Host signaling pathways play important roles in the replication of influenza virus, but their functional effects remain to be characterized at the molecular level. Here we identify two receptor tyrosine kinase inhibitors (RTKIs) of the tyrphostin class that exhibit robust antiviral activity against influenza A virus replication in cultured cells. One of these (AG879) is a selective inhibitor of the nerve growth factor receptor and human epidermal growth factor receptor 2 (TrkA/HER2) signaling; the other, tyrphostin A9 (A9), inhibits the plateletderived growth factor receptor (PDGFR) pathway. We find that each inhibits at least three postentry steps of the influenza virus life cycle: AG879 and A9 both strongly inhibit the synthesis of all three influenza virus RNA species, block Crm1-dependent nuclear export, and also prevent the release of viral particles through a pathway that is modulated by the lipid biosynthesis enzyme farnesyl diphosphate synthase (FPPS). Tests of short hairpin RNA (shRNA) knockdown and additional small-molecule inhibitors confirmed that interventions targeting TrkA can suppress influenza virus replication. Our study suggests that host cell receptor tyrosine kinase signaling is required for maximal influenza virus RNA synthesis, viral ribonucleoprotein (vRNP) nuclear export, and virus release and that specific RTKIs hold promise as novel anti-influenza virus therapeutics.

Viruses are obligate intracellular parasites; they heavily depend on the host cell machinery to effectively replicate and produce new progeny virus particles. Following viral infection, diverse cell signaling pathways are initiated by the cells, with the major goal of establishing an antiviral state. However, viruses have been shown to exploit cellular signaling pathways for their own effective replication. Genome-wide siRNA screens have also identified numerous host factors that either support (proviral) or inhibit (antiviral) virus replication. Some of the host factors might be dispensable for the host but may be critical for virus replication; therefore such cellular factors may serve as targets for development of antiviral therapeutics. Mitogen activated protein kinase (MAPK) is a major cell signaling pathway that is known to be activated by diverse group of viruses. MAPK interacting kinase 1 (MNK1) has been shown to regulate both cap-dependent and internal ribosomal entry sites (IRES)-mediated mRNA translation. In this review we have discuss the role of MAPK in virus replication, particularly the role of MNK1 in replication and translation of viral genome.

Several arenaviruses can cause hemorrhagic fever diseases (VHFs) in humans, the pathogenic mechanism of which is poorly understood due to their virulent nature and the lack of molecular clones. A safe, convenient, and economical small animal model of arenavirus hemorrhagic fever is based on guinea pigs infected by the arenavirus Pichinde (PICV). PICV does not cause disease in humans, but an adapted strain of PICV (P18) causes a disease in guinea pigs that mimics arenavirus hemorrhagic fever in humans in many aspects, while a low-passaged strain (P2) remains avirulent in infected animals. In order to identify the virulence determinants within the PICV genome, we developed the molecular clones for both the avirulent P2 and virulent P18 viruses. Recombinant viruses were generated by transfecting plasmids that contain the antigenomic L and S RNA segments of PICV under the control of the T7 promoter into BSRT7-5 cells, which constitutively express T7 RNA polymerase. By analyzing viral growth kinetics in vitro and virulence in vivo, we show that the recombinant viruses accurately recapitulate the replication and virulence natures of their respective parental viruses. Both parental and recombinant virulent viruses led to high levels of viremia and titers in different organs of the infected animals, whereas the avirulent viruses were effectively controlled and cleared by the hosts. These novel infectious clones for the PICV provide essential tools to identify the virulence factors that are responsible for the severe VHF-like disease in infected animals.Arenaviruses are enveloped RNA viruses with single-stranded ambisense RNA genomes (6). The genomes of these viruses consist of two RNA segments, the large (L) segment of ϳ7.2 kb and the small (S) segment of ϳ3.4 kb (6). The L RNA segment encodes the viral polymerase L protein in a negative orientation and a small multifunctional Z protein in a positive sense. The S RNA segment encodes the nucleoprotein NP in a negative orientation and the envelope glycoprotein precursor GPC in a positive sense (6). The terminal 19 nucleotides (nt) from both ends of the segments are imperfectly complementary to each other and are predicted to form the panhandle structures that serve as the cis-acting elements required for viral RNA transcription and replication (15,23,24,33). A unique feature of the arenavirus genomic RNAs is the noncoding intergenic regions located between the two open reading frames (6). They range from 59 to 217 nt in length and are predicted to form one to three energetically stable stem-loop structures (6, 40) that are proposed to contribute to transcriptional termination. Currently, the only available molecular clone of arenavirus was developed for the prototype lymphocytic choriomeningitis virus (LCMV) (13,38). This system has served as an invaluable tool to study the biological functions of arenavirus proteins and RNA elements.

SUMMARY Antiviral drugs have traditionally been developed by directly targeting essential viral components. However, this strategy often fails due to the rapid generation of drug-resistant viruses. Recent genome-wide approaches, such as those employing small interfering RNA (siRNA) or clustered regularly interspaced short palindromic repeats (CRISPR) or those using small molecule chemical inhibitors targeting the cellular “kinome,” have been used successfully to identify cellular factors that can support virus replication. Since some of these cellular factors are critical for virus replication, but are dispensable for the host, they can serve as novel targets for antiviral drug development. In addition, potentiation of immune responses, regulation of cytokine storms, and modulation of epigenetic changes upon virus infections are also feasible approaches to control infections. Because it is less likely that viruses will mutate to replace missing cellular functions, the chance of generating drug-resistant mutants with host-targeted inhibitor approaches is minimized. However, drug resistance against some host-directed agents can, in fact, occur under certain circumstances, such as long-term selection pressure of a host-directed antiviral agent that can allow the virus the opportunity to adapt to use an alternate host factor or to alter its affinity toward the target that confers resistance. This review describes novel approaches for antiviral drug development with a focus on host-directed therapies and the potential mechanisms that may account for the acquisition of antiviral drug resistance against host-directed agents.

Duck virus enteritis (DVE), also called duck plague, is one of the major contagious and fatal diseases of ducks, geese and swan. It is caused by duck enteritis virus (DEV)/Anatid herpesvirus-1 of the genus Mardivirus, family Herpesviridae, and subfamily Alpha-herpesvirinae. Of note, DVE has worldwide distribution, wherein migratory waterfowl plays a crucial role in its transmission within and between continents. Furthermore, horizontal and/ or vertical transmission plays a significant role in disease spread through oral-fecal discharges. Either of sexes from varying age groups of ducks is vulnerable to DVE. The disease is characterized by sudden death, vascular damage and subsequent internal hemorrhage, lesions in lymphoid organs, digestive mucosal eruptions, severe diarrhea and degenerative lesions in parenchymatous organs. Huge economic losses are connected with acute nature of the disease, increased morbidity and mortality (5%-100%), condemnations of carcasses, decreased egg production and hatchability. Although clinical manifestations and histopathology can provide preliminary diagnosis, the confirmatory diagnosis involves virus isolation and detection using serological and molecular tests. For prophylaxis, both live-attenuated and killed vaccines are being used in broiler and breeder ducks above 2 weeks of age. Since DEV is capable of becoming latent as well as shed intermittently, recombinant subunit and DNA vaccines either alone or in combination (polyvalent) are being targeted for its benign prevention. This review describes DEV, epidemiology, transmission, the disease (DVE), pathogenesis, and advances in diagnosis, vaccination and antiviral agents/therapies along with appropriate prevention and control strategies.