The invasive Asian bush mosquito Aedes japonicus found in the Netherlands can experimentally transmit Zika virus and Usutu virus

Background - The Asian bush mosquito Aedes japonicus is invading Europe and was first discovered in Lelystad, the Netherlands in 2013, where it has established a permanent population. In this study, we investigated the vector competence of Ae. japonicus from the Netherlands for the emerging Zika virus (ZIKV) and zoonotic Usutu virus (USUV). ZIKV causes severe congenital microcephaly and Guillain-Barré syndrome in humans. USUV is closely related to West Nile virus, has recently spread throughout Europe and is causing mass mortality of birds. USUV infection in humans can result in clinical manifestations ranging from mild disease to severe neurological impairments.Methodology/Principal findings - In our study, field-collected Ae. japonicus females received an infectious blood meal with ZIKV or USUV by droplet feeding. After 14 days at 28°C, 3% of the ZIKV-blood fed mosquitoes and 13% of the USUV-blood fed mosquitoes showed virus-positive saliva, indicating that Ae. japonicus can transmit both viruses. To investigate the effect of the mosquito midgut barrier on virus transmission, female mosquitoes were intrathoracically injected with ZIKV or USUV. Of the injected mosquitoes, 96% (ZIKV) and 88% (USUV) showed virus-positive saliva after 14 days at 28°C. This indicates that ZIKV and USUV can efficiently replicate in Ae. japonicus but that a strong midgut barrier is normally restricting virus dissemination. Small RNA deep sequencing of orally infected mosquitoes confirmed active replication of ZIKV and USUV, as demonstrated by potent small interfering RNA responses against both viruses. Additionally, de novo small RNA assembly revealed the presence of a novel narnavirus in Ae. japonicus.Conclusions/Significance - Given that Ae. japonicus can experimentally transmit arthropod-borne viruses (arboviruses) like ZIKV and USUV and is currently expanding its territories, we should consider this mosquito as a potential vector for arboviral diseases in Europ

Comparative Usutu and West Nile virus transmission potential by local Culex pipiens mosquitoes in north-western Europe

Originating from Africa, Usutu virus (USUV) first emerged in Europe in 2001. This mosquito-borne flavivirus caused high mortality rates in its bird reservoirs, which strongly resembled the introduction of West Nile virus (WNV) in 1999 in the United States. Mosquitoes infected with USUV incidentally transmit the virus to other vertebrates, including humans, which can result in neuroinvasive disease. USUV and WNV co-circulate in parts of southern Europe, but the distribution of USUV extends into central and northwestern Europe. In the field, both viruses have been detected in the northern house mosquito Culex pipiens, of which the potential for USUV transmission is unknown. To understand the transmission dynamics and assess the potential spread of USUV, we determined the vector competence of C. pipiens for USUV and compared it with the well characterized WNV. We show for the first time that northwestern European mosquitoes are highly effective vectors for USUV, with infection rates of 11% at 18. °C and 53% at 23. °C, which are comparable with values obtained for WNV. Interestingly, at a high temperature of 28. °C, mosquitoes became more effectively infected with USUV (90%) than with WNV (58%), which could be attributed to barriers in the mosquito midgut. Small RNA deep sequencing of infected mosquitoes showed for both viruses a strong bias for 21-nucleotide small interfering (si)RNAs, which map across the entire viral genome both on the sense and antisense strand. No evidence for viral PIWI-associated RNA (piRNA) was found, suggesting that the siRNA pathway is the major small RNA pathway that targets USUV and WNV infection in C. pipiens mosquitoes

Alphavirus infection : Host cell shut-off and inhibition of antiviral responses

Alphaviruses cause debilitating disease in humans and animals and are transmitted by blood-feeding arthropods, typically mosquitoes. With a traditional focus on two models, Sindbis virus and Semliki Forest virus, alphavirus research has significantly intensified in the last decade partly due to the re-emergence and dramatic expansion of chikungunya virus in Asia, Europe, and the Americas. As a consequence, alphavirus–host interactions are now understood in much more molecular detail, and important novel mechanisms have been elucidated. It has become clear that alphaviruses not only cause a general host shut-off in infected vertebrate cells, but also specifically suppress different host antiviral pathways using their viral nonstructural proteins, nsP2 and nsP3. Here we review the current state of the art of alphavirus host cell shut-off of viral transcription and translation, and describe recent insights in viral subversion of interferon induction and signaling, the unfolded protein response, and stress granule assembly

Functional RNA during Zika virus infection

Zika virus (ZIKV; family Flaviviridae; genus Flavivirus) is a pathogenic mosquito-borne RNA virus that currently threatens human health in the Americas, large parts of Asia and occasionally elsewhere in the world. ZIKV infection is often asymptomatic but can cause severe symptoms including congenital microcephaly and Guillain-Barré syndrome. The positive single-stranded RNA genome of the mosquito-borne ZIKV requires effective replication in two evolutionary distinct hosts - mosquitoes and primates. In addition to some of the viral proteins, the ZIKV genomic RNA and functional RNAs produced thereof aid in the establishment of productive infection and the evasion of host cell antiviral responses. ZIKV has evolved to contain a nucleotide composition and RNA modifications, such as methylation and the formation of G-quadruplexes that allow effective replication in both hosts. Furthermore, a number of host factors interact with the viral genome to modulate RNA replication. Importantly, the ZIKV genome produces non-coding subgenomic flavivirus RNA (sfRNA) due to stalling of host 5'- 3' ribonucleases on viral RNA structures in the 3' untranslated region (UTR). This sfRNA (sfRNA) exerts important proviral functions such as antagonizing the innate interferon response and RNA interference. Here, we discuss the ZIKV genomic RNA and functional RNAs thereof to assess their significance during ZIKV infection. Understanding the details of the ZIKV infection cycle will aid in the development of effective antiviral strategies and safe vaccines

Vector competence of northern European Culex pipiens biotypes and hybrids for West Nile virus is differentially affected by temperature

Background: Outbreaks of West Nile virus (WNV) have not occurred in northern Europe despite nearby circulation of WNV in the southern part of the continent. The main vector for WNV, the mosquito Culex (Cx.) pipiens, consists of two behaviorally distinct biotypes, pipiens and molestus, which can form hybrids. Although temperature has been shown to influence vector competence of Cx. pipiens for WNV and biotypes are differentially susceptible towards infection, the interaction between the two has not been elucidated. Methods: We determined vector competence of the Cx. pipiens biotypes and hybrids, after 14 days of incubation at 18, 23 and 28 °C. Mosquitoes were orally infected by providing an infectious blood meal or by injecting WNV directly in the thorax. Infection and transmission rates were determined by testing the bodies and saliva for WNV presence. In addition, titers of mosquitoes with WNV-positive bodies and saliva samples were determined. Results: Orally infected biotype pipiens and hybrids showed significantly increased transmission rates with higher temperatures, up to 32 and 14 %, respectively. In contrast, the molestus biotype had an overall transmission rate of 10 %, which did not increase with temperature. All mosquitoes that were infected via WNV injections had (close to) 100 % infection and transmission rates, suggesting an important role of the mosquito midgut barrier. We found no effect of increasing temperature on viral titers. Conclusions: Temperature differentially affected vector competence of the Cx. pipiens biotypes. This shows the importance of accounting for biotype-by-temperature interactions, which influence the outcomes of vector competence studies. Vector competence studies with Cx. pipiens mosquitoes differentiated to the biotype level are essential for proper WNV risk assessments.</p

CpG and UpA dinucleotides in both coding and non-coding regions of echovirus 7 inhibit replication initiation post-entry

Most vertebrate and plant RNA and small DNA viruses suppress genomic CpG and UpA dinucleotide frequencies, apparently mimicking host mRNA composition. Artificially increasing CpG/UpA dinucleotides attenuates viruses through an entirely unknown mechanism. Using the echovirus 7 (E7) model in several cell types, we show that the restriction in E7 replication in mutants with increased CpG/UpA dinucleotides occurred immediately after viral entry, with incoming virions failing to form replication complexes. Sequences of CpG/UpA-high virus stocks showed no evidence of increased mutational errors that would render them replication defective, these viral RNAs were not differentially sequestered in cytoplasmic stress granules nor did they induce a systemic antiviral state. Importantly, restriction was not mediated through effects on translation efficiency since replicons with high CpG/UpA sequences inserted into a non-coding region were similarly replication defective. Host-cells thus possess intrinsic defence pathways that prevent replication of viruses with increased CpG/UpA frequencies independently of codon usage

Vara god eller göra gott? : en studie av 2008års hållbarhetsredovisningar i statligt ägda företag

Chikungunya virus (CHIKV) is a mosquito-borne alphavirus that has evolved effective mechanisms to counteract the type I interferon (IFN) response. Upon recognition of the virus, cells secrete IFNs, which signal through transmembrane receptors (IFNAR) to phosphorylate STAT proteins (pSTAT). pSTAT dimers are transported into the nucleus by importin-α5 and activate the transcription of IFNstimulated genes (ISGs), increasing cellular resistance to infection. Subsequently, STAT proteins are shuttled back into the cytoplasm by the exportin CRM1. CHIKV nonstructural protein 2 (nsP2) reduces ISG expression by inhibiting general host cell transcription and by specifically reducing the levels of nuclear pSTAT1 via an unknown mechanism. To systematically examine where nsP2 acts within the JAK/STAT signaling cascade, we used two well-characterized mutants of nsP2, P718S and KR649AA. Both mutations abrogate nsP2's ability to shut off host transcription, but only the KR649AA mutant localizes exclusively to the cytoplasm and no longer specifically inhibits JAK/STAT signaling. These mutant nsP2 proteins did not differentially affect IFNAR expression levels or STAT1 phosphorylation in response to IFNs. Coimmunoprecipitation experiments showed that in the presence of nsP2, STAT1 still effectively bound importin-α5. Chemically blocking CRM1-mediated nuclear export in the presence of nsP2 additionally showed that nuclear translocation of STAT1 is not affected by nsP2. nsP2 putatively has five domains. Redirecting the nsP2 KR649AA mutant or just nsP2's C-terminal methyltransferase-like domain into the nucleus strongly reduced nuclear pSTAT in response to IFN stimulation. This demonstrates that the C-terminal domain of nuclear nsP2 specifically inhibits the IFN response by promoting the nuclear export of STAT1.</p

Virus interferes with host-seeking behaviour of mosquito

Transmission of vector-borne pathogens is dependent on the hostseeking behaviour of their vector. Pathogen manipulation of the hostseeking behaviour of vectors towards susceptible hosts is supposedly beneficial for transmission. For West Nile virus (WNV), manipulation of the host-seeking behaviour of the main mosquito vector towards birds would be advantageous, because mammals are dead-end hosts. We hypothesised that WNV infection induces a stronger host-seeking response and a shift in host preference towards birds, to enhance its transmission by mosquitoes. However, here we show that WNV infection decreases the host-seeking response, and does not induce a shift in mosquito host preference. Other fitnessrelated traits are not affected by WNV infection. No effect of WNV infectionwas found on antennal electrophysiological responsiveness. Thus, the reduced host-seeking response is likely to result from interference in the mosquito's central nervous system. This is the first study that shows changes, specifically in the host-seeking behaviour induced by a pathogen, that do not favour transmission.</p