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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Eight challenges in modelling infectious livestock diseases
Brooks-Pollock, E. ; Jong, M. de; Keeling, M.J. ; Klinkenberg, D. ; Wood, J.L.N. - \ 2015
Epidemics 10 (2015). - ISSN 1755-4365 - p. 1 - 5.
mouth-disease - great-britain - bovine tuberculosis - virus transmission - avian influenza - dynamic-model - uk foot - cattle - epidemic - impact
The transmission of infectious diseases of livestock does not differ in principle from disease transmission in any other animals, apart from that the aim of control is ultimately economic, with the influence of social, political and welfare constraints often poorly defined. Modelling of livestock diseases suffers simultaneously from a wealth and a lack of data. On the one hand, the ability to conduct transmission experiments, detailed within-host studies and track individual animals between geocoded locations make livestock diseases a particularly rich potential source of realistic data for illuminating biological mechanisms of transmission and conducting explicit analyses of contact networks. On the other hand, scarcity of funding, as compared to human diseases, often results in incomplete and partial data for many livestock diseases and regions of the world. In this overview of challenges in livestock disease modelling, we highlight eight areas unique to livestock that, if addressed, would mark major progress in the area.
Evaluating vaccination strategies to control foot and mouth disease: a model comparison study
Roche, S.E. ; Garner, M.G. ; Sanson, R.L. ; Cook, C. ; Birch, C. ; Backer, J.A. ; Dube, C. ; Patyk, K.A. ; Stevenson, M.A. ; Yu, Z.D. - \ 2015
Epidemiology and Infection 143 (2015)6. - ISSN 0950-2688 - p. 1256 - 1275.
emergency vaccination - simulation-model - epidemic - spread - australia - outbreak
SUMMARY Simulation models can offer valuable insights into the effectiveness of different control strategies and act as important decision support tools when comparing and evaluating outbreak scenarios and control strategies. An international modelling study was performed to compare a range of vaccination strategies in the control of foot-and-mouth disease (FMD). Modelling groups from five countries (Australia, New Zealand, USA, UK, The Netherlands) participated in the study. Vaccination is increasingly being recognized as a potentially important tool in the control of FMD, although there is considerable uncertainty as to how and when it should be used. We sought to compare model outputs and assess the effectiveness of different vaccination strategies in the control of FMD. Using a standardized outbreak scenario based on data from an FMD exercise in the UK in 2010, the study showed general agreement between respective models in terms of the effectiveness of vaccination. Under the scenario assumptions, all models demonstrated that vaccination with 'stamping-out' of infected premises led to a significant reduction in predicted epidemic size and duration compared to the 'stamping-out' strategy alone. For all models there were advantages in vaccinating cattle-only rather than all species, using 3-km vaccination rings immediately around infected premises, and starting vaccination earlier in the control programme. This study has shown that certain vaccination strategies are robust even to substantial differences in model configurations. This result should increase end-user confidence in conclusions drawn from model outputs. These results can be used to support and develop effective policies for FMD control.
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.
Confirmation of spatial patterns and termperature effects in Bluetongue virus serotype-8 transmission in NW-Europe from the 2007 reported case data
Boender, G.J. ; Hagenaars, T.J. ; Elbers, A.R.W. ; Gethmann, J.M. ; Meroc, E. ; Guis, H. ; Koeijer, A.A. de - \ 2014
Veterinary Research 45 (2014). - ISSN 0928-4249 - 10 p.
northern europe - infectious-diseases - epidemic - spread - netherlands - emergence - climate - risk
Two separate analyses were carried out to understand the epidemiology of Bluetongue virus serotype 8 (BTV-8) in 2007 in North West Europe: First, the temporal change in transmission rates was compared to the evolution of temperature during that season. Second, we evaluated the spatio-temporal dynamics of newly reported outbreaks, to estimate a spatial transmission kernel. For both analyses, the approach as used before in analysing the 2006 BTV-8 epidemic had to be adapted in order to take into account the fact that the 2007 epidemic was not a newly arising epidemic, but one advancing from whereto it had already spread in 2006. We found that within the area already affected by the 2006 outbreak, the pattern of newly infected farms in 2007 cannot be explained by between-farm transmission, but rather by local re-emergence of the virus throughout that region. This indicates that persistence through winter was ubiquitous for BTV-8. Just like in 2006, we also found that the temperature at which the infection starts to spread lies close to 15 °C. Finally, we found that the shape of the transmission kernel is in line with the one from the 2006 epidemic. In conclusion, despite the substantial differences between 2006 and 2007 in temperature patterns (2006 featured a heat wave in July, whereas 2007 was more regular) and spatial epidemic extent, both the minimum temperature required for transmission and the transmission kernel were similar to those estimated for the 2006 outbreak, indicating that they are robust properties, suitable for extrapolation to other years and similar regions.
Economic Analysis of HPAI Control in the Netherlands II: Comparison of Control Strategies
Longworth, N.J. ; Mourits, Monique C.M. ; Saatkamp, H.W. - \ 2014
Transboundary and Emerging Diseases 61 (2014)3. - ISSN 1865-1674 - p. 217 - 232.
pathogenic avian influenza - poultry farms - mouth-disease - epidemic - virus - transmission - vaccination - simulation - spread - h7n7
A combined epidemiological-economic modelling approach was used to analyse strategies for highly pathogenic avian influenza (HPAI) control for the Netherlands. The modelling framework used was InterSpread Plus (ISP), a spatially based, stochastic and dynamic simulation model. A total of eight control strategies were analysed, including pre-emptive depopulation and vaccination strategies. The analysis was carried out for three different regions in the Netherlands: high-, medium- and low-density areas (HDA, MDA and LDA, respectively). The analysis included the veterinary impact (e.g. number of infected premises and duration), but was particularly focused on the impact on direct costs (DC) and direct consequential costs. The efficient set of control strategies for HDA and MDA included strategies based on either pre-emptive depopulation only or combined vaccination and pre-emptive depopulation: D2 (pre-emptive depopulation within a radius of 2 km), RV3 + D1 (ring vaccination within a radius of 3 km and additional pre-emptive depopulation within a radius of 1 km) and PV + D1 (preventive vaccination in non-affected HDAs and pre-emptive depopulation within a radius of 1 km in the affected HDA). Although control solely based on depopulation in most cases showed to be effective for LDA, pre-emptive depopulation showed to have an additional advantage in these areas, that is, prevention of 'virus jumps' to other areas. The pros and cons of the efficient control strategies were discussed, for example, public perception and risk of export restrictions. It was concluded that for the Netherlands control of HPAI preferably should be carried out using strategies including pre-emptive depopulation with or without vaccination. Particularly, the short- and long-term implications on export, that is, indirect consequential costs (ICC) and aftermath costs of these strategies, should be analysed further.
Land-Applied Goat Manure as a Source of Human QFever in the Netherlands, 2006–2010
Hermans, C.M.L. ; Jeurissen, L.J.J. ; Hackert, V. ; Hoebe, C. - \ 2014
PLoS ONE 9 (2014)5. - ISSN 1932-6203 - 9 p.
coxiella-burnetii - infection - epidemic - outbreak
Studies have shown a link between Q-fever positive farms (QFPFs) and community cases of human Q-fever. Our study is the first to investigate the potential role of contaminated land-applied manure in human Q-fever, based on a large set of nationwide notification and farm management data. Time between manure application and disease onset in geographically linked notified human cases coincided with the incubation period of Q-fever. Proximity of contaminated land parcels predicted human cases better than proximity of QFPFs (80% vs. 58%, 0–5 km in 2009). Incidence around QFPFs and contaminated land parcels decreased with distance, but not around non-contaminated land parcels. Incidence was higher around contaminated land parcels than non-contaminated land parcels (RR = [10],95%CI = [7], [1]–[14,2]). Our findings deliver evidence that, apart from QFPFs, land-applied contaminated manure may be another source of human Q-fever.
Estimation of the transmission of foot-and-mouth disease virus from infected sheep to cattle
Bravo De Rueda, C. ; Jong, M.C.M. de; Eble, P.L. ; Dekker, A. - \ 2014
Veterinary Research 45 (2014). - ISSN 0928-4249 - 11 p.
between-pen transmission - basic reproduction ratio - swine-fever virus - emergency vaccination - subclinical infection - within-pen - pigs - quantification - excretion - epidemic
The quantitative role of sheep in the transmission of foot-and-mouth disease virus (FMDV) is not well known. To estimate the role of sheep in the transmission of FMDV, a direct contact transmission experiment with 10 groups of animals each consisting of 2 infected lambs and 1 contact calf was performed. Secretions and excretions (oral swabs, blood, urine, faeces and probang samples) from all animals were tested for the presence of FMDV by virus isolation (VI) and/or RT-PCR. Serum was tested for the presence of antibodies against FMDV. To estimate FMDV transmission, the VI, RT-PCR and serology results were used. The partial reproduction ratio R0 p i.e. the average number of new infections caused by one infected sheep introduced into a population of susceptible cattle, was estimated using either data of the whole infection chain of the experimental epidemics (the transient state method) or the final sizes of the experimental epidemics (the final size method). Using the transient state method, R0 p was estimated as 1.0 (95% CI 0.2 - 6.0) using virus isolation results and 1.4 (95% CI 0.3 - 8.0) using RT-PCR results. Using the final size method, R0 p was estimated as 0.9 (95% CI 0.2 - 3.0). Finally, R0 p was compared to the R0’s obtained in previous transmission studies with sheep or cattle only. This comparison showed that the infectivity of sheep is lower than that of cattle and that sheep and cattle are similarly susceptible to FMD. These results indicate that in a mixed population of sheep and cattle, sheep play a more limited role in the transmission of FMDV than cattle.
Future structural developments in Dutch and German livestock production and implications for contagious livestock disease control
Hop, G.E. ; Mourits, M.C.M. ; Oude Lansink, A.G.J.M. ; Saatkamp, H.W. - \ 2014
Technological Forecasting and Social Change 82 (2014). - ISSN 0040-1625 - p. 95 - 114.
classical swine-fever - netherlands - delphi - scenarios - prospects - epidemic - industry - systems - models - spread
The structure of livestock production is subject to driving forces that alter veterinary and economic risks of contagious livestock diseases. Insight into changes in this structure is thus important for veterinary contingency planning. The objective of this paper was to explore changes in future production structure features within the cross-border region of the Netherlands (NL), North Rhine Westphalia (NRW) and Lower Saxony (LS) projected towards 2020 using the Policy Delphi method. Additionally, the findings of this study were elaborated in terms of possible implications for contagious livestock disease introduction, spread and control. Experts expected a sharp reduction in the number of farms, a sharp increase in farm size and regional concentration of livestock production, especially in NL. Increases in cross-border trade were expected, particularly in the pig sector, resulting in intensified mutual cross-border production dependency in most sectors. The cross-border region of NL-NRW-LS becomes, therefore, increasingly a single epidemiological area in which disease introduction is a shared veterinary and, consequently, economic risk. This situation results in increased need for collaboration among NL-NRW-LS to improve the joint prevention and control of contagious livestock diseases. It is concluded that veterinary policy makers should proactively anticipate these future changes in the production structure of livestock.
Proper Quality Control of Formulated Foot-and-Mouth Disease Vaccines in Countries with Prophylactic Vaccination is Necessary
Jamal, S.M. ; Shah, S.I. ; Ali, Q. ; Mehmood, A. ; Afzal, M. ; Dekker, A. - \ 2014
Transboundary and Emerging Diseases 61 (2014)6. - ISSN 1865-1674 - p. 483 - 489.
neutralizing antibody-response - potency tests - cattle - pakistan - serotype - afghanistan - protection - challenge - epidemic - immunity
Vaccination is considered as an important tool to control foot-and-mouth disease (FMD). A good quality vaccine containing relevant serotypes and matching strains is a pre-requisite for vaccination to be effective. The present study investigated the quality of different brands of FMD vaccine available in Pakistan, including three locally produced and two imported products. All the vaccines were found free of bacterial or fungal contamination. No adverse effects were noted in suckling mice and buffalo calves inoculated with the vaccines, showing that the vaccines were sterile and safe. The humoral immune response to the FMD vaccines was determined in buffalo calves for 234 days post-vaccination. Very low humoral immune responses against FMD serotypes O, A and Asia 1 viruses were detected to the locally produced vaccines. The imported vaccines, however, elicited a higher antibody response which persisted for a long period in one of the 2 vaccines. The present study highlights the need of assessing an independent vaccine quality control of finished FMD vaccine products.
Spatial relationships in the Q fever outbreaks 2007–2010 in the Netherlands
Commandeur, M.A.M. ; Jeurissen, L.J.J. ; Hoek, W. van der; Roest, H.I.J. ; Hermans, C.M.L. - \ 2014
International Journal of Environmental Health Research 24 (2014)2. - ISSN 0960-3123 - p. 137 - 157.
epidemic
We analyzed the Q fever epidemic in the Netherlands on a national scale from a spatial point of view. Data on dairy goat farms and Dutch population, whether or not infected, were geo-referenced. Human cases were counted in GIS at different distance classes for all dairy goat farms, farms with Q fever based on BTM analysis, and farms with clinical symptoms. In all selections, human incidence decreased with increasing distances from dairy goat farms. Incidence was highest around farms with clinical symptoms. Depending on the acceptable incidence value, a dairy goat-free zone around residential areas could be defined. Cluster analyses were performed to identify local clusters of both infected farms and human cases and to identify focused clusters of human cases. Focused clusters were detected for only 14 out of 29 farms with clinical symptoms, giving rise to a new hypothesis on the transmission of Q fever
Avian influenza trasnmission risks: analysis of biosecuritiy measures and contact structure in Dutch poultry farming
Ssematimba, A. ; Hagenaars, T.H.J. ; Wit, J.J. de; Ruiterkamp, F. ; Fabri, T.H.F. ; Stegeman, J.A. ; Jong, M.C.M. de - \ 2013
Preventive Veterinary Medicine 109 (2013)1-2. - ISSN 0167-5877 - p. 106 - 115.
potential pathways - virus h7n7 - a viruses - netherlands - epidemic - chickens - georgia - canada - japan
In the 2003 epidemic of highly pathogenic avian influenza in Dutch poultry, between-farm virus transmission continued for considerable time despite control measures. Gaining more insight into the mechanisms of this spread is necessary for the possible development of better control strategies. We carried out an in-depth interview study aiming to systematically explore all the poultry production activities to identify the activities that could potentially be related to virus introduction and transmission. One of the between-farm contact risks that were identified is the movement of birds between farms during thinning with violations of on-farm biosecurity protocols. In addition, several other risky management practices, risky visitor behaviours and biosecurity breaches were identified. They include human and fomite contacts that occurred without observing biosecurity protocols, poor waste management practices, presence of other animal species on poultry farms, and poor biosecurity against risks from farm neighbourhood activities. Among the detailed practices identified, taking cell phones and jewellery into poultry houses, not observing shower-in protocols and the exchange of unclean farm equipment were common. Also, sometimes certain protocols or biosecurity facilities were lacking. We also asked the interviewed farmers about their perception of transmission risks and found that they had divergent opinions about the visitor- and neighbourhood-associated risks. We performed a qualitative assessment of contact risks (as transmission pathways) based on contact type, corresponding biosecurity practices, and contact frequency. This assessment suggests that the most risky contact types are bird movements during thinning and restocking, most human movements accessing poultry houses and proximity to other poultry farms. The overall risk posed by persons and equipment accessing storage rooms and the premises-only contacts was considered to be medium. Most of the exposure risks are considered to be similar for layer and broiler farms. Our results, including those on farmer opinions, are relevant for the communication with farmers and poultry-related businesses about practices and risks. We conclude by providing recommendations for improvement of control strategies.
Rapid generation of replication-deficient monovalent and multivalent vaccines for bluetongue virus: protection against virulent virus challenge in cattle and sheep
Celma, C.C.P. ; Boyce, M. ; Rijn, P.A. van; Eschbaumer, M. ; Wernike, K. ; Hoffmann, B. ; Beer, M. ; Clercq, K. De; Roy, P. - \ 2013
Journal of Virology 87 (2013)17. - ISSN 0022-538X - p. 9856 - 9864.
time rt-pcr - synthetic rna - particles - europe - vaccination - serotype-8 - strains - epidemic - proteins - efficacy
Since 1998, nine of the 26 serotypes of bluetongue virus (BTV) have spread throughout Europe and serotype 8 has suddenly emerged in northern Europe causing considerable economic losses, both direct (mortality and morbidity) but also indirect due to restriction in animal movements. Therefore many new types of vaccines, particularly subunit vaccines, with improved safety and efficacy for a broad range of BTV serotypes are currently being developed by different laboratories. Here we exploited a reverse genetics-based replication-deficient BTV-1 serotype (disabled infectious single cycle, DISC) to generate a series of DISC vaccine strains. Cattle and sheep were vaccinated with these viruses either singly or in cocktail as multivalent vaccine candidate. All vaccinated animals were seroconverted and developed a neutralizing antibody response against their respective serotype. After challenge with the virulent strains at 21 days post vaccination vaccinated animals showed neither any clinical reaction nor viremia. Further, there was no interference in protection with a multivalent preparation of six distinct DISC viruses. These data indicate that a very rapid response vaccine could be developed based on which serotypes are circulating in the population at the time of an outbreak.
Genetic Data Provide Evidence for Wind-Mediated Transmission of Highly Pathogenic Avian Influenza
Ypma, R.J. ; Jonges, M. ; Bataille, A. ; Stegeman, A. ; Koch, G. ; Boven, M. van; Koopmans, M. ; Ballegooijen, W.M. ; Wallinga, J. - \ 2013
The Journal of Infectious Diseases 207 (2013)5. - ISSN 0022-1899 - p. 730 - 735.
outbreak - h5n1 - epidemic - poultry
Outbreaks of highly pathogenic avian influenza in poultry can cause severe economic damage and represent a public health threat. Development of efficient containment measures requires an understanding of how these influenza viruses are transmitted between farms. However, the actual mechanisms of interfarm transmission are largely unknown. Dispersal of infectious material by wind has been suggested, but never demonstrated, as a possible cause of transmission between farms. Here we provide statistical evidence that the direction of spread of avian influenza A(H7N7) is correlated with the direction of wind at date of infection. Using detailed genetic and epidemiological data, we found the direction of spread by reconstructing the transmission tree for a large outbreak in the Netherlands in 2003. We conservatively estimate the contribution of a possible wind-mediated mechanism to the total amount of spread during this outbreak to be around 18%.
Letter: Search for possible additional reservoirs for human Q fever, the Netherlands
Roest, H.I.J. ; Solt, C.B. van; Tilburg, J.J.H.C. ; Klaassen, C.H. ; Hovius, E.K. ; Roest, F.T.F. ; Vellema, P. ; Brom, R. van der; Zijderveld, F.G. van - \ 2013
Emerging Infectious Diseases 19 (2013)5. - ISSN 1080-6040 - p. 834 - 835.
coxiella-burnetii - epidemic - genotype - outbreak
Moral Convictions and Culling Animals: A Survey in the Netherlands
Cohen, N.E. ; Brom, F.W.A. ; Stassen, E.N. - \ 2012
Anthrozoos 25 (2012)3. - ISSN 0892-7936 - p. 353 - 367.
mouth-disease - attitudes - welfare - foot - epidemic - ethics - issues - crisis
In this paper the results are presented of a national survey in the Netherlands. The aim was to identify and describe the convictions about animals that people have in Dutch society and the role of these in judgments on the culling of healthy animals during an animal disease epidemic. A total of 1,999 responses was received and two groups of respondents were distinguished: A profile (50% of the respondents) and B profile (28%). The A profile respondents considered humans to be superior to animals, whereas the B profile respondents considered both to be equal. Both groups were of the opinion that animals have value, that people have a duty to care for and protect all animals, and that all animals have a right to life. These convictions were based on a number of values, such as animal life, the ability of animals to feel pain and emotions (sentience), and the importance of animal species in the ecosystem. The results of a case study suggest that convictions play a role in judgment. More A respondents agreed with the culling of healthy animals during an animal disease epidemic. More B respondents partly (dis)agreed or disagreed with this. Most respondents (A: 81%, B: 61%) agreed with culling to protect human life. The most important argument against culling was the value of animal life. The A respondents rated all arguments against culling significantly lower than did the B respondents.
Implementing a probabilistic definition of freedom from infection to facilitate trade of livestock: Putting theory into praxis for the example of bovine herpes virus-1
Schuppers, M.E. ; Stegeman, J.A. ; Kramps, J.A. ; Stark, K.D.C. - \ 2012
Preventive Veterinary Medicine 105 (2012)3. - ISSN 0167-5877 - p. 195 - 201.
classical swine-fever - united-kingdom - mouth-disease - consequences - switzerland - epidemic - cattle - tests
International trade of livestock and livestock products poses a significant potential threat for spread of diseases, and importing countries therefore often require that imported animals and products are free from certain pathogens. However, absolute freedom from infection cannot be documented, since all test protocols are imperfect and can lead to false-negative results. It is possible instead to estimate the “probability of freedom from infection” and its opposite, the probability of infection despite having a negative test result. These probabilities can be estimated based on a pre-defined target prevalence, known surveillance efforts in the target population and known test characteristics of any pre-export test. Here, calculations are demonstrated using the example of bovine herpes virus-1 (BoHV-1). In a population that recently became free of BoHV-1 without using vaccination, the probability of being infected of an animal randomly selected for trade is 800 per 1 million and this probability is reduced to 64 (95% probability interval PI 6–161) per 1 million when this animal is tested negatively prior to export with a gB-ELISA. In a population that recently became free of BoHV-1 using vaccination, the probability of being infected of an animal randomly selected for trade is 200 per 1 million, and this probability can be reduced to 63 (95% PI 42–87) when this animal is tested negatively prior to export with a gE-ELISA. Similar estimations can be made on a herd level when assumptions are made about the herd size and the intensity of the surveillance efforts. Subsequently, the overall probability for an importing country of importing at least 1 infected animal can be assessed by taking into account the trade volume. Definition of the acceptable level of risk, including the probability of false-negative results to occur, is part of risk management. Internationally harmonized target prevalence levels for the declaration of freedom from infection from selected pathogens provide a significant contribution to the facilitation of international trade of livestock and livestock products by allowing exporting countries to design tailor-made output-based surveillance programs, while providing equivalent guarantees regarding the probability of freedom from infection of the population. Combining this with an approach to assess the overall probability of introducing at least 1 infected animal into an importing country during a defined time interval will help importing countries to achieve their desired level of acceptable risk and will help to assess the equivalence of animal health and food safety standards between trading partners
Bluetongue Viruses Based on Modified-Live Vaccine Serotype 6 with Exchanged Outer Shell Proteins Confer Full Protection in Sheep against Virulent BTV8
Gennip, H.G.P. van; Water, S.G.P. van de; Maris-Veldhuis, M.A. ; Rijn, P.A. van - \ 2012
PLoS ONE 7 (2012)9. - ISSN 1932-6203
functional-characterization - capsid protein - replication - netherlands - expression - particles - infection - epidemic - release - genome
Since 1998, Bluetongue virus (BTV)-serotypes 1, 2, 4, 9, and 16 have invaded European countries around the Mediterranean Basin. In 2006, a huge BT outbreak started after incursion of BTV serotype 8 (BTV8) in North-Western Europe. IN 2008, BTV6 and BTV11 were reported in the Netherlands and Germany, and in Belgium, respectively. In addition, Toggenburg orbivirus (TOV) was detected in 2008 in Swiss goats, which was recognized as a new serotype of BTV (BTV25). The (re-)emergency of BTV serotypes needs a rapid response to supply effective vaccines. Reverse genetics has been developed for BTV1 and more recently also for BTV6. This latter strain, BTV6/net08, is closely related to live-attenuated vaccine for serotype 6 as determined by full genome sequencing. Here, we used this strain as backbone and exchanged segment 2 and 6, respectively Seg-2 (VP2) and Seg-6 (VP5), for those of BTV serotype 1 and 8 using reverse genetics. These so-called ‘serotyped’ vaccine viruses, as mono-serotype and multi-serotype vaccine, were compared for their protective capacity in sheep. In general, all vaccinated animals developed a neutralizing antibody response against their respective serotype. After challenge at three weeks post vaccination with cell-passaged, virulent BTV8/net07 (BTV8/net07/e1/bhkp3) the vaccinated animals showed nearly no clinical reaction. Even more, challenge virus could not be detected, and seroconversion or boostering after challenge was negligible. These data demonstrate that all sheep were protected from a challenge with BTV8/net07, since sheep of the control group showed viremia, seroconversion and clinical signs that are specific for Bluetongue. The high level of cross-protection is discussed.
Rescue of recent virulent and avirulent field strains of Bluetongue virus by reverse genetics
Gennip, H.G.P. van; Water, S.G.P. van de; Potgieter, C.A. ; Wright, I.M. ; Veldman, D. ; Rijn, P.A. van - \ 2012
PLoS ONE 7 (2012)2. - ISSN 1932-6203
protein - europe - replication - trafficking - netherlands - serotype-8 - infection - epidemic - belgium - release
Since 1998, Bluetongue virus (BTV)-serotypes 1, 2, 4, 9, and 16 have invaded European countries around the Mediterranean Basin. In 2006, a huge BT-outbreak started after incursion of BTV-serotype 8 (BTV8) in North-Western Europe. More recently, BTV6 and BTV11 were reported in North-Western Europe in 2008. These latter strains are closely related to live-attenuated vaccine, whereas BTV8 is virulent and can induce severe disease in ruminants, including cattle. In addition, Toggenburg orbivirus (TOV) was detected in 2008 in Swiss goats, which was recognized as a new serotype of BTV (BTV25). The (re) emergency of known and unknown BTV-serotypes needs a rapid response to supply effective vaccines, and research to study this phenomenon. Recently, orbivirus research achieved an important breakthrough by the establishment of reverse genetics for BTV1. Here, reverse genetics for two recent BTV strains representing virulent BTV8 and avirulent BTV6 was developed. For this purpose, extensive sequencing of full-genomes was performed, resulting in the consensus sequences of BTV8/net07 and BTV6/net08. The recovery of 'synthetic BTV', respectively rgBTV8 and rgBTV6, completely from T7-derived RNA transcripts was confirmed by silent mutations by which these 'synthetic BTVs' could be genetically distinguished from wild type BTV, respectively wtBTV6 and wtBTV8. The in vitro and in vivo properties of rgBTV6 or rgBTV8 were comparable to the properties of their parent strains. The asymptomatic or avirulent properties of rgBTV6 and the virulence of rgBTV8 were confirmed by experimental infection of sheep. Reverse genetics of the vaccine-related BTV6 provides a perfect start to develop new generations of BT-vaccines. Reverse genetics of the virulent BTV8 will accelerate research on the special features of BTV8, like transmission by species of Culicoides in a moderate climate, transplacental transmission, and pathogenesis in cattle.
Modelling the wind-borne spread of highly pathogenic avian influenza virus between farms
Ssematimba, A. ; Hagenaars, T.H.J. ; Jong, M. de - \ 2012
PLoS ONE 7 (2012)2. - ISSN 1932-6203
mouth-disease virus - swine-fever virus - livestock buildings - commercial poultry - airborne spread - great-britain - risk-factors - a virus - epidemic - foot
A quantitative understanding of the spread of contaminated farm dust between locations is a prerequisite for obtaining much-needed insight into one of the possible mechanisms of disease spread between farms. Here, we develop a model to calculate the quantity of contaminated farm-dust particles deposited at various locations downwind of a source farm and apply the model to assess the possible contribution of the wind-borne route to the transmission of Highly Pathogenic Avian Influenza virus (HPAI) during the 2003 epidemic in the Netherlands. The model is obtained from a Gaussian Plume Model by incorporating the dust deposition process, pathogen decay, and a model for the infection process on exposed farms. Using poultry- and avian influenza-specific parameter values we calculate the distance-dependent probability of between-farm transmission by this route. A comparison between the transmission risk pattern predicted by the model and the pattern observed during the 2003 epidemic reveals that the wind-borne route alone is insufficient to explain the observations although it could contribute substantially to the spread over short distance ranges, for example, explaining 24% of the transmission over distances up to 25 km.
Interaction effects between sender and receiver processes in indirect transmission of Campylobacter jejuni between broilers.
Bunnik, B.A.D. van; Hagenaars, T.H.J. ; Bolder, N.M. ; Nodelijk, G. ; Jong, M.C.M. de - \ 2012
BMC Veterinary Research 8 (2012). - ISSN 1746-6148
swine-fever virus - drinking-water - netherlands - epidemic - quantification - salmonella - resistance - bacteria - evaluate - design
Background: Infectious diseases in plants, animals and humans are often transmitted indirectly between hosts (or between groups of hosts), i.e. via some route through the environment instead of via direct contacts between these hosts. Here we study indirect transmission experimentally, using transmission of Campylobacter jejuni (C. jejuni) between spatially separated broilers as a model system. We distinguish three stages in the process of indirect transmission; (1) an infectious "sender" excretes the agent, after which (2) the agent is transported via some route to a susceptible "receiver", and subsequently (3) the receiver becomes colonised by the agent. The role of the sender and receiver side (stage 1 and stage 3) was studied here by using acidification of the drinking water as a modulation mechanism. Results: In the experiment one control group and three treatment groups were monitored for the presence of C. jejuni by taking daily cloacal swabs. The three treatments consisted of acidification of the drinking water of the inoculated animals (the senders), acidification of the drinking water of the susceptible animals (the receivers) or acidification of the drinking water of both inoculated and susceptible animals. In the control group 12 animals got colonised out of a possible 40, in each treatment groups 3 animals out of a possible 40 were found colonised with C. jejuni. Conclusions: The results of the experiments show a significant decrease in transmission rate (beta) between the control groups and treatment groups (p <0.01 for all groups) but not between different treatments; there is a significant negative interaction effect when both the sender and the receiver group receive acidified drinking water (p = 0.01). This negative interaction effect could be due to selection of bacteria already at the sender side thereby diminishing the effect of acidification at the receiver side.
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