en RNA2 klone het egter nie in Nicotiana benthamiana gerepliseer na agro-infiltrasie nie, daarom was die evaluasie van die gemodifiseerde satRNA konstrukte gestaak. Pogings om die mislukking te verstaan, het daarop gewys dat, behalwe punt mutasies, vier leesraam versteurings in die RNA1 vollengte kloon voorgekom het, wat ontransleerbare transkripte, en dus nie-repliserende konstrukte tot gevolg gehad het. Strategieë om die mutasies te korrigeer is bespreek. Sodra die mutasies gekorrigeer is, kan die studie voortgaan om te evalueer of die satRNA komponent vir uitdrukking en uitdowing analise gebruik kan word.

Le virus West Nile (VWN) est un virus neurotrope principalement transmis par piqûre de moustique et dont le réservoir est constitué par la faune aviaire sauvage. Les souches circulant en Europe appartiennent à 4 lignages génétiques différents à l’origine de nombreuses épidémies d’ampleur modérée à faible et limitées géographiquement, contrairement à ce qui a été observé en Amérique du Nord. En 1998 en Israël, une importante épidémie a a été associée pour la première fois à une forte mortalité de la faune aviaire sauvage. Le virus (souche IS-98-ST1, lignage 1a) a été isolé du cerveau d’une cigogne moribonde. L’objet de cette thèse a été de construire un clone infectieux de la souche IS-98-ST1 afin d’en explorer les propriétés de neuroinvasion et de pouvoir mettre en évidence les déterminants moléculaires de sa virulence.Le virus obtenu à partir de la construction clone infectieux s’est révélé posséder les mêmes propriétés biologiques que le virus parental, que ce soit in vitro sur cellules Vero ou in vivo sur souris sensibles ou résistantes ou encore sur l’embryon de poulet. L’embryon de poulet est présenté ici comme un nouveau modèle d’évaluation de la virulence du VWN. Un modèle cellulaire neuronale (lignée de neuroblastomes humains, SK-N-SH) est aussi évalué dans ce manuscrit. En conclusion, un nouvel outil de génétique inverse a été obtenu pour le VWN. Cet outil permettra de travailler sur l’impact de mutations ponctuelles, ou de modifications plus importantes touchant un ou plusieurs gènes viraux sur la virulence du VWN, spécifiquement dans le contexte européen. / West Nile virus (WNV) is a neurotropic virus mainly transmitted through mosquito bites. Wild birds represent the main reservoir hosts. Strains circulating in Europe belong to four lineages and have caused numerous but limited epidemics over the last few years. In 1998, an important outbreak associated to huge bird fatalities caused by a highly neuroinvasive strain (IS-98-ST1) took place in Israel. We aimed at producing a new infectious clone, based on the lineage 1a IS-98-ST1 WNV strain, for the characterization of its neuroinvasion properties as well as the molecular determinants of European WNV virulence. The growth kinetics of recombinant and parental WNV were similar in Vero cells. Moreover, the phenotypes of recombinant and parental WNV were indistinguishable in terms of viremia, viral load in the brain and mortality in susceptible and resistant mice. Finally, the pathobiology of the infectious clone was examined in embryonated chicken eggs, proposed as a new model for the evaluation of WNV virulence. The potential of human neuroblastoma cells (SK-N-SH) to discriminate between highly and mildly virulent WNV strains was assayed. In conclusion: a new molecular tool that is useful for the study of molecular determinants of WNV virulence has been generated. We take advantage of the high genetic stability of our one-piece infectious WNV cDNA clone to produce mutant viruses through the insertion of point mutations or the exchange of genetic fragments between WNV strains into the backbone of the IS-98-ST1 infectious clone.

Los virus producen graves pérdidas económicas en la agricultura. Esta problemática es muy dinámica ya que cada año aparecen nuevas virosis y es frecuente los fenómenos de emergencia con una rápida expansión de los virus. El control de las enfermedades víricas resulta poco eficaz en muchos casos porque la población viral es capaz de evolucionar y superar dichas estrategias. Por ello es clave entender la dinámica de las poblaciones y los factores implicados en la evolución de los virus con respecto a distintos aspectos de su biología del ciclo viral: replicación, movimiento dentro de la planta, respuesta a los mecanismos de defensa de la planta, transmisión a otras plantas, etc. El objetivo de esta tesis ha sido el estudio de los factores implicados en la evolución de dos virus que difieren en su variabilidad genética y gama de huéspedes: i) el Virus 1 del marchitamiento del haba (Broad bean wilt virus 1, BBWV-1), del género Fabavirus; y ii) el Virus del mosaico del tabaco (Tobacco mosaic virus, TMV) del género Tobamovirus. Primero se han desarrollado una serie de herramientas metodológicas que han permitido la detección rápida de BBWV-1 mediante hibridación molecular de improntas, la detección y cuantificación de BBWV-1 y TMV y su diferenciación de otras virosis del mismo género mediante RT-PCR cuantitativa a tiempo real. Se ha llevado a cabo la construcción de clones de cDNA del genoma completo de BBWV-1 para obtener transcritos infecciosos que puedan ser usados para estudiar la biología molecular, evolución y epidemiología. Una vez desarrollado esta metodología se ha usado para evaluar la eficacia biológica de BBWV-1 en el huésped y el efecto de algunos factores: concentración del inóculo, estado de desarrollo de la planta, tipo de huésped, aplicación de un activador de la defensa de la planta, y la infección con otro virus. Así mismo se han estudiado los factores relacionados con la eficacia biológica del virus durante su transmisión por pulgones: título viral / Ferriol Safont, I. (2012). FACTORS INVOLVED IN THE EVOLUTION OF BROAD BEAN WILT VIRUS 1 AND TOBACCO MOSAIC VIRUS [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/16000 / Palancia

African monkey species are natural hosts of simian hemorrhagic fever virus (SHFV) and develop persistent, asymptomatic infections. SHFV was previously shown to also cause a rapid onset fatal hemorrhagic fever disease in macaques. Infection of macaques with a new isolate of SHFV from persistently infected baboon sera, that showed high nucleotide identity with the lab strain LVR, resulted in viremia, pro-inflammatory cytokine and tissue factor production, and symptoms of coagulation defects. Primary macrophages and myeloid dendritic cell cultures from disease-susceptible macaques efficiently replicated SHFV and produced pro-inflammatory cytokines, including IL-6 and TNF-α, as well as tissue factor. Cells from disease resistant baboons produced low virus yields and the immunomodulatory cytokine IL-10. IL-10 treatment of macaque cells decreased IL-6 levels but had no effect on TNF-α levels, tissue factor or virus production suggesting that IL-10 plays a role in modulating immunopathology in disease-resistant baboons but not in regulating the efficiency of virus replication. SHFV is a member of the family Arteriviridae. The SHFV genome encodes 8 minor structural proteins. Other arteriviruses encode 4 minor structural proteins. Amino acid sequence comparisons suggest that the four additional SHFV minor structural proteins resulted from gene duplication. A full-length infectious clone of SHFV was constructed and produced virus with replication kinetics comparable to the parental virus. Mutant infectious clones, each with the start codon of one of the minor structural proteins substituted, were analyzed. All eight SHFV proteins were required for infectious virus production. The SHFV nonstructural polyprotein is processed into the mature replicase proteins by several viral proteases including papain-like cysteine proteases (PLPs). Only one or two PLP domains are present in other arteriviruses but SHFV has three PLP domains. Analysis of in vitro proteolytic processing of C- and N-terminally tagged polyproteins indicated that the PLP in each of the three SHFV nsp1 proteins is active. However, the nsp1α protease is more similar to a cysteine protease than a PLP. Analysis of the subcellular localization of the three SHFV nsp1 proteins indicated they have divergent functions.

African monkey species are natural hosts of simian hemorrhagic fever virus (SHFV) and develop persistent, asymptomatic infections. SHFV was previously shown to also cause a rapid onset fatal hemorrhagic fever disease in macaques. Infection of macaques with a new isolate of SHFV from persistently infected baboon sera, that showed high nucleotide identity with the lab strain LVR, resulted in viremia, pro-inflammatory cytokine and tissue factor production, and symptoms of coagulation defects. Primary macrophages and myeloid dendritic cell cultures from disease-susceptible macaques efficiently replicated SHFV and produced pro-inflammatory cytokines, including IL-6 and TNF-α, as well as tissue factor. Cells from disease resistant baboons produced low virus yields and the immunomodulatory cytokine IL-10. IL-10 treatment of macaque cells decreased IL-6 levels but had no effect on TNF-α levels, tissue factor or virus production suggesting that IL-10 plays a role in modulating immunopathology in disease-resistant baboons but not in regulating the efficiency of virus replication. SHFV is a member of the family Arteriviridae. The SHFV genome encodes 8 minor structural proteins. Other arteriviruses encode 4 minor structural proteins. Amino acid sequence comparisons suggest that the four additional SHFV minor structural proteins resulted from gene duplication. A full-length infectious clone of SHFV was constructed and produced virus with replication kinetics comparable to the parental virus. Mutant infectious clones, each with the start codon of one of the minor structural proteins substituted, were analyzed. All eight SHFV proteins were required for infectious virus production. The SHFV nonstructural polyprotein is processed into the mature replicase proteins by several viral proteases including papain-like cysteine proteases (PLPs). Only one or two PLP domains are present in other arteriviruses but SHFV has three PLP domains. Analysis of in vitro proteolytic processing of C- and N-terminally tagged polyproteins indicated that the PLP in each of the three SHFV nsp1 proteins is active. However, the nsp1α protease is more similar to a cysteine protease than a PLP. Analysis of the subcellular localization of the three SHFV nsp1 proteins indicated they have divergent functions.

Currently, human norovirus is the leading cause of acute gastroenteritis and accounts for most cases of foodborne illnesses in the United States each year. Due to its tissue culture inefficiency, studies of human norovirus have been crippled for more than forty years.Tulane virus (TV) stands out as a suitable surrogate of human norovirus given its high amino acid identity with human norovirus and its well-established cell culture system. It was first isolated from rhesus macaques (Macaca mulatta) in 2008 and identified as a novel Calicivirusrepresenting a new genus, Recovirus genus (Farkas et al., 2008). However, there are still unanswered questions about its infectious cycle and the essential factors for its infection. In this study, we have obtained a TV variant (the 9-6-17 strain) that has lost the binding ability to the B-type histo-blood group antigen (HBGA), which was proposed to be the receptor of both TV and human norovirus. In the first chapter, we outline how the sequence analysis,structural biology studies, and mutagenesis studies of the 9-6-17 TV strain have shed light on the interaction with its host cell receptor. To investigate the key residues for HBGA binding, we established the full-length infectious clone of the 9-6-17 TV strain. We present a highly selective transformation of serine 367, located in the predicted HBGA binding site, into a lysine residu e. Our results advance the understanding of genetic changes in TV required for adaptation to cell culture environments. Cryo-EM is an awarding winning technique that has been the greatest scientific breakthrough in recent years. It was awarded the Nobel Prize in Chemistry in 2017. Despite the technological advances of the direct electron detector and image processing software, several major roadblocks remain for high-resolution structure determination with cryo-EM. In the later chapters, we explored the most efficient way of using VPP to enhance image contrast, how to tackle the airwater interface problem by encapsulating target protein, how to reach a higher resolution by refining high order parameters, and the helical indexing problem in real space. These technical advances would benefit the whole cryo-EM community by providing convenient tools or insights for future directions.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / Bovine viral diarrhea virus (BVDV) is a worldwide pathogen associated with important losses to livestock production. Most of these losses come from reproductive disorders and from the ability of the virus to produce persistent infections following in utero infection of the fetus. A number of reverse genetics methodologies have been used for BVDV in order to better understand the biology of the virus, which allowed the elucidation of a number of biological features including virus replication, host-virus interaction, immune response, and the pathogenesis of fetal infection. The present study describes the construction, characterization and manipulation of an infectious clone out of a non-cytophatic Brazilian BVDV strain IBSP4-ncp. The cDNA recombinant clone was constructed by yeast homologous recombination with a low-copy vector, from three genomic fragments comprising the open reading frame (ORF). The two untranslated regions (5' and 3' UTR) were replaced by the respective UTRs of the reference strain NADL. The constructed vector was transcribed in vitro and the resulting RNA was transfected on MDBK cells to rescue infectious virus. The rescued viruses (IC-pBSC_IBSP4-ncp#2 and #3) were maintained for ten passages in tissue culture and characterized in vitro, showing replication dynamics, focus size and morphology similar to those of the parental IBSP-4. Genomic analysis revealed five point mutations in the gene coding for Npro protein, resulting in amino acid changes. These mutations probably reflect an adaptation of the virus to the heterologous UTRs. The infectious clone IC-pBSC_IBSP4-ncp#2 was further used for the construction of a recombinant virus expressing the Gaussia luciferase (Gluc) reporter gene. The reporter gene was inserted between the Npro and Core genes, being flanked by an upstream linker and a downstream sequence of the Foot and Mouth Disease virus protease (FMDV2Apro) for accurate protein processing. The recombinant vector was in vitro transcribed and the RNA was transfected on MDBK cells. Recombinant infectious viruses were rescued (IC-pBSC_IBSP4-ncpGluc#3 and #4) and characterized in vitro, showing replication dynamics, focus size and morphology similar to those of the parental IBSP-4 clone. The Gluc reporter gene was accurately expressed and processed by the recombinant virus during 15 passages in tissue culture. These studies revealed that the infectious clone constructed herein can be easily manipulated and is able to carry in its genome heterologous genes up to 555 base pairs in length in a stable fashion and without interference with its replication efficiency. Thus, the constructed clone may be very useful for genetic manipulation towards studying different aspects of the BVDV biology and its interactions with the host, and for the development of vaccine strains with attenuated phenotype and/or with antigenic markers. / O vírus da diarreia viral bovina (BVDV) é um patógeno de bovinos distribuído mundialmente, associado com importantes perdas econômicas. As maiores perdas devem-se aos problemas reprodutivos causados pela infecção, e pela capacidade do vírus de causar persistência após infecção fetal no terço inicial da gestação. Para entender melhor a biologia desse vírus, sistemas de genética reversa foram desenvolvidos e tem permitido a elucidação de vários aspectos da replicação viral, interação vírus hospedeiro, resposta imune e patogenia da infecção fetal. O presente estudo relata a construção, caracterização e manipulação de um clone infeccioso, a partir da cepa brasileira não-citopática IBSP4-ncp. O clone de DNA recombinante foi construído pela técnica de recombinação homóloga em levedura, utilizando um vetor de baixo número de cópias, construído a partir de três fragmentos genômicos, que compreendiam a fase aberta de leitura (open reading frame, ORF) do vírus. As duas regiões não traduzidas (5 e 3 UTR) foram substituídas pelas respectivas UTRs da cepa de referência NADL. O vetor construído foi transcrito in vitro e o RNA obtido foi transfectado em células MDBK para recuperação de vírus infecciosos. Os vírus recuperados (CI-pBSC_IBSP4-ncp#2 e #3) foram mantidos por 10 passagens em cultivo celular e caracterizados in vitro, apresentando dinâmica de replicação, tamanho e morfologia de focos similares ao vírus parental IBSP-4. A análise do genoma por sequenciamento revelou cinco mutações pontuais no gene Npro, com trocas de aminoácidos, provavelmente refletindo uma adaptação do vírus às UTRs heterólogas. O clone infeccioso construído CIpBSC_ IBSP4-ncp#2, foi então utilizado para a construção de um vírus recombinante expressando o gene repórter Gaussia luciferase (Gluc). O gene repórter foi inserido entre os genes Npro e Core do vírus. Para o processamento da proteína repórter, uma sequência ligante foi adicionada anteriormente ao gene, e a sequência da protease do vírus da Febre Aftosa (FMDV2Apro) foi inserida após o gene. O vetor recombinante construído foi transcrito in vitro e o RNA obtido foi transfectado em células MDBK. Vírus recombinantes infecciosos foram recuperados (CI-pBSC_IBSP4-ncpGluc#3 e #4) e caracterizados in vitro, apresentando dinâmica de replicação, tamanho e morfologia de focos similares ao vírus obtido do clone infecioso. O gene repórter Gluc foi corretamente expresso e processado pelo vírus recombinante durante 15 passagens em cultivo celular. Com os resultados obtidos nestes estudos, conclui-se que o clone infeccioso construído pode ser facilmente manipulado e é capaz de carrear em seu genoma, e expressar de forma estável, genes heterólogos com até 555 pares de base, que parecem não interferir com sua capacidade replicativa. Dessa forma, o clone obtido pode ser muito útil para manipulação genética visando estudar diferentes aspectos da biologia do BVDV e de suas interações com o hospedeiro, assim como para a produção de cepas vacinais com fenótipo atenuado e/ou com marcadores antigênicos.