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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    Behavioural factors of Dutch pig producers related to control of Toxoplasma gondii infections in pigs
    Wagenberg, Coen P.A. Van; Asseldonk, Marcel A.P.M. Van; Bouwknegt, Martijn ; Wisselink, Henk J. - \ 2020
    Preventive Veterinary Medicine 176 (2020). - ISSN 0167-5877
    Toxoplasma gondii (T. gondii) is a food safety hazard which causes a substantial human disease burden. Infected pig meat is a common risk source of toxoplasmosis. Therefore, it is important to control T. gondii infections in pigs. Improving farm management to control the introduction risk likely contributes to that aim. A pig producer only implements control measures when he or she is aware of the underlying problem, wants to solve it, and is able to solve it. If a pig producer is not implementing appropriate control measures, behavioural change interventions can be introduced to overcome constraining behavioural factors. To aid in designing behaviour change interventions, this study analysed behavioural factors of Dutch pig producers in terms of capability, opportunity and motivation to control T. gondii infections in pigs. Key risk sources analysed focused on the life cycle of T. gondii, with cats as primary host, rodents as intermediate host, and uncovered feed as an important risk source. A survey was conducted among Dutch pig producers. Responses were analysed using descriptive and cluster analysis. Results showed that around 80% of the 67 responding pig producers was aware of key risk sources of T. gondii infections in pigs. Respondents also rated risk sources that are not known to increase the risk of T. gondii infections in pigs as somewhat important. Many respondents did not know about potential consequences of a T. gondii infection in pigs on human health. Two third expected some impact on pig performance, which is incorrect because T. gondii generally does not make pigs ill. Most respondents indicated to have the motivation and opportunity to control the risk sources cats, rodents and uncovered feed. Three pig producer clusters were identified: one with higher capability to control rodents, one with lower motivation to control rodents and cats and to cover feed storages, and one with lower scores on the importance of rodent control for pigs, human health and farm profit. We conclude that, although many pig producers have knowledge about risk sources for and consequences of T. gondii infections in pigs, the public health impact and risks of T. gondii infections in pigs are not yet common knowledge among all Dutch pig producers. Furthermore, Dutch pig producers differ in opportunity and motivation to control T. gondii infections. Targeted interventions to address these specific constraining behavioural factors can help to improve the control of T. gondii infections in pigs.
    A risk based surveillance programme for Toxoplasma gondii in pigs using a combination of farm auditing and serological screening
    Wisselink, H.J. ; Swanenburg, M. ; Gonzales Rojas, Jose ; Asseldonk, M.A.P.M. van; Wagenberg, Coen van; Giessen, J. van der; Meerburg, B.G. ; Krijger, Inge ; Eppink, D.M. ; Bouwknegt, M. ; Oorburg, D. - \ 2019
    Toxoplasma gondii is recognized as one of the major foodborne pathogens with a high human disease burden. In the Netherlands, pork contributes to about 11 % of the meatborne T. gondii infections. To control T. gondii infections in pigs, EFSA has advised to perform serological testing of pigs and audits of pig farms on risk factors for T. gondii infection. In the Netherlands, a program was started to translate the EFSA advice into a practical risk based surveillance system. In first instance, a large scale serological monitoring of fattening pigs was started and seroprevalence over time was determined. Next, the association between within-herd seroprevalence and risk factors for T. gondii on fattening pig farms in the Netherlands was determined. For this, a questionnaire for auditing farms for the presence of risk factors of T. gondii was developed and used on 25 case and 50 control farms. Results show that there is a significant association between seroprevalence and risk factors as cats present on farms, use of unheated feed products and feeding wet feed. Moreover, on-farm presence of rats and mice also increases Toxoplasma transmission risks. Subsequently, a study was started on farms to quantify the effectiveness of interventions on farms. A cross-over clinical trial was set up in which case farms were their own control and the cross-over moment is the implementation of interventions on risk factors to change farm management. Farms with a high within-herd seroprevalence were followed for at least during a year and monitored periodically for seroprevalence and implementation of interventions to eventually reduce the disease burden. The break-even point was calculated for which the intervention cost at fattening pig farms equal averted human disease burden and averted cost-of-illness minus cost of the surveillance program. The results shows favourable economic perspectives for interventions to control pig meat-born transmission of T. gondii.
    Identification of potential risk factors for Toxoplasma gondii in fattening pigs in the Netherlands using a Bayesian approach
    Eppink, D.M. ; Bouwknegt, M. ; Oorburg, D. ; Urlings, H.A.P. ; Asseldonk, Marcel van; Wagenberg, Coen van; Krijger, Inge ; Giessen, J.W.P. van der; Swanenburg, M. ; Wisselink, H.J. - \ 2019
    Toxoplasma gondii is a relevant foodborne pathogen,it is estimated that up to one third of the worldpopulation has been exposed to the parasite (Tenteret al. 2000). In the Netherlands toxoplasmosis rankssecond on a list of prioritized emerging zoonosis(Havelaar et al. 2010) and also second in disease burden among 14 foodborne diseases (Mangen et al.2017). Data suggest that ingesting improperly cooked meat containing T. gondii is one of the major sources of infection in Europe and North America (Crotta et al. 2017; Guo et al. 2015). The contribution of pork to meatborne T. gondii infections is estimated to be11 % in the Netherlands (Opsteegh 2011) and is seen as an important possible source of human T. gondii infections (Foroutan et al. 2019). The European Food Safety Authority (EFSA) advised to perform serological testing of pigs and on farm audits on risk factors (EFSA 2011). To that end, a serological monitoring program was developed in a slaughterhouse in the Netherlands. In this study, the objective is to determine the association between within herd seroprevalence, corrected for misclassification of samples through Bayesian analyses, and risk factors for T. gondii on fattening pig farms in TheNetherlands.
    Materials and MethodsFrom 2015 to 2018, HACCP based audits were performedon 75 fattening pig farms in The Netherlands to identify the presence of potential T. gondii risk factors. All farms were conventional pig farms, with 15 farms being farrow to finish. As overall seroprevalence of T. gondii in pigs in the Netherlands is low, estimated at 5 % (1-12 % 95 % CI) by Foroutanet al. 2019, approached farms were chosen with the knowledge of previous serology data. In this way there would be farms with positive serum samples and farms without them included in the study. The audits were based on an updated version of the questionnaire from Mul et al. (2015) and covered the following topics: outdoor access, farm biosecurity, rodent control, presence of cats, feed and watersupply. In addition, serum samples (n=6272) from fattening pigs were obtained at slaughter throughout the year before the audit on the farm was performed. These samples were used for antibody testing bya PrioCHECK™ Toxoplasma Antibody ELISA. Data were analysed using Bayesian statistics, with the within farm T. gondii prevalence as dependent variable and potential risk factors as independent variables. As always with serology, misclassification due to false-positive or false-negative results can occur. Statistical methods have been developed to account for such misclassification, based on frequentistic as well as Bayesian approaches (Hui & Walter 1980; Josephet al. 1995). First, all independent variables wereanalysed in a univariate logistic model, and variables with a probability ≤0.25 that zero is included in the 95 % interval were analysed in a multivariable model. The multivariate logistic model was fitted using backward elimination until all remaining variables showed a probability ≤0.05 that zero is included in the 95 % interval. Two-way interaction terms were evaluated similarly to the main variables regarding statistical significance.
    ResultsDescriptive results showed that 50 out of the 75 farms had 1 or more positive serum samplein the year before the audit was performed. In total 438 samples were positive out of the 6272 samples. Final Bayesian analyses are currently being conducted. However, preliminary results from data analysis using frequentistic logistic multivariate regression identified two significant risk factors: the accessibility of pig feed for cats and theprovision of well water as drinking water for the pigs (Table 1).
    Discussion and ConclusionsThe use of serological testing seems to be a valuable guide and monitoring tool for the control of T.gondii in pork production. In a preliminary analysis, a higher within-herd T. gondii seroprevalence on fattening pig farms in the Netherlands was associated with the accessibility of pig feed for cats and the provision of well water as drinking water for the pigs. Improvements in farm management on fattening pig farms will likely contribute to reduction of the human disease burden and is presently studied.
    Large-scale serological screening of slaughter pigs for Toxoplasma gondii infections in The Netherlands during five years (2012-2016): Trends in seroprevalence over years, seasons, regions and farming systems
    Swanenburg, M. ; Gonzales Rojas, Jose ; Bouwknegt, M. ; Boender, G.J. ; Oorburg, D. ; Heres, L. ; Wisselink, H.J. - \ 2019
    Veterinary Parasitology 2 (2019). - ISSN 0304-4017
    Toxoplasma gondii is the causative agent of the parasitic disease toxoplasmosis, which is an important foodborne zoonosis. Eating undercooked meat of infected animals, including pigs, has been considered the major transmission route of T. gondii to humans. Therefore, it is urgent to develop and implement intervention measures in the pork meat chain to reduce risks of acquiring a T. gondii infection. Proposed measures for control of T. gondii in pigs include serological testing of pigs and audits of pig farms on risk factors for T. gondii infection. So far, these ideas have not been tested in practice. In order to generate knowledge about the epidemiology and seroprevalence of T. gondii, as a basis for developing a surveillance system, we studied the long term seroprevalence over years, farming systems and regions, and seasonal patterns of T. gondii seroprevalence in Dutch slaughter pigs. During a five year study period from 2012 to 2016, serum samples were routinely collected in five Dutch pig slaughterhouses. The sera were tested in an ELISA for the presence of antibodies against Toxoplasma. In total 226,340 serum samples were collected and tested during the study period. The observed seroprevalence varied over years, with the highest overall seroprevalence in 2014 (2.8%) and the lowest in 2016 (1.4%). A higher seroprevalence was observed in pigs from organic farms compared to pigs from conventional farms. The overall risk of infection was on average 2.63 times significantly (p < 0.001) higher for organically raised pigs than for conventionally raised pigs. A seasonal pattern in seroprevalence was observed: the results showed a dominant annual periodicity with a seroprevalence peak in winter around week 1 and a minimum seroprevalence in summer around week 27. To our knowledge, this is the first large scale study on the seroprevalence of T. gondii in slaughter pigs. In comparison to other European serological studies, the observed seroprevalence seems to be relatively low. However, care is needed when comparing the results with other studies because of differences in test setup, the number of samples and time period of sampling. The results can be used as a starting point for developing a surveillance system for T. gondii, and for implementation of intervention measures.
    Association between within-herd seroprevalence and risk factors for Toxoplasma gondii in fattening pigs in the Netherlands
    Eppink, D.M. ; Bouwknegt, M. ; Oorburg, D. ; Urlings, H.A.P. ; Asseldonk, Marcel van; Wagenberg, Coen van; Krijger, I.M. ; Giessen, J.W.P. Van der; Swanenburg, M. ; Wisselink, H.J. - \ 2018
    In: Annual General Meeting of the European College of Veterinary Public Health, "Fading of the HACCP after four decades: new trends in VPH for food safety ", Perugia, 17th-19th October 2018. - European College of Veterinary Public Health (ECVPH) - p. 40 - 40.
    Serological screening of Dutch slaughter pigs to estimate the seroprevalence of Toxoplasma gondii infections at farms
    Swanenburg, M. ; Rojas, J.G. ; Bouwknegt, M. ; Oorburg, D. ; Giessen, Joke van der; Wisselink, H.J. - \ 2018
    In: The 15th international symposium of veterinary epidemiology and economics. - Chang Mai, Thailand : The World Organisation for Animal Health (OIE) - p. 252 - 252.
    Knowledge gaps and research priorities in the prevention and control of hepatitis E virus infection
    Poel, W.H.M. Van der; Dalton, H.R. ; Johne, R. ; Pavio, N. ; Bouwknegt, M. ; Wu, T. ; Cook, N. ; Meng, X.J. - \ 2018
    Transboundary and Emerging Diseases 65 (2018)S1. - ISSN 1865-1674 - p. 22 - 29.
    Hepatitis E virus - HEV research priorities - Zoonosis
    Hepatitis E virus (HEV), family Hepeviridae, is a main cause of epidemic hepatitis in developing countries and sporadic and cluster cases of hepatitis in industrialized countries. There are an increasing number of reported cases in humans especially in industrialized countries, and there is a high potential for transboundary spread of zoonotic genotypes of the virus through the transport of pigs, pig products and by-products. Bloodborne transmission of the virus has been reported with a significant medical concern. To better coordinate HEV research and design better control measures of HEV infections in animals, a group of HEV experts reviewed the current knowledge on the disease and considered the existing disease control tools. It was concluded that there is a lack of in-depth information about the spread of the virus from pigs to humans. The role of animals other than pigs in the zoonotic transmission of the virus to humans and the extent of foodborne transmission are poorly understood. Factors involved in development of clinical disease such as infectious dose, susceptibility and virulence of virus strains need to be studied more extensively. However, such studies are greatly hindered by the absence of a broadly applicable, efficient and sensitive in vitro cell culture system for HEV. Diagnostic tools for HEV are available but need to be further validated, harmonized and standardized. Commercially available HEV vaccines for the control of HEV infection in animal populations are needed as such vaccines can minimize the zoonotic risk for humans. Anti-HEV drugs for treatment of HEV-infected patients need to be studied more extensively. The detailed expert review can be downloaded from the project website at
    A summary index for antimicrobial resistance in food animals in the Netherlands
    Havelaar, Arie H. ; Graveland, Haitske ; Kassteele, Jan van de; Zomer, Tizza P. ; Veldman, Kees ; Bouwknegt, Martijn - \ 2017
    BMC Veterinary Research 13 (2017)1. - ISSN 1746-6148 - 1 p.

    BACKGROUND: The Dutch government has set targets for reduction of antimicrobial usage in food animals, stipulating a 50% reduction in usage (on a weight basis) in 2013 as compared to 2009 and a 70% decrease in 2015. A monitoring program has been instituted to evaluate the impact on antimicrobial resistance (AMR). The Dutch Ministry of Public Health Welfare and Sports has expressed the need for a summary index to present the results of the monitoring data concisely to policy makers.

    METHODS: We use data on AMR in bacteria from randomly collected samples from broiler chickens, fattening pigs, veal calves and dairy cows. Escherichia coli was selected for resistance monitoring because they are intrinsically susceptible to the antibiotics included in the test panel (ciprofloxacin, cefotaxime, tetracycline and ampicillin) and they are present in all samples, which facilitates proper randomization and trend analysis. The AMR summary index was calculated for each animal species as a weighted average over the four antibiotics, taking into account their clinical relevance. Weights were obtained by conjoint analysis, a pairwise comparison study involving infectious diseases professionals with clinical and public health backgrounds, with data analysis by conditional logistic regression. The AMR summary index was then computed by Monte Carlo simulation, accounting for sampling and regression uncertainty.

    RESULTS: The highest weights (0.35) were given to ciprofloxacin and cefotaxime followed by ampicillin (0.23) and tetracycline (0.07). Throughout the years, the AMR index was highest in broiler chickens, followed by pigs and veal calves, while the lowest values were consistently recorded in dairy cows. In all animal species, the index in 2014 was significantly lower than in 2009.

    CONCLUSIONS: We demonstrate that high-dimensional data on surveillance of antimicrobial resistance can be summarized in an index for evaluating trends between and within food animal species by a process involving decision makers and scientists to select and weight the most relevant antibiotics.

    Using serological monitoring, internet-based feedback and on-farm auditing to improve Toxoplasma gondii control at Dutch pig farms
    Oorburg, D. ; Eppink, Dorien ; Heijltjes, Janneke ; Bouwknegt, Martijn ; Urlings, Bert ; Giessen, Joke van der; Krijger, Inge ; Mul, Monique ; Swanenburg, M. ; Wisselink, H.J. - \ 2017
    In: 12th International Symposium on the Epidemiology and Control of Biological,Chemical and Physical Hazards in Pigs and Pork - Proceedings Book, Foz doIguaçu, august 21-24, 2017. - Embrapa - p. 201 - 201.
    Toxoplasma gondii is a relevant foodborne pathogen due to its human disease burden. In the Netherlands, pork is estimated to contribute to 11% of the meatborne T. gondii infections. The European Food Safety Authority advised to perform serological testing of pigs and on farm audits on risk factors for T. gondii infection.
    Trends in Salmonella bij de mens, landbouwhuisdieren en in voedsel
    Pelt, W. van; Voort, M. van der; Bouwknegt, M. ; Veldman, K.T. ; Wit, B. ; Heck, M. ; Mughini-Gras, Lapo - \ 2016
    Infectieziekten bulletin 27 (2016)8. - ISSN 0925-711X - p. 243 - 250.
    Sinds het begin van deze eeuw is het aantal patiënten met salmonellose meer dan gehalveerd. Een ontwikkeling die gereflecteerd wordt door de bevindingen in de surveillance van landbouwhuisdieren en van vlees in de winkel, die in dit artikel worden beschreven. De bestrijdingsprogramma’s bij landbouwhuisdieren en verbeteringen in de hygiëne van het voedselproductie proces hebben dus effect gehad. Met een incidentie in de afgelopen 3 jaar van 9,1-9,3 bevestigde salmonellosegevallen per 100.000 inwoners en naar schatting 27.000 gevallen van acute gastro-enteritis door Salmonella-infecties in de bevolking, heeft Nederland een van de laagste incidenties van Europa.
    Tracing enteric viruses in the European berry fruit supply chain
    Maunula, L. ; Kaupke, A. ; Vasickova, P. ; Soderberg, K. ; Kozyra, I. ; Lazic, S. ; Poel, W.H.M. van der; Bouwknegt, M. ; Rutjes, S. ; Willems, K.A. ; Moloney, R. ; Agostino, M. D'; Husman, A.M.D. ; Bonsdorff, C.H. ; Rzezutka, A. ; Pavlik, I. ; Petrovic, T. ; Cook, N. - \ 2013
    International Journal of Food Microbiology 167 (2013)2. - ISSN 0168-1605 - p. 177 - 185.
    hepatitis-e virus - reverse transcription-pcr - time rt-pcr - waste-water - norovirus outbreaks - frozen raspberries - food safety - a virus - transmission - infection
    In recent years, numerous foodborne outbreaks due to consumption of berry fruit contaminated by human enteric viruses have been reported. This European multinational study investigated possible contamination routes by monitoring the entire food chain for a panel of human and animal enteric viruses. A total of 785 samples were collected throughout the food production chain of four European countries (Czech Republic, Finland, Poland and Serbia) during two growing seasons. Samples were taken during the production phase, the processing phase, and at point-of-sale. Samples included irrigation water, animal faeces, food handlers' hand swabs, swabs from toilets on farms, from conveyor belts at processing plants, and of raspberries or strawberries at points-of-sale; all were subjected to virus analysis. The samples were analysed by real-time (reverse transcription, RT)-PCR, primarily for human adenoviruses (hAdV) to demonstrate that a route of contamination existed from infected persons to the food supply chain. The analyses also included testing for the presence of selected human (norovirus, NoV GI, NoV GII and hepatitis A virus, HAV), animal (porcine adenovirus, pAdV and bovine polyomavirus, bPyV) and zoonotic (hepatitis E virus, HEV) viruses. At berry production, hAdV was found in 9.5%, 5.8% and 9.1% of samples of irrigation water, food handlers' hands and toilets, respectively. At the processing plants, hAdV was detected in one (2.0%) swab from a food handler's hand. At point-of-sale, the prevalence of hAdV in fresh raspberries, frozen raspberries and fresh strawberries, was 0.7%, 3.2% and 2.0%, respectively. Of the human pathogenic viruses, NoV GII was detected in two (3.6%) water samples at berry production, but no HAV was detected in any of the samples. HEV-contaminated frozen raspberries were found once (2.6%). Animal faecal contamination was evidenced by positive pAdV and bPyV assay results. At berry production, one water sample contained both viruses, and at point-of-sale 5.7% and 13% of fresh and frozen berries tested positive for pAdV. At berry production hAdV was found both in irrigation water and on food handler's hands, which indicated that these may be important vehicles by which human pathogenic viruses enter the berry fruit chain. Moreover, both zoonotic and animal enteric viruses could be detected on the end products. This study gives insight into viral sources and transmission routes and emphasizes the necessity for thorough compliance with good agricultural and hygienic practice at the farms to help protect the public from viral infections. (C) 2013 Elsevier B.V. All rights reserved.
    Thermal stability of structurally different viruses with proven or potential relevance to food safety
    Tuladhar, E. ; Bouwknegt, M. ; Zwietering, M.H. ; Koopmans, M. ; Duizer, E. - \ 2012
    Journal of Applied Microbiology 112 (2012)5. - ISSN 1364-5072 - p. 1050 - 1057.
    avian influenza-virus - murine norovirus - feline calicivirus - human parechovirus - inactivation - pcr - surface - heat - enteroviruses - disinfection
    Aims: To collect comparative data on thermal stability of structurally different viruses with proven or potential relevance to food safety. Methods and Results: Suspensions with poliovirus Sabin1, adenovirus type5, parechovirus1, human norovirus (NoV) GII.4, murine NoV (MNV1) and human influenza A (H1N1) viruses were heated at 56 and 73°C. Infectivity was tested by culture assay for all but human NoV GII.4 that cannot be cultivated in vitro. Time to first log10 reduction (TFL-value) was calculated based on best fit using the monophasic, biphasic or Weibull models. The Weibull model provided the best fit at 56°C for all viruses except influenza virus. The TFL at 56°C varied between a high of 27 min (parechovirus) to a low of 10 s (adenovirus) and ranked parechovirus > influenza > MNV1 > poliovirus > adenovirus. The monophasic model best described the behaviour of the viruses at 73°C, in which case the TFL was MNV1(62s) > influenza > adenovirus > parechovirus > poliovirus(14s). Conclusions: Viruses do not follow log-linear thermal inactivation kinetics and the thermostability of parechovirus and influenza virus is similar to that of proven foodborne viruses. Significance and Impact of the Study: Resistant fractions of viruses may remain infectious in thermal inactivation processes and inactivation of newly discovered or enveloped viruses in thermal food preparation processes should not be assumed without further testing.
    Estimation of the Likelihood of Fecal-Oral HEV Transmission Among Pigs
    Bouwknegt, M. ; Teunis, P.F.M. ; Frankena, K. ; Jong, M.C.M. de; Rode Husman, A.M. de - \ 2011
    Risk Analysis 31 (2011)6. - ISSN 0272-4332 - p. 940 - 950.
    hepatitis-e-virus - local grocery stores - rt-pcr assay - united-states - experimental-infection - livers sold - sows feces - swine - japan - inactivation
    Sources for human hepatitis E virus (HEV) infections of genotype 3 are largely unknown. Pigs are potential animal reservoirs for HEV. Intervention at pig farms may be desired when pigs are confirmed as a source for human infections, requiring knowledge about transmission routes. These routes are currently understudied. The current study aims to quantify the likelihood of pig feces in causing new HEV infections in pigs due to oral ingestion. We estimated the daily infection risk for pigs by modeling the fate of HEV in the fecal–oral (F–O) pathway. Using parameter values deemed most plausible by the authors based on current knowledge the daily risk of infection was 0.85 (95% interval: 0.03–1). The associated expected number of new infections per day was ~4 (2.5% limit 0.1, the 97% limit tending to infinity) compared to 0.7 observed in a transmission experiment with pigs, and the likelihood of feces causing the transmission approached 1. In alternative scenarios, F–O transmission of HEV was also very likely to cause new infections. By reducing the total value of all explanatory variables by 2 orders of magnitude, the expected numbers of newly infected pigs approached the observed number. The likelihood of F–O transmission decreased by decreasing parameter values, allowing for at most 94% of infections being caused by additional transmission routes. Nevertheless, in all scenarios F–O transmission was estimated to contribute to HEV transmission. Thus, despite the difficulty in infecting pigs with HEV via oral inoculation, the F–O route is likely to cause HEV transmission among pigs.
    Potential role of ticks as vectors of bluetongue virus
    Bouwknegt, C. ; Rijn, P.A. van; Schipper, J.M.J. ; Holzel, D.R. ; Boonstra, J. ; Nijhof, A. ; Rooij, E.M.A. van; Jongejan, F. - \ 2010
    Experimental and Applied Acarology 52 (2010)2. - ISSN 0168-8162 - p. 183 - 192.
    northern europe - ixodid ticks - transmission - infection
    When the first outbreak of bluetongue virus serotype 8 (BTV8) was recorded in North-West Europe in August 2006 and renewed outbreaks occurred in the summer of 2007 and again in 2008, the question was raised how the virus survived the winter. Since most adult Culicoides vector midges are assumed not to survive the northern European winter, and transovarial transmission in Culicoides is not recorded, we examined the potential vector role of ixodid and argasid ticks for bluetongue virus. Four species of ixodid ticks (Ixodes ricinus, Ixodes hexagonus, Dermacentor reticulatus and Rhipicephalus bursa) and one soft tick species, Ornithodoros savignyi, ingested BTV8-containing blood either through capillary feeding or by feeding on artificial membranes. The virus was taken up by the ticks and was found to pass through the gut barrier and spread via the haemolymph into the salivary glands, ovaries and testes, as demonstrated by real-time reverse transcriptase PCR (PCR-test). BTV8 was detected in various tissues of ixodid ticks for up to 21 days post feeding and in Ornithodoros ticks for up to 26 days. It was found after moulting in adult Ixodes hexagonus and was also able to pass through the ovaries into the eggs of an Ornithodoros savignyi tick. This study demonstrates that ticks can become infected with bluetongue virus serotype 8. The transstadial passage in hard ticks and transovarial passage in soft ticks suggest that ticks have potential vectorial capacity for bluetongue virus. Further studies are required to investigate transmission from infected ticks to domestic livestock. This route of transmission could provide an additional clue in the unresolved mystery of the epidemiology of Bluetongue in Europe by considering ticks as a potential overwintering mechanism for bluetongue virus.
    Hepatitis E virus infections in pigs : transmission dynamics and human exposure
    Bouwknegt, M. - \ 2009
    Wageningen University. Promotor(en): Mart de Jong; Wim van der Poel, co-promotor(en): A.M. de Roda Husman. - [S.l. : S.n. - ISBN 9789085855194 - 150
    varkens - hepatitis e-virus - ziekteoverdracht - zoönosen - ziekteprevalentie - blootstelling - ziekten overgebracht door voedsel - volksgezondheid - pigs - hepatitis e virus - disease transmission - zoonoses - disease prevalence - exposure - foodborne diseases - public health
    In dit promotieonderzoek is de transmissie dynamiek van Hepatitis E virus (HEV) bij varkens onderzocht, alsmede de potentiële blootstelling van de Nederlandse bevolking aan HEV uit varkens. Om te onderzoeken of HEV spreidt onder varkens is een experiment opgezet bestaande uit 10 infectieketens. Elke keten bestond uit één intraveneus geïnfecteerd varken ( iv‐varkens) en drie HEV‐gevoelige varkens (contactvarkens). Aan elk van de 10 iv‐varkens is een HEV‐naïef varken blootgesteld (één‐op‐één blootstelling). Indien dit naïeve varken werd geïnfecteerd, werd een volgend HEV‐naïef varken uit de keten aan het zojuist geïnfecteerde varken blootgesteld.
    The course of hepatitis E virus infection in pigs after contact-infection and intravenous inoculation
    Bouwknegt, M. ; Rutjes, S.A. ; Reusken, C.B.E.M. ; Stockhofe-Zurwieden, N. ; Frankena, K. ; Jong, M.C.M. de; Roda Husman, A.M. de; Poel, W.H.M. van der - \ 2009
    BMC Veterinary Research 5 (2009). - ISSN 1746-6148 - 12 p.
    rt-pcr assay - swine - netherlands - transmission - hev - liver - serum - exposure - japan - risk
    Background - Worldwide, hepatitis E virus (HEV) genotype 3 is observed in pigs and transmission to humans is implied. To be able to estimate public health risks from e.g. contact with pigs or consumption of pork products, the transmission routes and dynamics of infection should be identified. Hence, the course of HEV-infection in naturally infected pigs should be studied. Results - To resemble natural transmission, 24 HEV-susceptible pigs were infected either by one-to-one exposure to intravenously inoculated pigs (C1-pigs; n = 10), by one-to-one exposure to contact-infected pigs (C2-pigs: n = 7; C3-pigs: n = 5) or due to an unknown non-intravenous infection route (one C2-pig and one C3-pig). The course of HEV-infection for contact-infected pigs was characterized by: faecal HEV RNA excretion that started at day 7 (95% confidence interval: 5¿10) postexposure and lasted 23 (19¿28) days; viremia that started after 13 (8¿17) days of faecal HEV RNA excretion and lasted 11 (8¿13) days; antibody development that was detected after 13 (10¿16) days of faecal HEV RNA excretion. The time until onset of faecal HEV RNA excretion and onset of viremia was significantly shorter for iv-pigs compared to contact-infected pigs, whereas the duration of faecal HEV RNA excretion was significantly longer. At 28 days postinfection HEV RNA was detected less frequently in organs of contact-infected pigs compared to iv-pigs. For contact-infected pigs, HEV RNA was detected in 20 of 39 muscle samples that were proxies for pork at retail and in 4 of 7 urine samples. Conclusion - The course of infection differed between infection routes, suggesting that contact-infection could be a better model for natural transmission than iv inoculation. Urine and meat were identified as possible HEV-sources for pig-to-pig and pig-to-human HEV transmission
    Estimation of hepatitis E virus transmission among pigs due to contact-exposure
    Bouwknegt, M. ; Frankena, K. ; Rutjes, S.A. ; Wellenberg, G.J. ; Roda Husman, A.M. de; Poel, W.H.M. van der; Jong, M.C.M. de - \ 2008
    Veterinary Research 39 (2008)5. - ISSN 0928-4249 - 11 p.
    transmitted non-a - non-b hepatitis - infectious-diseases - population biology - genetic diversity - rt-pcr - swine - prevalence - antibodies - netherlands
    Locally acquired hepatitis E in humans from industrialized countries has been repeatedly suggested to originate from pigs. Pigs may serve as a reservoir of hepatitis E virus (HEV) for humans when a typical infected pig causes on average more than one newly infected pig, a property that is expressed by the basic reproduction ratio R(0). In this study, R(0) for HEV transmission among pigs was estimated from chains of one-to-one transmission experiments in two blocks of five chains each. Per chain, susceptible first-generation contact pigs were contact-exposed to intravenously inoculated pigs, subsequently susceptible second-generation contact pigs were contact-exposed to infected first-generation contact pigs, and lastly, susceptible third-generation contact pigs were contact-exposed to infected second-generation contact pigs. Thus, in the second and third link of the chain, HEV-transmission due to contact with a contact-infected pig was observed. Transmission of HEV was monitored by reverse transcriptase polymerase chain reaction (RT-PCR) on individual faecal samples taken every two/three days. For susceptible pigs, the average period between exposure to an infectious pig and HEV excretion was six days (standard deviation: 4). The length of HEV-excretion (i.e. infectious period) was estimated at 49 days (95% confidence interval (CI): 17-141) for block 1 and 13 days (95% CI: 11-17) for block 2. The R0 for contact-exposure was estimated to be 8.8 (95% CI: 4-19), showing the potential of HEV to cause epidemics in populations of pigs.
    Bayesian estimation of hepatitis E virus seroprevalence for populations with different exposure levels to swine in The Netherlands
    Bouwknegt, M. ; Engel, B. ; Herremans, M.M.P.T. ; Widdowson, M.A. ; Worm, H.C. ; Koopmans, M.P.G. ; Frankena, K. ; Roda Husman, A.M. de; Jong, M.C.M. de; Poel, W.H.M. van der - \ 2008
    Epidemiology and Infection 136 (2008)4. - ISSN 0950-2688 - p. 567 - 576.
    diagnostic-tests - disease prevalence - gold standard - antibody - veterinarians - specificity - sensitivity - infection - absence - deer
    Hepatitis E virus (HEV) is ubiquitous in pigs worldwide and may be zoonotic. Previous HEV seroprevalence estimates for groups of people working with swine were higher than for control groups. However, discordance among results of anti-HEV assays means that true seroprevalence estimates, i.e. seroprevalence due to previous exposure to HEV, depends on choice of seroassay. We tested blood samples from three subpopulations (49 swine veterinarians, 153 non-swine veterinarians and 644 randomly selected individuals from the general population) with one IgM and two IgG ELISAs, and subsets with IgG and/or IgM Western blots. A Bayesian stochastical model was used to combine results of all assays. The model accounted for imperfection of each assay by estimating sensitivity and specificity, and accounted for dependence between serological assays. As expected, discordance among assay results occurred. Applying the model yielded seroprevalence estimates of ~11% for swine veterinarians, ~6% for non-swine veterinarians and ~2% for the general population. By combining the results of five serological assays in a Bayesian stochastical model we confirmed that exposure to swine or their environment was associated with elevated HEV seroprevalence.
    Hepatitis E Virus RNA in Commercial Porcine Livers in The Netherlands
    Bouwknegt, M. ; Lodder-Verschoor, F. ; Poel, W.H.M. van der; Rutjes, S.A. ; Roda Husman, A.M. de - \ 2007
    Journal of Food Protection 70 (2007)12. - ISSN 0362-028X - p. 2889 - 2895.
    cross-species infection - united-states - phylogenetic analysis - genetic diversity - wild boar - swine - transmission - prevalence - sequences - japan
    Human hepatitis E virus (HEV) infections by genotype 3 strains in industrialized countries are hypothesized to be caused by pigs. To examine this hypothesis, the potential health risks of transmission routes should be examined. Possible foodborne transmission was studied by quantifying the presence and infectivity of HEV in commercial porcine livers in The Netherlands. A comparison of four tissue disruption and seven RNA extraction methods revealed that mechanical disruption followed by silica-based RNA extraction gave the highest RNA yields and was therefore employed on commercial porcine livers. Four (6.5%) of 62 porcine livers were HEV RNA positive by reverse transcriptase PCR and Southern blot hybridization. Each positive liver was estimated to contain ~65 PCR-detectable units per g. Sequences were obtained for three of four positive livers and classified as HEV genotype 3. Ninety-three percent similarity to Dutch human HEV sequences and 97% similarity to Dutch swine HEV sequences were observed. To determine whether positive livers contained infectious HEV particles, extracts from livers with known HEV RNA sequences were inoculated intravenously in pigs. Two control pigs were included: one was inoculated with a high dose known to result in infection (104 PCR-detectable units of HEV RNA), and the other was inoculated with a lower concentration of virus that equaled the concentration of PCR-detectable units in commercial livers (~20 PCR-detectable units). Infection was observed in the high-dose control, but not in other pigs, suggesting a dose-dependent response in pigs. Hence, the implications of HEV RNA in commercial porcine livers in The Netherlands are unknown. However, HEV RNA is present in commercial porcine livers, and sufficient heating of porcine livers before consumption as precautionary measure is recommended.
    Bayesian estimation of the Hepatitis E virus seroprevalence in the Netherlands in populations with different degree of exposure to swine.
    Bouwknegt, M. ; Engel, B. ; Herremans, M.M.P.T. ; Widdowson, M.A. ; Worm, H.C. ; Koopmans, M.P.G. ; Frankena, K. ; Roda Husman, A.M. de; Jong, M.C.M. de; Poel, W.H.M. van der - \ 2007
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