Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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Vector competence of northern and southern European Culex pipiens pipiens mosquitoes for West Nile virus across a gradient of temperatures
Vogels, C.B.F. ; Göertz, G.P. ; Pijlman, G.P. ; Koenraadt, C.J.M. - \ 2017
Medical and Veterinary Entomology 31 (2017)4. - ISSN 0269-283X - p. 358 - 364.
Arbovirus - Culex pipiens complex - Infection - Italy - Northern house mosquito - The Netherlands - Transmission

In Europe, West Nile virus (WNV) outbreaks have been limited to southern and central European countries. However, competent mosquito vectors and susceptible bird hosts are present in northern Europe. Differences in temperature and vector competence of mosquito populations may explain the absence of WNV outbreaks in northern Europe. The aim of the present study was to directly compare vector competence of northern and southern European Culex pipiens (Cx. p.) pipiens mosquitoes for WNV across a gradient of temperatures. WNV infection and transmission rates were determined for two Cx. p. pipiens populations originating from The Netherlands and Italy, respectively. Mosquitoes were orally exposed by providing an infectious bloodmeal, or by injecting WNV (lineage 2) in the thorax, followed by 14-day incubation at 18, 23, or 28°C. No differences in infection or transmission rates were found between the Cx. p. pipiens populations with both infection methods, but WNV transmission rates were significantly higher at temperatures above 18°C. The absence of WNV outbreaks in northern Europe cannot be explained by differences in vector competence between Cx. p. pipiens populations originating from northern and southern Europe. This study suggests that low temperature is a key limiting factor for WNV transmission.

Vector competence of northern European Culex pipiens biotypes and hybrids for West Nile virus is differentially affected by temperature
Vogels, Chantal B.F. ; Fros, Jelke J. ; Goertz, Giel ; Pijlman, Gorben P. ; Koenraadt, Sander - \ 2016
Parasites & Vectors 9 (2016)1. - ISSN 1756-3305
Arbovirus - Culex - Infection - Temperature - Vector competence - West Nile virus

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.

Serological Evidence for Schmallenberg Virus Infection in Sheep of Portugal 2014
Esteves, Fernando ; Mesquita, João R. ; Vala, Helena ; Abreu-Silva, Joana ; Poel, W.H.M. Van Der; Nascimento, Maria S.J. - \ 2016
Vector-Borne and Zoonotic Diseases 16 (2016)1. - ISSN 1530-3667 - p. 63 - 65.
Arbovirus - ELISA. - Schmallenberg virus - Seroprevalence - Sheep

Between November and December of 2014, a serosurvey was set up to evaluate the presence of Schmallenberg virus (SBV) antibodies in sheep of Portugal. Sera (n = 1068) were tested using an indirect enzyme linked immunosorbent assay (ID Screen® Schmallenberg virus indirect, IDvet Innovative Diagnostics Montpellier, France). The estimated occurrence of immunogobulin G (IgG) antibodies against SBV in sheep of Portugal was 12.8% (95% confidence interval 11.0-15.0%). This is the first study reporting the presence of SBV antibodies in sheep of Portugal.

Non-structural protein NS3/NS3a is required for propagation of bluetongue virus in Culicoides sonorensis
Feenstra, Femke ; Drolet, B.S. ; Boonstra, Jan ; Rijn, P.A. Van - \ 2015
Parasites & Vectors 8 (2015)1. - ISSN 1756-3305 - 9 p.
Arbovirus - Bluetongue virus - Culicoides - DISA vaccine - Midge - NS3/NS3a

Background: Bluetongue virus (BTV) causes non-contagious haemorrhagic disease in ruminants and is transmitted by Culicoides spp. biting midges. BTV encodes four non-structural proteins of which NS3/NS3a is functional in virus release. NS3/NS3a is not essential for in vitro virus replication. However, deletion of NS3/NS3a leads to delayed virus release from mammalian cells and largely reduces virus release from insect cells. NS3/NS3a knockout BTV in sheep causes no viremia, but induces sterile immunity and is therefore proposed to be a Disabled Infectious Single Animal (DISA) vaccine candidate. In the absence of viremia, uptake of this vaccine strain by blood-feeding midges would be highly unlikely. Nevertheless, unintended replication of vaccine strains within vectors, and subsequent recombination or re-assortment resulting in virulent phenotypes and transmission is a safety concern of modified-live vaccines. Methods: The role of NS3/NS3a in replication and dissemination of BTV1, expressing VP2 of serotype 2 within colonized Culicoides sonorensis midges was investigated. Virus strains were generated using reverse genetics and their growth was examined in vitro. A laboratory colony of C. sonorensis, a known competent BTV vector, was fed or injected with BTV with or without expressing NS3/NS3a and replication in the midge was examined using RT PCR. Crossing of the midgut infection barrier was examined by separate testing of midge heads and bodies. Results: Although the parental NS3/NS3a expressing strain was not able to replicate and disseminate within C. sonorensis after oral feeding, this virus was able to replicate efficiently when the midgut infection barrier was bypassed by intrathoracic injection, whereas the NS3/NS3a knockout mutant was unable to replicate. This demonstrates that NS3/NS3a is required for viral replication within Culicoides. Conclusion: The lack of viremia and the inability to replicate within the vector, clearly demonstrate the inability of NS3/NS3a knockout DISA vaccine strains to be transmitted by midges.

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