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.

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Development of a Virosomal RSV Vaccine Containing 3D-PHAD® Adjuvant : Formulation, Composition, and Long-Term Stability
Lederhofer, J. ; Lent, J. van; Bhoelan, F. ; Karneva, Z. ; Haan, A. de; Wilschut, J.C. ; Stegmann, T. - \ 2018
Pharmaceutical Research 35 (2018)9. - ISSN 0724-8741
adjuvant - monophosphoryl lipid A - respiratory syncytial virus - single particle tracking - vaccine - virosomes

Purpose: Characterization of virosomes, in late stage preclinical development as vaccines for Respiratory Syncytial Virus (RSV), with a membrane-incorporated synthetic monophosphoryl lipid A, 3D-PHAD® adjuvant. Methods: Virosomes were initially formed by contacting a lipid film containing 3D-PHAD® with viral membranes solubilized with the short chain phospholipid DCPC, followed by dialysis, later by adding solubilized 3D-PHAD to viral membranes, or to preformed virosomes from DMSO. Results: Virosomes formed from lipid films contained the membrane glycoproteins G and F, at similar F to G ratios but lower concentrations than in virus, and the added lipids, but only a fraction of the 3D-PHAD®. By single particle tracking (SPT), the virosome size distribution resembled that seen by cryo-electron microscopy, but dynamic light scattering showed much larger particles. These differences were caused by small virosome aggregates. Measured by SPT, virosomes were stable for 300 days. 3DPHAD ® incorporation in virosomes could be enhanced by providing the adjuvant from DCPC solubilized stock, but also by adding DMSO dissolved adjuvant to pre-formed virosomes. Virosomes with 0.1 mg/mg of 3D-PHAD®/viral protein from DMSO induced antibody titers similar to those by virosomes containing 0.2 mg/mg of DCPC-solubilized 3D-PHAD®. Conclusions: Stable 3D-PHAD® adjuvanted RSV virosomes can be formulated.

A Novel Virus Causes Scale Drop Disease in Lates calcarifer
Groof, A. ; Guelen, L. ; Deijs, M. ; Wal, Y. van der; Miyata, M. ; Ng, K.S. ; Grinsven, L. van; Simmelink, B. ; Biermann, Y. ; Grisez, L. ; Lent, J.W.M. van; Ronde, A. de; Chang, S.F. ; Schrier, C. ; Hoek, L. - \ 2015
PLoS Pathogens 11 (2015)8. - ISSN 1553-7366
red-sea bream - family iridoviridae - pagrus-major - protein - vaccine
From 1992 onwards, outbreaks of a previously unknown illness have been reported in Asian seabass (Lates calcarifer) kept in maricultures in Southeast Asia. The most striking symptom of this emerging disease is the loss of scales. It was referred to as scale drop syndrome, but the etiology remained enigmatic. By using a next-generation virus discovery technique, VIDISCA-454, sequences of an unknown virus were detected in serum of diseased fish. The near complete genome sequence of the virus was determined, which shows a unique genome organization, and low levels of identity to known members of the Iridoviridae. Based on homology of a series of putatively encoded proteins, the virus is a novel member of the Megalocytivirus genus of the Iridoviridae family. The virus was isolated and propagated in cell culture, where it caused a cytopathogenic effect in infected Asian seabass kidney and brain cells. Electron microscopy revealed icosahedral virions of about 140 nm, characteristic for the Iridoviridae. In vitro cultured virus induced scale drop syndrome in Asian seabass in vivo and the virus could be reisolated from these infected fish. These findings show that the virus is the causative agent for the scale drop syndrome, as each of Koch’s postulates is fulfilled. We have named the virus Scale Drop Disease Virus. Vaccines prepared from BEI- and formalin inactivated virus, as well as from E. coli produced major capsid protein provide efficacious protection against scale drop disease.
Folding of influenza virus hemagglutinin in insect cells is fast and efficient
Li, X. ; Oers, M.M. van; Vlak, J.M. ; Braakman, I. - \ 2015
Journal of Biotechnology 203 (2015). - ISSN 0168-1656 - p. 77 - 83.
disulfide bond formation - endoplasmic-reticulum - quality-control - membrane glycoprotein - expression system - escherichia-coli - calnexin - vaccine - ph - oligomerization
Folding of influenza virus hemagglutinin (HA) in the endoplasmic reticulum has been well defined inmammalian cells. In different mammalian cell lines the protein follows the same folding pathway withidentical folding intermediates, but folds with very different kinetics. To examine the effect of cellularcontext on HA folding and to test to which extent insect cells would support the HA folding process,we expressed HA in Sf9 insect cells. Strikingly, in this invertebrate system HA folded faster and moreefficiently, still via the same folding intermediates as in vertebrate cells. Our results suggest that insectcells provide a highly efficient and effective folding environment for influenza virus HA and the idealproduction platform for HA (emergency) vaccines.
Characterization of apoptosis in PER.C6® batch and perfusion cultures
Mercier, S.M. ; Diepenbroek, B. ; Martens, D.E. ; Wijffels, R.H. ; Streefland, M. - \ 2015
Biotechnology and Bioengineering 112 (2015)3. - ISSN 0006-3592 - p. 569 - 578.
hamster ovary cells - high-level expression - flow-cytometry - line per.c6 - death - adenovirus - dna - vaccine - gene - manufacture
Preventing or delaying cell death is a challenge in mammalian cell cultures for the development and optimization of production processes for biopharmaceuticals. Cell cultures need to be maintained highly viable for extended times in order to reach maximum production yields. Moreover, programmed cell death through apoptosis is often believed to occur without being detected by classical viability measurements. In this study, we characterized cell death in PER.C6® batch and perfusion cultures using three flow cytometry techniques measuring different steps of the apoptosis cascade: DNA fragmentation, caspases activation and phosphatidylserine externalization. We showed that apoptosis is the main pathway of PER.C6® cell death in batch cultures after depletion of main carbon sources. In high cell density perfusion cultures fed at a constant specific perfusion rate, both high viability and very limited apoptosis were observed. When extending this perfusion process far beyond standard operations, cultures were exposed to suboptimal process conditions, which resulted in an increase of apoptotic cell death. Moreover, we showed that the reference viability measurement using trypan blue exclusion properly assesses the level of cell death in PER.C6® cultures. This study is a first step in understanding the mechanisms of PER.C6® cell death, which will be helpful to support applications of the cell line.
A cohort study on Actinobacillus pleuropneumoniae colonisation in suckling piglets
Tobias, T.J. ; Klinkenberg, D. ; Bouma, A. ; Broek, J. van den; Daemen, A.J.J.M. ; Wagenaar, J.A. ; Stegeman, J.A. - \ 2014
Preventive Veterinary Medicine 114 (2014)3-4. - ISSN 0167-5877 - p. 223 - 230.
infection patterns - pigs - antibodies - transmission - efficacy - herds - sows - serotype-2 - hemolysin - vaccine
Actinobacillus pleuropneumoniae causes respiratory disease in pigs and despite the use of preventive measures such as vaccination and antimicrobials clinical outbreaks still occur. At weaning often many piglets are not colonised. If differences in prevalence between litters are large and if factors were known that could explain these differences, this may provide an opportunity to raise groups of A. pleuropneumoniae free piglets. To this end, a cohort study was performed on two endemically infected farrow-to-finish farms. Seventy-six of 133 sows were selected using stratified random selection by parity. Farmers complied with a strict hygiene and animal management protocol to prevent transmission between litters. Tonsil brush and serum samples taken three weeks before parturition were tested for antigen with an apxIVA qPCR and antibodies with Apx and Omp ELISAs, respectively. Three days before weaning tonsil brush samples from all piglets (n = 871) were collected and tested for antigen. Whereas all sows tested positive both in serology tests as well as qPCR, 0.41 of the litters tested fully negative and 0.73 of all piglets tested negative. The proportion of positively tested piglets in positive litters ranged from 0.08-1.0 (median= 0.36). A grouped logistic regression model with a beta binomial distribution of the probability for piglets to become infected was fitted to the data and associations with explanatory variables were explored. To test the possibility that alternatively the clustering was caused by onwards transmission among the piglets, a transmission model was fitted to the data incorporating sow-piglet and piglet-piglet transmission, but this model did not fit better. The results of this study showed that the number of colonised suckling piglets was highly clustered and mainly attributable to the variability of infectiousness of the dam, but no dam related risk factor for colonisation status of litter or piglets within litters could be identified. (C) 2014 Elsevier B.V. All rights reserved.
Immunogenicity of recombinant VP2 proteins of all nive serotypes of African horse sickness virus
Kanai, T. ; Rijn, P.A. van; Maris-Veldhuis, M.A. ; Kaname, Y. ; Athmaram, T.N. ; Roy, P. - \ 2014
Vaccine 32 (2014)39. - ISSN 0264-410X - p. 4932 - 4937.
outer capsid proteins - horsesickness-virus - bluetongue virus - protective efficacy - vaccine - baculovirus - expression - challenge - responses - sheep
African horse sickness (AHS) is an equine disease with a mortality of up to 90% for susceptible horses. The causative agent AHS virus (AHSV) is transmitted by species of Culicoides. AHSV serogroup within the genus Orbivirus of the Reoviridae family consists of nine serotypes that show no or very limited cross-neutralization. Of the seven structural proteins (VP1-VP7) of AHSV, VP2 is the serotype specific protein, and the major target for neutralizing antibodies. In this report, recombinant VP2 proteins of all nine serotypes were expressed individually by the baculovirus expression system and the immunogenicity of each was studied by immunization of guinea pigs with single VP2 as well as with cocktails of VP2 proteins. Homologous neutralizing antibodies measured by 50% plaque reduction assay showed varying degrees (from 37 to 1365) of titers for different VP2 proteins. A low cross-neutralizing antibody titer was found for genetically related AHSV serotypes. Immunization with VP2 cocktails containing equal amounts of each of the VP2 proteins also triggered neutralizing antibodies albeit to lower titers (4-117) to each of the serotypes in the cocktail. This study is a first step to develop a VP2 subunit vaccine for AHS and our results indicate that VP2 subunit vaccines are feasible individually or in a multi-serotype cocktail.
Improved poliovirus d-antigen yields by application of different Vero cell cultivation methods
Thomassen, Y.E. ; Rubingh, O. ; Wijffels, R.H. ; Pol, L.A. van der - \ 2014
Vaccine 32 (2014)24. - ISSN 0264-410X - p. 2782 - 2788.
culture process - rabies virus - vaccine - microcarrier - replication - inhibition - bioreactor - metabolism - growth
Vero cells were grown adherent to microcarriers (Cytodex 1; 3 g L-1) using animal component free media in stirred-tank type bioreactors. Different strategies for media refreshment, daily media replacement (semi-batch), continuous media replacement (perfusion) and recirculation of media, were compared with batch cultivation. Cell densities increased using a feed strategy from 1 × 106 cells mL-1 during batch cultivation to 1.8, 2.7 and 5.0 × 106 cells mL-1 during semi-batch, perfusion and recirculation, respectively. The effects of these different cell culture strategies on subsequent poliovirus production were investigated. Increased cell densities allowed up to 3 times higher d-antigen levels when compared with that obtained from batch-wise Vero cell culture. However, the cell specific d-antigen production was lower when cells were infected at higher cell densities. This cell density effect is in good agreement with observations for different cell lines and virus types. From the evaluated alternative culture methods, application of a semi-batch mode of operations allowed the highest cell specific d-antigen production. The increased product yields that can easily be reached using these higher cell density cultivation methods, showed the possibility for better use of bioreactor capacity for the manufacturing of polio vaccines to ultimately reduce vaccine cost per dose. Further, the use of animal-component-free cell- and virus culture media shows opportunities for modernization of human viral vaccine manufacturing.
Specific Interferon-¿ detection for the diagnosis of previous Q fever
Schoffelen, T. ; Joosten, L.A. ; Herremans, T. ; Haan, A.F.J. ; Ammerdorffer, A. ; Rumke, H.C. ; Wijkmans, C. ; Roest, H.I.J. ; Netea, M.G. ; Meer, J.W. van der; Sprong, T. ; Deuren, M. van - \ 2013
Clinical infectious diseases 56 (2013)12. - ISSN 1058-4838 - p. 1742 - 1751.
coxiella-burnetii infection - follow-up - tuberculosis infection - responses - vaccine - tests - outbreak - assays - cells - gold
BACKGROUND: Current practice for diagnosis of Q fever, caused by the intracellular pathogen Coxiella burnetii, relies mainly on serology and, in prevaccination assessment, on skin tests (STs), which both have drawbacks. In this study, C. burnetii-specific interferon ¿ (IFN-¿) production was used as a new diagnostic tool for previous Q fever, circumventing most of these drawbacks. Our aim was to compare this test to serology and ST. METHODS: One thousand five hundred twenty-five individuals from an endemic area with a risk for chronic Q fever were enrolled. IFN-¿ production was measured after in vitro stimulation of whole blood with C. burnetii antigens. Various formats using different C. burnetii antigens were tested. Serology and ST were performed in all individuals. RESULTS: In all assay formats, C. burnetii-specific IFN-¿ production was higher (P <.0001) in seropositive or ST-positive subjects than in seronegative and ST-negative subjects. Whole blood incubated for 24 hours with C. burnetii Nine Mile showed optimal performance. After excluding subjects with equivocal serology and/or borderline ST results, IFN-¿ production was 449 ± 82 pg/mL in the positive individuals (n = 219) but only 21 ± 3 pg/mL in negative subjects (n = 908). Using Bayesian analysis, sensitivity and specificity (87.0% and 90.2%, respectively) were similar to the combination of serology and ST (83.0% and 95.6%, respectively). Agreement with the combination of serology and ST was moderate (84% concordance; ¿ = 0.542). CONCLUSIONS: Specific IFN-¿ detection is a novel diagnostic assay for previous C. burnetii infection and shows similar performance and practical advantages over serology and ST. Future studies to investigate the clinical value in practice are warranted.
'Schmallenberg virus' - a novel orthobunyavirus emerging in Europe
Beer, M. ; Conraths, F.J. ; Poel, W.H.M. van der - \ 2013
Epidemiology and Infection 141 (2013)1. - ISSN 0950-2688 - p. 1 - 8.
vaccine - infection - akabane - cattle
In 2011, a novel orthobunyavirus of the Simbu serogroup, the Schmallenberg virus (SBV), was discovered using a metagenomic approach. SBV caused a large epidemic in Europe in ruminants. As with related viruses such as Akabane virus, it appears to be transmitted by biting midges. Transplacental infection often results in the birth of malformed calves, lambs and goat kids. In more than 5000 farms in Germany, The Netherlands, Belgium, France, UK, Italy, Spain, Luxembourg, Denmark and Switzerland acute infections of adult ruminants or malformed SBV-positive offspring were detected, and high seroprevalences were seen in adult ruminants in the core regions in The Netherlands, Germany and Belgium. The discovery of SBV, the spread of the epidemic, the role of vectors, the impact on livestock, public health issues, SBV diagnosis and measures taken are described in this review. Lessons to be learned from the Schmallenberg virus epidemic and the consequences for future outbreaks are discussed.
Structural perturbation of diphtheria toxoid upon adsorption to aluminium hydroxide adjuvant
Regnier, M. ; Metz, B. ; Tilstra, W. ; Hendriksen, C. ; Jiskoot, W. ; Norde, W. ; Kersten, G. - \ 2012
Vaccine 30 (2012)48. - ISSN 0264-410X - p. 6783 - 6788.
quality-control - fluorescence spectroscopy - secondary structures - membrane insertion - crystal-structure - protein antigens - salt adjuvants - animal use - vaccine - toxin
Aluminium-containing adjuvants are often used to enhance the potency of vaccines. In the present work we studied whether adsorption of diphtheria toxoid to colloidal aluminium hydroxide induces conformational changes of the antigen. Diphtheria toxoid has a high affinity for the aluminium hydroxide particles based on a high adsorption degree, adsorption rate and adsorptive capacity. The conformation and stability of diphtheria toxoid in solution and adsorbed to aluminium hydroxide adjuvant were characterized using five physicochemical techniques: intrinsic and extrinsic fluorescence spectroscopy, circular dichroism, infrared spectroscopy and differential scanning calorimetry. Diphtheria toxoid adsorbed to aluminium hydroxide resulted in a minimal shift of the tryptophan fluorescence spectrum, whereas a large increase in the emission of the Bis-ANS probe was observed, indicating that hydrophobic sites of the protein became accessible due to adsorption. In addition, circular dichroism and infrared spectroscopy revealed that adsorption to aluminium hydroxide caused an increase of ß-sheet content and a decrease of a-helix content in diphtheria toxoid. Differential scanning calorimetry demonstrated a major decrease in the enthalpy of denaturation upon adsorption. In conclusion, the adsorption of diphtheria toxoid to aluminium hydroxide adjuvant leads to substantial conformational changes in the antigen. Since physicochemical methods can be used to monitor these conformational changes, these analytical methods might offer a tool in regulatory required vaccine quality control by demonstrating consistency in production.
Mutations in the M-Gene Segment Can Substantially Increase Replication Efficiency of NS1 Deletion Influenza A Virus in MDCK Cells
Wielink, R. van; Harmsen, M.M. ; Martens, D.E. ; Peeters, B.P.H. ; Wijffels, R.H. ; Moormann, R.J.M. - \ 2012
Journal of Virology 86 (2012)22. - ISSN 0022-538X - p. 12341 - 12350.
interferon antagonist ns1 - messenger-rnas - infected-cells - protein expression - apoptosis - vaccine - translation - activation - domain - vero
Influenza viruses unable to express NS1 protein (delNS1) replicate poorly and induce high amounts of interferon (IFN). They are therefore considered as candidate viruses for live-attenuated influenza vaccines. Their attenuated replication is generally assumed to result from the inability to counter the antiviral host response, as delNS1 viruses replicate efficiently in Vero cells, which lack IFN expression. In this study, delNS1 virus was parallel passaged on IFN competent MDCK cells, which resulted in two strains that were able to replicate to high virus titres in MDCK cells due to adaptive mutations in especially the M-gene segment, but also the NP and NS gene segments. Most notable were clustered U-to-C mutations in the M segment of both strains and clustered A-to-G mutations in the NS segment of one strain, which presumably resulted from host cell mediated RNA editing. The M segment mutations in both strains changed the ratio of M1 to M2 expression, probably by affecting splicing efficiency. In one virus, 2 amino acid substitutions in M1 additionally enhanced virus replication, possibly through changes in the M1 distribution between the nucleus and the cytoplasm. Both adapted viruses induced equal levels of IFN as delNS1 virus. These results show that the increased replication of the adapted viruses is not primarily due to altered IFN induction, but rather related to changes in M1 expression or localization. The mutations identified in this paper may be used to enhance delNS1 virus replication for vaccine production.
Transmission characteristics of low pathogenic avian influenza virus of H7N7 and H5N7 subtypes in layer chickens
Gonzales, J.L. ; Elbers, A.R.W. ; Bouma, A. ; Koch, G. ; Wit, J.J. de; Stegeman, J.A. - \ 2012
Veterinary Microbiology 155 (2012)2-4. - ISSN 0378-1135 - p. 207 - 213.
quantification - infection - vaccine - epidemiology - poultry
Lowpathogenicavianinfluenzavirus (LPAIv) infections of H5 and H7 subtypes in poultry are notifiable to the OIE, hence surveillance programmes are implemented. The rate at which LPAIv strains spread within a flock determines the prevalence of infected birds and the time it takes to reach that prevalence and, consequently, optimal sample size and sampling frequency. The aim of this study was to investigate the transmissioncharacteristics of an H7N7 and an H5N7 LPAIv in layerchickens. Two transmission experiments were performed, which consisted of 30 (first experiment) and 20 (second experiment) pairs of conventional layers, respectively. At the start of the experiments, one chicken per pair was inoculated with LPAIv and the other chicken was contact-exposed. Occurrence of infection was monitored by regularly collecting tracheal and cloacal swab samples, which were examined for the presence of virus RNA by RT-PCR. The results of the test were used to estimate the transmission rate parameter (ß), the infectious period (T) and the basic reproduction ratio (R0). In addition, egg production and virus shedding patterns were quantified. For the H7N7virus, the ß, T and R0 estimates were 0.10 (95% confidence interval (CI): 0.04–0.18) day-1, 7.1 (95% CI: 6.5–7.8) days and 0.7 (95% CI: 0.0–1.7), respectively. With the H5N7virus, only a few inoculated chickens (5 out of 20) became infected and no transmission was observed. This study shows that transmissioncharacteristics of LPAIv strains may vary considerably, which has to be taken into account when designing surveillance programmes.
Effect of thiomersal on dissociation of intact (146S) foot-and-mouth disease virions into 12S particles as assessed by novel ELISAs specific for either 146S or 12S particles
Harmsen, M.M. ; Fijten, H.P.D. ; Westra, D.F. ; Coco-Martin, J.M. - \ 2011
Vaccine 29 (2011)15. - ISSN 0264-410X - p. 2682 - 2690.
domain antibody fragments - whole virus-particles - monoclonal-antibodies - thermal-stability - passive-immunization - international bank - protein subunit - sandwich elisa - field strains - vaccine
Intact (146S) foot-and-mouth disease virions (FMDVs) can dissociate into specific (12S) viral capsid degradation products. Using two single-domain antibody fragments that bind specifically to either 146S or 12S particles we developed two ELISAs for the quantification of these particles in FMDV antigen preparations used for vaccine manufacturing. Only O serotype strains are detected in the 146S specific ELISA whereas strains of most serotypes are detected in the 12S specific ELISA. However, the 146S concentration of A and Asia 1 serotype strains could be measured indirectly using the 12S specific ELISA by prior conversion of 146S into 12S particles by heat treatment. This allowed us to demonstrate that addition of the preservative thiomersal to FMDV antigens stimulates the dissociation into 12S particles of O, A and Asia 1 serotype strains upon prolonged storage at 4 °C. FMDV dissociation is known to result in a strongly reduced immunogenicity, which was experimentally confirmed here. Therefore, we recommend to omit thiomersal from FMD vaccines to increase its shelf life
MDCK cell line with inducible allele B NS1 expression propagates deINS1 inflenza virus to high titres
Wielink, R. van; Harmsen, M.M. ; Martens, D.E. ; Peeters, B.P.H. ; Wijffels, R.H. ; Moormann, R.J.M. - \ 2011
Vaccine 29 (2011)40. - ISSN 0264-410X - p. 6976 - 6985.
protein induces apoptosis - airway epithelial-cells - a virus - gene-expression - infected-cells - interferon - vaccine - rna - systems - ability
Influenza A viruses lacking the gene encoding the non-structural NS1 protein (delNS1) have potential use as live attenuated vaccines. However, due to the lack of NS1, virus replication in cell culture is considerably reduced, prohibiting commercial vaccine production. We therefore established two stable MDCK cell lines that show inducible expression of the allele B NS1 protein. Upon induction, both cell lines expressed NS1 to about 1000-fold lower levels than influenza virus-infected cells. Nevertheless, expression of NS1 increased delNS1 virus titres to levels comparable to those obtained with an isogenic virus strain containing an intact NS1 gene. Recombinant NS1 expression increased the infectious virus titres 244 to 544-fold and inhibited virus induced apoptosis. However, NS1 expression resulted in only slightly, statistically not significant, reduced levels of interferon-ß production. Thus, the low amount of recombinant NS1 is sufficient to restore delNS1 virus replication in MDCK cells, but it remains unclear whether this occurs in an interferon dependent manner. In contrast to previous findings, recombinant NS1 expression did not induce apoptosis, nor did it affect cell growth. These cell lines thus show potential to improve the yield of delNS1 virus for vaccine production.
Classical swine fever virus detection: results of a real-time reverse transcription polymerase chain reaction ring trial conducted in the framework of the European network of excellence for epizootic disease diagnosis and control.
Hoffmann, B. ; Blome, S. ; Bonulauri, P. ; Fernández-Pinero, J. ; Greiser-Wilke, I. ; Haegeman, A. ; Isaksson, M. ; Koenen, F. ; Leblanc, N. ; Leifer, I. ; Potier, M.F. Le; Loeffen, W. ; Rasmussen, T.B. ; Stadejek, T. ; Stahl, K. ; Tignon, M. ; Uttenthal, A. ; Poel, W.H.M. van der - \ 2011
Journal of Veterinary Diagnostic Investigation 23 (2011)5. - ISSN 1040-6387 - p. 999 - 1004.
rt-pcr assay - pestiviruses - validation - infection - virulence - vaccine - taqman - probes - signs - pigs
The current study reports on a real-time reverse transcription polymerase chain reaction (real-time RT-PCR) ring trial for the detection of Classical swine fever virus (CSFV) genomic RNA undertaken by 10 European laboratories. All laboratories were asked to use their routine in-house real-time RT-PCR protocols and a standardized protocol commonly used by the Friedrich-Loeffler-Institute (FLI) on a panel of well-characterized samples. In general, all participants produced results within the acceptable range. The FLI assay, several in-house assays, and the commercial kits had high analytical sensitivity and specificity values. Nevertheless, some in-house systems had unspecific reactions or suboptimal sensitivity with only a single CSFV genotype. Follow-up actions involved either improvement of suboptimal assays or replacement of specific laboratory assays with the FLI protocol, with or without modifications. In conclusion, the ring trial showed reliability of classical swine fever diagnosis on an international level and helped to optimize CSFV-specific RT-PCR diagnostics.
Transmission of classical swine fever virus depends on the clinical course of infection which is associated with high and low level of virus excretion
Weesendorp, E. ; Backer, J.A. ; Stegeman, J.A. ; Loeffen, W.L.A. - \ 2011
Veterinary Microbiology 147 (2011)2-3. - ISSN 0378-1135 - p. 262 - 273.
replication kinetics - pigs - virulence - vaccine - quantification - investigate - antibodies - diagnosis - efficacy - strains
Infection with moderately virulent strains of classical swine fever virus (CSFV) can lead to different courses of disease: either (sub)acute, resulting in death or recovery, or chronic disease. The virus excretion dynamics between these courses are quite dissimilar, but it is not known if this also results in differences in virus transmission. In this study, the excretion and transmission dynamics of the moderately virulent Paderborn strain were studied in 15 one-to-one experiments. In these experiments, a single inoculated pig was housed with a single susceptible contact pig from day 1 post-inoculation (p.i.). Each contact pig that became infected was removed and replaced by a new contact pig at day 17 p.i. and day 26 p.i. Infection of contact pigs was monitored by reverse transcription quantitative real-time PCR on oropharyngeal fluid samples. Five of the inoculated pigs developed the chronic form or died during the acute phase (high excreting pigs), while 10 pigs recovered from the infection (low excreting pigs). In the first contact period, there was no significant difference in virus excretion between the high and low excreting pigs, while in the second and third contact period, high excreting pigs excreted significantly higher quantities of virus. Over the entire study period, the reproduction ratio differed significantly between the high (143 [56.3–373]) and low excreting pigs (23.1 [11.5–45.0]). This indicates the importance of high excreting pigs in transmission of CSFV. Furthermore, this study showed the rate of CSFV infections from a contaminated environment.
TroA of Streptococcus suis is required for manganese acquisition and full virulence
Wichgers Schreur, P.J. ; Rebel, J.M.J. ; Smits, M.A. ; Putten, J.P.M. van; Smith, H.E. - \ 2011
Journal of Bacteriology 193 (2011)19. - ISSN 0021-9193 - p. 5073 - 5080.
pneumococcal surface-antigen - 7 european countries - crystal-structure - diseased pigs - pneumoniae - protein - serotype-2 - infection - vaccine - iron
Streptococcus suis causes infections in pigs and occasionally in humans resulting in 23 manifestations as meningitis, sepsis, arthritis and septic shock. For survival within the 24 host, S. suis requires numerous nutrients including trace metals. Little is known about 25 the specific proteins involved in metal scavenging in S. suis. In this study we evaluated 26 the role of the putative high affinity metal binding lipoprotein TroA in metal acquisition 27 and virulence. A mutant strain deficient in the expression of TroA (¿troA mutant) was 28 constructed. Growth of the ¿troA mutant in Todd-Hewitt broth was similar to wild type 29 growth, however growth of the ¿troA mutant in cation-deprived Todd-Hewitt broth and 30 in porcine serum was strongly reduced compared to growth of wild type bacteria. 31 Supplementing the media with extra manganese but not with magnesium, zinc, copper, 32 nickel or iron restored growth to wild type levels, indicating that TroA is specifically 33 required for growth in environments low in manganese. The ¿troA mutant also showed 34 increased susceptibility to H2O2, suggesting TroA is involved in counteracting oxidative 35 stress. Furthermore, the expression of the troA gene was subject to environmental 36 regulation at the transcript level. In a murine S. suis infection model the ¿troA mutant 37 displayed a non-virulent phenotype. These data indicate that S. suis TroA is involved in 38 manganese acquisition and required for full virulence in mice.
Creation of a Nonspreading Rift Valley Fever Virus
Kortekaas, J.A. ; Oreshkova, N.D. ; Cobos-Jeménez, V. ; Vloet, R.P.M. ; Potgieter, C. ; Moormann, R.J.M. - \ 2011
Journal of Virology 85 (2011)23. - ISSN 0022-538X - p. 12622 - 12630.
north-american mosquitos - mammalian-cells - rna-polymerase - expression - rescue - vaccine - protein - particles - cdna - gene
Rift Valley fever virus (RVFV) is a mosquito-borne zoonotic bunyavirus of the genus Phlebovirus and a serious human and veterinary pathogen. RVFV contains a three-segmented RNA genome, which is comprised of the large (L), medium (M), and small (S) segments. The proteins that are essential for genome replication are encoded by the L and S segments, whereas the structural glycoproteins are encoded by the M segment. We have produced BHK replicon cell lines (BHK-Rep) that maintain replicating L and S genome segments. Transfection of BHK-Rep cells with a plasmid encoding the structural glycoproteins results in the efficient production of RVFV replicon particles (RRPs). To facilitate monitoring of infection, the NSs gene was replaced with an enhanced green fluorescent protein gene. RRPs are infectious for both mammalian and insect cells but are incapable of autonomous spreading, rendering their application outside biosafety containment completely safe. We demonstrate that a single intramuscular vaccination with RRPs protects mice from a lethal dose of RVFV and show that RRPs can be used for rapid virus neutralization tests that do not require biocontainment facilities. The methods reported here will greatly facilitate vaccine and drug development as well as fundamental studies on RVFV biology. Moreover, it may be possible to develop similar systems for other members of the bunyavirus family as well.
Transmission and control of African Horse Sickness in The Netherlands: a model analysis.
Backer, J.A. ; Nodelijk, G. - \ 2011
PLoS One 6 (2011)8. - ISSN 1932-6203
culicoides-variipennis diptera - basic reproduction number - bluetongue virus - ceratopogonidae - simulation - epidemic - efficacy - vaccine - spain
African horse sickness (AHS) is an equine viral disease that is spread by Culicoides spp. Since the closely related disease bluetongue established itself in The Netherlands in 2006, AHS is considered a potential threat for the Dutch horse population. A vector-host model that incorporates the current knowledge of the infection biology is used to explore the effect of different parameters on whether and how the disease will spread, and to assess the effect of control measures. The time of introduction is an important determinant whether and how the disease will spread, depending on temperature and vector season. Given an introduction in the most favourable and constant circumstances, our results identify the vector-to-host ratio as the most important factor, because of its high variability over the country. Furthermore, a higher temperature accelerates the epidemic, while a higher horse density increases the extent of the epidemic. Due to the short infectious period in horses, the obvious clinical signs and the presence of non-susceptible hosts, AHS is expected to invade and spread less easily than bluetongue. Moreover, detection is presumed to be earlier, which allows control measures to be targeted towards elimination of infection sources. We argue that recommended control measures are euthanasia of infected horses with severe clinical signs and vector control in infected herds, protecting horses from midge bites in neighbouring herds, and (prioritized) vaccination of herds farther away, provided that transport regulations are strictly applied. The largest lack of knowledge is the competence and host preference of the different Culicoides species present in temperate regions.
Using mortality data for early detection of Classical Swine Fever in The Netherlands
Backer, J.A. ; Brouwer, H. ; Schaik, G. van; Roermund, H.J.W. van - \ 2011
Preventive Veterinary Medicine 99 (2011)1. - ISSN 0167-5877 - p. 38 - 47.
experimental-infection - antibody-response - weaner pigs - virus - transmission - disease - strategies - epidemics - vaccine - marker
Early detection of the introduction of an infectious livestock disease is of great importance to limit the potential extent of an outbreak. Classical Swine Fever (CSF) often causes non-specific clinical signs, which can take considerable time to be detected. Currently, the disease can be detected by three main routes, that are all triggered by clinical signs. To improve the early detection of CSF an additional program, based on mortality data, aims to routinely perform PCR tests on ear notch samples from herds with a high(er) mortality. To assess the effectiveness of this new early detection system, we have developed a stochastic model that describes the virus transmission within a pig herd, the development of disease in infected animals and the different early detection programs. As virus transmission and mortality (by CSF and by other causes) are different for finishing pigs, piglets and sows, a distinction is made between these pig categories. The model is applied to an extensive database that contains all unique pig herds in The Netherlands, their herd sizes and their mortality reports over the CSF-free period 2001-2005. Results from the simulations suggest that the new early detection system is not effective in piglet sections, due to the high mortality from non-CSF causes, nor in sow sections, due to the low CSF-mortality. In finishing herds, the model predicts that the new early detection system can improve the detection time by two days, from 38 (27-53) days to 36(24-51) days after virus introduction, when assuming a moderately virulent virus strain causing a 50% CSF mortality. For this result up to 5 ear notch samples per herd from 8(0-13) finishing herds must be tested every workday. Detecting a source herd two days earlier could considerably reduce the number of initially infected herds. However, considering the variation in outcome and the uncertainty in some model assumptions, this two-day gain in detection time is too small to demonstrate a substantial effect of the new early detection system based on mortality data. But when the alertness of herd-owners and veterinarians diminishes during long CSF-free periods, the new early detection system might gain in effectiveness. (C) 2010 Elsevier B.V. All rights reserved.
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