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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Pooling of genital swabs for detection by PCR of Taylorella equigenitalis, the cause of contagious equine metritis
Mawhinney, I. ; Errington, J. ; Stamper, N. ; Torrens, N. ; Engelsma, M.Y. ; Roest, H.I.J. - \ 2019
Equine Veterinary Journal 51 (2019)2. - ISSN 0425-1644 - p. 227 - 230.
diagnosis - horse - infection - validation

Background: Sets of genital swabs are routinely taken from horses to screen for the presence of Taylorella equigenitalis, the cause of contagious equine metritis. Typically, two to four different sites are swabbed at a time and tested by culture or PCR. Objectives: This study explored the feasibility of pooling these swabs for a single PCR test per animal instead of testing each swab individually. Study design: In vitro. Methods: PCR signal strengths (Ct values) from 149 historical PCR positive genital swabs, together with historical data on the number of swabs in a set expected to be positive, were used to assess the suitability of pooling for screening horses for T. equigenitalis infection in the population at large. Twenty-four sets of four equine genital swabs were tested. The sets were prepared in the laboratory using one or more swabs positive for T. equigenitalis from naturally infected cases. Positive and negative swabs were selected to reflect a typical range of PCR Ct values expected in field cases of T. equigenitalis infection. These pools were tested by an established PCR to assess the impact and suitability of a PCR test on pooled swabs compared to individual swab testing, by comparing the Ct values. Results: Pooling one positive swab with three negative swabs produced a small drop in Ct value but all pools were still clearly positive. Main limitations: Large numbers of field positive horses are not available, but the proof of concept approach with laboratory prepared pools shows the method is applicable to field cases. Conclusions: It was concluded that pooling of swabs would confer no appreciable drop in the ability to detect a positive animal compared to individual swab testing; pooling is therefore a suitable alternative to individual swab testing with reduced costs. The Summary is available in Spanish – see Supporting Information.

Quantitative analysis of the dose–response of white spot syndrome virus in shrimp
Ngo, Thuy T.N. ; Senior, Alistair M. ; Culina, Antica ; Santos, Eduardo S.A. ; Vlak, Just M. ; Zwart, Mark P. - \ 2018
Journal of Fish Diseases 41 (2018)11. - ISSN 0140-7775 - p. 1733 - 1744.
dose–response - infection - meta-analysis - modelling - shrimp - white spot syndrome virus

White spot syndrome virus (WSSV) is an important cause of mortality and economic losses in shrimp farming. Although WSSV-induced mortality is virus dose dependent and WSSV infection does not necessarily lead to mortality, the relationships between virus-particle dose, infection and mortality have not been analysed quantitatively. Here, we explored WSSV dose–response by a combination of experiments, modelling and meta-analysis. We performed dose–response experiments in Penaeus vannamei postlarvae, recorded host mortality and detected WSSV infection. When we fitted infection models to these data, two models—differing in whether they incorporated heterogeneous host susceptibility to the virus or not—were supported for two independent experiments. To determine the generality of these results, we reanalysed published data sets and then performed a meta-analysis. We found that WSSV dose–response kinetics is indeed variable over experiments. We could not clearly identify which specific infection model has the most support by meta-analysis, but we argue that these results also are most concordant with a model incorporating varying levels of heterogeneous host susceptibility to WSSV. We have identified suitable models for analysing WSSV dose–response, which can elucidate the most basic virus–host interactions and help to avoid underestimating WSSV infection at low virus doses.

RNA ‘Information Warfare’ in Pathogenic and Mutualistic Interactions
Chaloner, Thomas ; Kan, Jan A.L. van; Grant-Downton, Robert T. - \ 2016
Trends in Plant Science 21 (2016)9. - ISSN 1360-1385 - p. 738 - 748.
fungus - infection - non-coding RNA - pathogen - resistance

Regulatory non-coding RNAs are emerging as key players in host–pathogen interactions. Small RNAs such as microRNAs are implicated in regulating plant transcripts involved in immunity and defence. Surprisingly, RNAs with silencing properties can be translocated from plant hosts to various invading pathogens and pests. Small RNAs are now confirmed virulence factors, with the first report of fungal RNAs that travel to host cells and hijack post-transcriptional regulatory machinery to suppress host defence. Here, we argue that trans-organism movement of RNAs represents a common mechanism of control in diverse interactions between plants and other eukaryotes. We suggest that extracellular vesicles are the key to such RNA movement events. Plant pathosystems serve as excellent experimental models to dissect RNA ‘information warfare’ and other RNA-mediated interactions.

Discovery, characterization and applications of natural DNA transformation in Streptococcus suis
Zaccaria, E. - \ 2015
Wageningen University. Promotor(en): Jerry Wells, co-promotor(en): Peter van Baarlen. - Wageningen : Wageningen University - ISBN 9789462576056 - 171
streptococcus suis - virulence - pathogenesis - gene expression - direct dna uptake - virulence factors - infection - modeling - virulentie - pathogenese - genexpressie - directe dna-opname - virulente factoren - infectie - modelleren

Streptococcus suis is Gram-positive bacterium and its natural habitat is the upper respiratory tract of pigs, and in particular the tonsils and nasal cavity. Although it is considered to be a normal member of the adult pig microbiome, it can cause serious diseases in pigs and humans. S. suis is in fact one of the most important swine pathogens world-wide, causing a wide variety of diseases in pigs including septicemia, arthritis, endocarditis, and meningitis that leads often to a rapid death within 1-2 days. Although most human infections are considered the consequence of occupational exposure, in the last years the number of human cases has increased and isolates with multi-resistance genes have been isolated. Human infection caused by S. suis are characterized by a similar symptomatology as in pigs. Despite the economic loss in the pork industry due to S. suis infection and its importance as emerging zoonotic agent, experimental studies of S. suis virulence and pathology have been hampered by the lack of efficient methods for genetic transformation and the lack of a simple, cost-effective model to investigate S. suis virulence.

In some streptococcal species, genetic transformation can be carried out very efficiently as these species can be experimentally induced to take-up and recombine homologous extracellular DNA. The discovery of natural competence in some streptococci and the potential of opening up new avenues for genetic analysis of S. suis, was the motivation for investigating natural competence in this important pathogen.

In Chapter 2 we showed that a peptide pheromone induces competence in S. suis. The induction was dependent on ComX, a sigma factor that controls the streptococcal late competence regulon; the SigX-inducing peptide (XIP); and ComR, a regulator of comX. XIP was identified as an N-terminally truncated variant of ComS. This has resulted in the development of a novel methodology that will enable diverse research groups to accelerate discovery of novel features of S. suis ecology and pathology, especially with respect to virulence.

In Chapter 3 we investigated the genetic regulation of competence in S. suis and we provided a hypothetical model of the S. suis transformasome. We verified the essential role of the S. suis major pilin, and CinA for efficient competence development, supporting the notion that our predicted multi-protein transformasome indeed appears to function as described for other streptococci. We have also characterised the differential metabolic states that enable competence, and the metabolic state associated with competence exit (Chapter 4).

In Chapter 5 we investigated for the first time the use a zebrafish larvae model to assess the relative virulence of S. suis strains in porcine infections. Because of its convenience and cost-effectiveness, this model may be used to assay virulence of environmental S. suis strains, in particularly those of clinical relevance to infection of pigs and humans. Furthermore, a large number of bacterial mutants and strains can be screened for their virulence and in vivo pathogenicity, opening up new avenues to investigate the so far undiscovered pathways mediating successful host infection by S. suis.

In Chapter 6 we applied these two innovative methods (the competence system and the zebrafish larval model) to characterize two different two-component systems (TCS) of S. suis. TCS are important players in the regulation of bacterial adaptation to changes in environmental conditions, including those encountered in the host during infection. In this study, we studied the role of the two TCS of S. suis 2 strain S10 in virulence and in the survival of the bacteria in the bloodstream and host tissue.

Chapter 7 summarizes and discusses the key results and the future prospective of the thesis research.

Praktijk past onderzoeksresultaten Green challenge meeldauw gretig toe : onderzoek meeldauwbeheersing wegens succes verbreed
Staalduinen, J. van; Hofland-Zijlstra, J.D. - \ 2015
Onder Glas 12 (2015)4. - p. 36 - 37.
glastuinbouw - meeldauw - plantenziekten - ziektebestrijdende teeltmaatregelen - infectie - controle - systemische werking - vermeerderingsmateriaal - potplanten - resistentieveredeling - landbouwkundig onderzoek - greenhouse horticulture - mildews - plant diseases - cultural control - infection - control - systemic action - propagation materials - pot plants - resistance breeding - agricultural research
Onder de noemer Green Challenge Meeldauw startte vorig jaar een door het Productschap Tuinbouw en bedrijfsleven gefinancierd en door LTO Glaskracht Nederland begeleid masterplan, dat meer inzicht en oplossingen moet bieden bij het voorkomen en bestrijden van echte meeldauw. De aanvankelijke focus op siergewassen is inmiddels verbreed met vruchtgroenten. Onderzoekster Jantineke Hofland-Zijlstra van Wageningen UR Glastuinbouw doet verslag van de voorlopige resultaten.
Mating type and sexual fruiting body of Botrytis elliptica, the causal agent of fire blight in lily
Terhem, R.B. ; Staats, M. ; Kan, J.A.L. van - \ 2015
European Journal of Plant Pathology 142 (2015)3. - ISSN 0929-1873 - p. 615 - 624.
cinerea - leaves - resistance - infection - behavior - system
Botrytis elliptica is a necrotrophic pathogen that specifically infects Lilium species. Previous records show that B. elliptica collected in the field can successfully develop apothecia in vitro, however, there are no formal descriptions of apothecia of B. elliptica. The aim of this study was to analyse the sequence of the mating type loci of B. elliptica and produce apothecia in the laboratory in order to describe their morphology. The sequences of both MAT alleles (MAT1-1 or MAT1-2) of B. elliptica were determined and compared to the sister taxa, Botrytis cinerea and Sclerotinia sclerotiorum. Two strains of each mating type were used in crosses under controlled conditions to produce apothecia. Primordium rupture from sclerotial tissue occurred 74 days after fertilization and a mature apothecium formed within 1 month after rupture. The apothecia are 7 to 12 mm in height with a disk of 3 to 4 mm in diameter and 0.5 to 1 mm in thickness. The apothecial disk is usually umbilicate, depressed to funnel and rounded in shape. The number of apothecia growing on a sclerotium was one to nine. Asci are long, cylindrical with a size of 208¿×¿14 µm, thin walled and bearing eight ascospores. Ascospores are hyaline in colour, ellipsoidal with rounded ends, usually 18 to 24 µm in length and 6 to 10 µm in width (mean 19.5¿×¿8 µm). Ascospores were infectious on lily leaves.
Chikungunya virus non-structural protein 2-mediated host shut-off disables the unfolded protein response
Fros, J.J. ; Major, L.D. ; Scholte, F.E. ; Gardner, J. ; Hemert, M.J. van; Suhrbier, A. ; Pijlman, G.P. - \ 2015
Journal of General Virology 96 (2015)3. - ISSN 0022-1317 - p. 580 - 589.
endoplasmic-reticulum stress - semliki-forest-virus - messenger-rna - mammalian-cells - er stress - translational shutoff - transcription factor - gene-expression - insect cells - infection
The unfolded protein response (UPR) is a cellular defence mechanism against high concentrations of misfolded protein in the endoplasmic reticulum (ER). In the presence of misfolded proteins, ER-transmembrane proteins PERK and IRE1a become activated. PERK phosphorylates eIF2a leading to a general inhibition of cellular translation, whilst the expression of transcription factor ATF4 is upregulated. Active IRE1a splices out an intron from XBP1 mRNA, to produce a potent transcription factor. Activation of the UPR increases the production of several proteins involved in protein folding, degradation and apoptosis. Here, we demonstrated that transient expression of chikungunya virus (CHIKV) (family Togaviridae, genus Alphavirus) envelope glycoproteins induced the UPR and that CHIKV infection resulted in the phosphorylation of eIF2a and partial splicing of XBP1 mRNA. However, infection with CHIKV did not increase the expression of ATF4 and known UPR target genes (GRP78/BiP, GRP94 and CHOP). Moreover, nuclear XBP1 was not observed during CHIKV infection. Even upon stimulation with tunicamycin, the UPR was efficiently inhibited in CHIKV-infected cells. Individual expression of CHIKV non-structural proteins (nsPs) revealed that nsP2 alone was sufficient to inhibit the UPR. Mutations that rendered nsP2 unable to cause host-cell shut-off prevented nsP2-mediated inhibition of the UPR. This indicates that initial UPR induction takes place in the ER but that expression of functional UPR transcription factors and target genes is efficiently inhibited by CHIKV nsP2.
Towards an Integrated Use of Biological Control by Cladosporium cladosporioides H39 in Apple Scab (Venturia inaequalis) Management
Köhl, J. ; Scheer, C. ; Holb, I.J. ; Masny, S. ; Molhoek, W.M.L. - \ 2015
Plant Disease 99 (2015)4. - ISSN 0191-2917 - p. 535 - 543.
potential biocontrol agents - leaf-litter - ascospore production - chaetomium-globosum - pathogen - resistance - antagonism - orchards - fungicides - infection
Apple scab, caused by Venturia inaequalis, is the most important disease in apple production, reducing yield and quality of fruit. Control of apple scab in commercial orchards currently depends on multiple applications of fungicides. The potential of the antagonistic isolate Cladosporium cladosporioides H39, originating from a sporulating colony of V. inaequalis, to control apple scab development was tested in eight trials during 2 years in orchards in Eperjeske (Hungary), Dabrowice (Poland), and Bavendorf (Germany) planted with different cultivars. Treatments were conducted as calendar sprays or after infection periods. Additional trials in an orchard in Randwijk (The Netherlands) focused on the effect of timing of antagonist application before or after infection periods. The overall results of the field trials consistently showed—for the first time—that stand-alone applications of the antagonist C. cladosporioides H39 can reduce apple scab in leaves and fruit. This was demonstrated in an organic growing system as well as in conventional orchards by spray schedules applied during the primary or the summer season. In both systems, the same control levels could be reached as with common fungicide schedules. Efficacies reached 42 to 98% on leaf scab incidence and 41 to 94% on fruit scab. The antagonist was also effective if applied one or even several days (equivalent to approximately 300 to 2,000 degree h) after infection events in several field trials and a trial conducted in Randwijk with single-spray applications at different intervals before or after infection events. Better understanding of the biology of the antagonist will help to further exploit its use in apple scab control
Cell-Free Propagation of Coxiella burnetii Does Not Affect Its Relative Virulence
Kuley, R. ; Smith, H.E. ; Frangoulidis, D. ; Smits, M.A. ; Roest, H.I.J. ; Bossers, A. - \ 2015
PLoS ONE 10 (2015)3. - ISSN 1932-6203 - 16 p.
real-time pcr - q-fever - ethidium monoazide - phase-ii - propidium monoazide - dead cells - t-cells - lipopolysaccharide - infection - strains
Q fever is caused by the obligate intracellular bacterium Coxiella burnetii. In vitro growth of the bacterium is usually limited to viable eukaryotic host cells imposing experimental constraints for molecular studies, such as the identification and characterisation of major virulence factors. Studies of pathogenicity may benefit from the recent development of an extracellular growth medium for C. burnetii. However, it is crucial to investigate the consistency of the virulence phenotype of strains propagated by the two fundamentally different culturing systems. In the present study, we assessed the viability of C. burnetii and the lipopolysaccaride (LPS) encoding region of the bacteria in both culture systems as indirect but key parameters to the infection potential of C. burnetii. Propidium monoazide (PMA) treatment-based real-time PCR was used for enumeration of viable C. burnetii which were validated by fluorescent infectious focus forming unit counting assays. Furthermore, RNA isolated from C. burnetiipropagated in both the culture systems was examined for LPS-related gene expression. All thus far known LPS-related genes were found to be expressed in early passages in both culturing systems indicating the presence of predominantly the phase I form of C. burnetii. Finally, we used immune-competent mice to provide direct evidence, that the relative virulence of different C. burnetii strains is essentially the same for both axenic and cell-based methods of propagation.
Baculovirus-induced tree-top disease: how extended is the role of egt as a gene for the extended phenotype?
Ros, V.I.D. ; Houte, S. van; Hemerik, L. ; Oers, M.M. van - \ 2015
Molecular Ecology 24 (2015)1. - ISSN 0962-1083 - p. 249 - 258.
spodoptera-exigua larvae - udp-glucosyl transferase - escherichia-coli - lepidopteran host - trichoplusia-ni - deletion - nucleopolyhedrovirus - behavior - insect - infection
Many parasites alter host behaviour to enhance their chance of transmission. Recently, the ecdysteroid UDP-glucosyl transferase (egt) gene from the baculovirus Lymantria dispar multiple nucleopolyhedrovirus (LdMNPV) was identified to induce tree-top disease in L. dispar larvae. Infected gypsy moth larvae died at elevated positions (hence the term tree-top disease), which is thought to promote dissemination of the virus to lower foliage. It is, however, unknown whether egt has a conserved role among baculoviruses in inducing tree-top disease. Here, we studied tree-top disease induced by the baculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV) in two different host insects, Trichoplusia ni and Spodoptera exigua, and we investigated the role of the viral egt gene therein. AcMNPV induced tree-top disease in both T. ni and S. exigua larvae, although in S. exigua a moulting-dependent effect was seen. Those S. exigua larvae undergoing a larval moult during the infection process died at elevated positions, while larvae that did not moult after infection died at low positions. For both T. ni and S. exigua, infection with a mutant AcMNPV lacking egt did not change the position where the larvae died. We conclude that egt has no highly conserved role in inducing tree-top disease in lepidopteran larvae. The conclusion that egt is a ‘gene for an extended phenotype’ is therefore not generally applicable for all baculovirus–host interactions. We hypothesize that in some baculovirus–host systems (including LdMNPV in L. dispar), an effect of egt on tree-top disease can be observed through indirect effects of egt on moulting-related climbing behaviour.
Transmission of white spot syndrome virus (WSSV) from Dendronereis spp. (Peters) (Nereididae) to penaeid shrimp
Haryadi, D. ; Verreth, J.A.J. ; Verdegem, M.C.J. ; Vlak, J.M. - \ 2015
Journal of Fish Diseases 38 (2015). - ISSN 0140-7775 - p. 419 - 428.
litopenaeus-vannamei - viral accommodation - baculovirus wsbv - scylla-serrata - mud crab - monodon - pathogenicity - host - infection - virulence
Dendronereis spp. (Peters) (Nereididae) is a common polychaete in shrimp ponds built on intertidal land and is natural food for shrimp in traditionally managed ponds in Indonesia. White spot syndrome virus (WSSV), an important viral pathogen of the shrimp, can replicate in this polychaete (Desrina et al. ); therefore, it is a potential propagative vector for virus transmission. The major aim of this study was to determine whether WSSV can be transmitted from naturally infected Dendronereis spp. to specific pathogen-free (SPF) Pacific white shrimp Litopenaeus vannamei (Boone) through feeding. WSSV was detected in naturally infected Dendronereis spp. and Penaeus monodon Fabricius from a traditional shrimp pond, and the positive animals were used in the current experiment. WSSV-infected Dendronereis spp. and P. monodon in a pond had a point prevalence of 90% and 80%, respectively, as measured by PCR. WSSV was detected in the head, gills, blood and mid-body of Dendronereis spp. WSSV from naturally infected Dendronereis spp was transmitted to SPF L. vannamei and subsequently from this shrimp to new naïve-SPF L. vannamei to cause transient infection. Our findings support the contention that Dendronereis spp, upon feeding, can be a source of WSSV infection of shrimp in ponds.
Schmallenberg Virus in Culicoides Biting Midges in the Netherlands in 2012
Elbers, A.R.W. ; Meiswinkel, R. ; Weezep, E. van; Kooi, E.A. ; Poel, W.H.M. van der - \ 2015
Transboundary and Emerging Diseases 62 (2015)3. - ISSN 1865-1674 - p. 339 - 342.
cattle - surveillance - bluetongue - infection - spp.
A total of 130 pools of Culicoides biting midges collected between May and September 2012 in the Netherlands were assayed for Schmallenberg virus (SBV). The Culicoides midges were caught in the same area as where in 2011 a high proportion of Culicoides pools tested positive for SBV, in majority with a high viral load (Ct values between 20 and 30). Two of a total of 42 pools comprising 50 midges/pool of the Obsoletus complex from the 2012 collection tested weak positive (Ct values: 34.96 and 37.66), indicating a relatively low viral load. On an individual midge level, the proportion of SBV-infected Culicoides of the Obsoletus complex caught in the same area and in a comparable period of the year was significantly lower in 2012 (0.1% = 1 per 1050 tested) compared with 2011 (0.56% = 13 per 2300 tested).
Latest developments on Streptococcus suis: an emerging zoonotic pathogen: part 1
Segura, M. ; Zheng, H. ; Greeff, A. de; Gao, G.F. ; Grenier, D. ; Jiang, Y. ; Chengping, L. ; Maskell, D. ; Oishi, K. ; Okura, M. ; Osawa, R. ; Schultsz, C. ; Schwerk, C. ; Sekizaki, T. ; Smith, H. ; Srimanote, P. ; Takamatsu, D. ; Tang, J. ; Tenenbaum, T. ; Tharavichitkul, P. ; Hoa, N.T. ; Valentin-Weigand, P. ; Wells, J.M. ; Wertheim, H. ; Zhu, B. ; Xu, J. ; Gottschalk, M. - \ 2014
Future Microbiology 9 (2014)4. - ISSN 1746-0913 - p. 441 - 444.
serotype-2 - thailand - infection - diversity
The first international workshop on Streptococcus suis, which is an important swine pathogen and emerging zoonotic agent, took place in Beijing, jointly organized by the Faculty of Veterinary Medicine, University of Montreal, Canada and the National Institute for Communicable Disease Control and Prevention, China CDC. The aim of the meeting was to gather together, for the first time, more than 80 researchers working on S. suis, from countries including China, Canada, Japan, The Netherlands, Germany, Thailand, the UK and Vietnam. This article, the first of a two-part report on this First International Workshop, reviews current aspects of the epidemiology and population genomics of S. suis, covers public health concerns and discusses questions about S. suis serotyping and molecular diagnostics.
Are the specialized bird ticks, Ixodes arboricola and I. frontalis, competent vectors for Borrelia burgdorferi sensu lato?
Heylen, D. ; Sprong, H. ; Oers, K. van; Fonville, M. ; Leirs, H. ; Matthysen, E. - \ 2014
Environmental Microbiology 16 (2014)4. - ISSN 1462-2912 - p. 1081 - 1089.
lyme-disease spirochete - tit parus-major - ricinus ticks - anaplasma-phagocytophilum - avian reservoir - passerine bird - acari ixodidae - central-europe - turdus-merula - infection
Our study tested whether two European bird-specialized ticks, Ixodes arboricola and I. frontalis, can act as vectors in the transmission cycles of Borrelia burgdorferi s.l. The ticks have contrasting ecologies but share songbird hosts (such as the great tit, Parus major) with the generalist I. ricinus which may therefore act as a bridging vector. In the first phase of the experiment, we obtained Borrelia-infected ornithophilic nymphs by exposing larvae to great tits that had previously been exposed to I. ricinus nymphs carrying a community of genospecies (Borrelia garinii, valaisiana, afzelii, burgdorferi s.s., spielmanii). Skin samples showed that birds selectively amplified B. garinii and B. valaisiana. The spirochetes were transmitted to the ornithophilic ticks and survived moulting, leading to infection rates of 16% and 27% in nymphs of I. arboricola and I. frontalis respectively. In the second phase, pathogen-free great tits were exposed to the Borrelia-infected ornithophilic nymphs. None of these ticks were able to infect the birds, as indicated by the tissue samples. Analysis of xenodiagnostic I. ricinus larvae found no evidence for co-feeding or systemic transmission of B. burgdorferi s.l. These outcomes do not support the occurrence of enzootic cycles of Borrelia burgdorferi s.l. involving songbirds and their specialized ornithophilic ticks.
Post-Travel Screening of Asymptomatic Long-Term Travelers to the Tropics for Intestinal Parasites Using Molecular Diagnostics
Soonawala, D. ; Lieshout, L. ; Boer, M.A.M. den; Claas, E.C.J. ; Verweij, J.J. ; Godkewitsch, A. ; Ratering, M. ; Visser, L.G. - \ 2014
American Journal of Tropical Medicine and Hygiene 90 (2014)5. - ISSN 0002-9637 - p. 835 - 839.
real-time pcr - strongyloides-stercoralis - laboratory tests - fecal samples - netherlands - microscopy - infection - diarrhea - protozoa
The incidence of asymptomatic travel-related parasitic infection is uncertain. Previous studies did not distinguish new incident infections, from past infections. Regardless of symptoms, we performed multiplex real-time polymerase chain reaction on pre- and post-travel stool samples of Dutch long-term travelers to the (sub)tropics. Serological screening for Schistosoma spp. was only performed in travelers to sub-Saharan Africa. In total, 679 travelers were included in the study. The follow-up rate was 82% (556 of 679). Participants' median travel duration was 12 weeks. There was one incident infection with Strongyloides stercoralis; there were none with Entamoeba histolytica, 4 with Cryptosporidium spp. (1%), and 22 with Giardia lamblia (4%). Nine of 146 travelers (6%) seroconverted for Schistosoma spp. Routine screening of stool samples for parasitic infection is not indicated for asymptomatic people, who travel to the (sub)tropics for up to 3 months. Screening for Schistosoma spp. should be offered to travelers with fresh-water contact in endemic regions.
Seroprevalence and associated risk factors of important pig viral diseases in Bhutan
Monger, V.R. ; Stegeman, J.A. ; Koop, G. ; Dukpa, K. ; Tenzin, T. ; Loeffen, W.L.A. - \ 2014
Preventive Veterinary Medicine 117 (2014)1. - ISSN 0167-5877 - p. 222 - 232.
classical swine-fever - influenza-a h1n1 - vaccination policy - antigenic drift - virus - infection - diagnosis - prrs
A cross-sectional serological study was conducted in Bhutan between October 2011 and February 2012 to determine the prevalence of antibodies to classical swine fever virus (CSFV), porcine reproductive and respiratory syndrome virus (PRRSV), porcine circovirus type 2 (PCV2), swine influenza virus (SIV) subtype H1N1 and Aujeszky's disease virus (ADV). Furthermore, risk factors for the seropositive status were investigated. Antibodies to SIV, subtype H1N1 (likely pandemic H1N1 2009) were detected in 49% of the pigs in the government farms, and 8% of the village backyard pigs. For PCV2, these percentages were 73% and 37% respectively. For CSFV, the percentages were closer together, with 62% and 52% respectively. It should be taken into consideration that vaccination of piglets is routine in the government herds, and that piglets distributed to backyard farms are also vaccinated. No direct evidence of CSFV infections was found, either by clinical signs or virus isolation. Antibodies to PRRSV and Aujeszky's disease, on the other hand, were not found at all. Risk factors found are mainly related to practices of swill feeding and other biosecurity measures. For CSFV, these were swill feeding (OR = 2.25, 95% CI: 1.01–4.99) and contact with neighbour's pigs (OR = 0.31, 95% CI: 0.13–0.75). For PCV2 this was lending of boars for local breeding purposes (OR = 3.30, 95% CI: 1.43–7.59). The results of this study showed that PCV2 and SIV infections are important in pigs in Bhutan and thus appropriate control strategies need to be designed and applied which could involve strict regulation on the import of live pigs and vaccination against these diseases.
Risk based surveillance for early detection of low pathogenic avian influenza outbreaks in layer chickens
Gonzales, J.L. ; Boender, G.J. ; Elbers, A.R.W. ; Stegeman, J.A. ; Koeijer, A.A. de - \ 2014
Preventive Veterinary Medicine 117 (2014)1. - ISSN 0167-5877 - p. 251 - 259.
transmission characteristics - virus - poultry - epidemic - netherlands - infection - spread - interventions - population - program
Current knowledge does not allow the prediction of when low pathogenic avian influenza virus (LPAIV) of the H5 and H7 subtypes infecting poultry will mutate to their highly pathogenic phenotype (HPAIV). This mutation may already take place in the first infected flock; hence early detection of LPAIV outbreaks will reduce the likelihood of pathogenicity mutations and large epidemics. The objective of this study was the development of a model for the design and evaluation of serological-surveillance programmes, with a particular focus on early detection of LPAIV infections in layer chicken flocks. Early detection is defined as the detection of an infected flock before it infects on average more than one other flock (between-flock reproduction ratio Rf <1), hence a LPAI introduction will be detected when only one or a few other flocks are infected. We used a mathematical model that investigates the required sample size and sampling frequency for early detection by taking into account the LPAIV within- and between-flock infection dynamics as well as the diagnostic performance of the serological test used. Since layer flocks are the target of the surveillance, we also explored whether the use of eggs, is a good alternative to sera, as sample commodity. The model was used to refine the current Dutch serological-surveillance programme. LPAIV transmission-risk maps were constructed and used to target a risk-based surveillance strategy. In conclusion, we present a model that can be used to explore different sampling strategies, which combined with a cost-benefit analysis would enhance surveillance programmes for low pathogenic avian influenza.
Identification and typing of Brucella spp. in stranded harbour porpoises (Phocoena phocoena) on the Dutch coast.
Maio, E. ; Begeman, L. ; Bisselink, Y.J.W.M. ; Tulden, P.W. van; Wiersma, L. ; Hiemstra, S. ; Ruuls, R. ; Gröne, A. ; Roest, H.I.J. ; Willemsen, P.T.J. ; Giessen, J. van der - \ 2014
Veterinary Microbiology 173 (2014)1-2. - ISSN 0378-1135 - p. 118 - 124.
marine mammal brucella - north-sea - adjacent waters - infection - pinnipedialis - ceti - cetaceans - lungworms - emphasis - exposure
The presence of Brucella (B.) spp. in harbour porpoises stranded between 2008 and 2011 along the Dutch coast was studied. A selection of 265 tissue samples from 112 animals was analysed using conventional and molecular methods. In total, 4.5% (5/112) of the animals corresponding with 2.3% (6/265) Brucella positive tissue samples were Brucella positive by culture and these were all confirmed by real-time polymerase chain reaction (real-time PCR) based on the insertion element 711 (IS711). In addition, two more Brucella-positive tissue samples from two animals collected in 2011 were identified using real-time PCR resulting in an overall Brucella prevalence of 6.3% (7/112 animals). Brucella spp. were obtained from lungs (n=3), pulmonary lymph node (n=3) and lungworms (n=2). Multi Locus Variable Number of Tandem Repeats (VNTR) Analysis (MLVA) typing based on the MLVA-16 showed that the Brucella isolates were B. ceti. Additional in silico Multi Locus Sequence typing (MLST) after whole genome sequencing of the 6 Brucella isolates confirmed B. ceti ST 23. According to the Brucella 2010 MLVA database, the isolated Brucella strains encountered were of five genotypes, in two distinct subclusters divided in two different time periods of harbour porpoises collection. This study is the first population based analyses for Brucella spp. infections in cetaceans stranded along the Dutch coast.
Food and environmental routes of Hepatitis E virus transmission
Poel, W.H.M. van der - \ 2014
Current Opinion in Virology 4 (2014). - ISSN 1879-6257 - p. 91 - 96.
non-b-hepatitis - genetic-variability - family hepeviridae - liver sausage - pig-liver - wild boar - non-a - infection - replication - swine
Abstract Hepatitis E virus (HEV), genus Hepevirus, family hepeviridae is a main cause of epidemic hepatitis in developing countries and single cases of hepatitis in higher income countries. There are at least four HEV genotypes which have different epidemiologic and clinical features. Hepatitis E viruses are often transmitted via food and environmental routes. The actual role of these transmission routes in the spread of HEV can depend on the virus genotype, the environmental conditions, the hygienic conditions and the types of foods consumed. In this review food and environmental routes of HEV transmission are discussed to raise the awareness regarding the focal points for the development of accurate prevention and control strategies of HEV infection, food safety and public health protection.
The Schmallenberg virus epidemic in Europe 2011-2013
Afonso, A. ; Abrahantes, J.C. ; Conraths, F. ; Veldhuis, A.E. ; Elbers, A.R.W. - \ 2014
Preventive Veterinary Medicine 116 (2014)4. - ISSN 0167-5877 - p. 391 - 403.
congenital-abnormalities - akabane virus - newborn lambs - infection - cattle - sheep - seroprevalence - outbreaks - france
During the Schmallenberg virus (SBV) epidemic, the European Food Safety Authority (EFSA) collected data on SBV occurrence across Europe in order to provide an assessment of spread and impact. By May 2013, twenty-nine countries were reporting to EFSA and twenty-two countries had reported cases of SBV. The total number of SBV herds reported was 13,846 and the number of SBV laboratory confirmed herds was 8730. The surveillance activities were based on the detection of SBV clinical cases (either adults or newborns). Malformation in newborns was the most commonly reported clinical sign of SBV-infection. All countries were able to provide the date when the first suspicion of SBV in the herd was reported and nineteen could report the location of the herd at a regional level. This allowed the spread of SBV in Europe to be measured both temporally and spatially. The number of SBV confirmed herds started to increase in December 2011 and two peaks were observed in 2012 (February and May). Confirmed herds continued to be reported in 2012 and into 2013. An increase during winter 2012 and spring 2013 was again observed, but the number of confirmed herds was lower than in the previous year. SBV spread rapidly throughout Europe from the initial area of detection. SBV was detected above the latitude of 60° North, which exceeds the northern expansion observed during the bluetongue virus serotype 8 epidemic in 2006-2009. The impact of SBV was calculated as ratio of the number of herds with at least one malformed SBV positive foetus and the total number of herds in this region. The 75th percentile of the malformations ratio in the various affected countries for the whole reporting period was below 1% and 3% for cattle and sheep herds, respectively. International data collection on emerging diseases represents a challenge as the nature of available data, data quality and the proportion of reported cases may vary widely between affected countries. Surveillance activities on emerging animal diseases are often structured only for case detection making the estimation of infection/diseases prevalence and the investigation of risk factors difficult. The impact of the disease must be determined to allow risk managers to take appropriate decisions. Simple within-herd impact indicators suitable for emerging disease outbreaks should be defined that could be measured as part of routine animal health surveillance programmes and allow for rapid and reliable impact assessment of emerging animal health diseases.
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