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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Reduced specificity of Erns antibody ELISAs for samples from piglets with maternally derived antibodies induced by vaccination of sows with classical swine fever marker vaccine CP7_E2alf
Meyer, D. ; Loeffen, W. ; Postel, A. ; Fritsche, S. ; Becher, P. - \ 2018
Transboundary and Emerging Diseases 65 (2018)2. - ISSN 1865-1674 - p. e505 - e508.
classical swine fever virus - CP7_E2alf - DIVA assay - E antibody ELISA - marker vaccine - maternally derived antibodies
Successful implementation of marker vaccines against classical swine fever virus is dependent on a reliable accompanying diagnostic assay that allows differentiation of infected from vaccinated animals (DIVA) as well as the development of a testing scheme during emergency vaccination. In this context, special attention needs to be paid to breeding farms, because the offspring of marker vaccinated sows possess maternally derived antibodies (MDAs). So far, limited information is available on the influence of MDAs on serological testing in the context of a DIVA strategy. Therefore, two commercially available Erns antibody ELISAs were compared, using serum samples of piglets with a high-to-moderate titre of MDAs against marker vaccine CP7_E2alf. False-positive results were detected by both Erns antibody ELISAs for serum samples of piglets with an age of up to 4 weeks. Interestingly, most samples tested false-positive in the first Erns antibody ELISA were identified correctly by the other Erns antibody ELISA and vice versa. In conclusion, in case of emergency vaccination of sows, the specificity of both ELISAs in newborn piglets younger than 4 weeks may be relatively low. This could be addressed in a testing strategy by either not sampling piglets up to the age of 4 weeks or using both ELISAs in a screening-confirmation set-up.
Quantification of different classical swine fever virus transmission routes within a single compartment
Weesendorp, E. ; Backer, J. ; Loeffen, W.L.A. - \ 2014
Veterinary Microbiology 174 (2014)3-4. - ISSN 0378-1135 - p. 353 - 361.
between-pen transmission - within-pen - vaccination strategies - experimental-infection - airborne transmission - 1997-1998 epidemic - antibody-response - marker vaccine - low virulence - pigs
During outbreaks of classical swine fever (CSF), CSF virus (CSFV) can be transmitted via different routes. Understanding these transmission routes is crucial in preventing the unlimited spread of the virus in a naïve population, and the subsequent eradication of the virus from that population. The objectives of the present study were to quantify virus transmission within a compartment, differentiating between transmission within a pen, transmission between pens via contact through (open) pen partitions, and transmission via the air. Furthermore, the possible contribution of each of these routes to infection of individual pigs was quantified. A CSFV outbreak was mimicked in a compartment housing 24 pigs in six different pens. Two pigs in one pen were inoculated with the moderately virulent Paderborn strain, and virus transmission to other pigs was followed in time. Virus transmission rates for transmission via the air (ß of 0.33 (0.14–0.64) per day) and transmission between adjacent pens (ß of 0.30 (0–0.88) per day) were comparable, but significantly lower than for virus transmission within a pen (ß of 6.1 (0.86–18) per day). The route via the air created new focal points of infection, from which virus transmission continued through other routes. This shows that, at least within a compartment, transmission via the air is expected to play a relevant role in the fast spread of the virus after an initial slow start. This will have consequences for efficacy of intervention measures, including vaccination during an outbreak.
Time-dependent infection probability of classical swine fever via excretions and secretions
Weesendorp, E. ; Loeffen, W.L.A. ; Stegeman, A. ; Vos, C.J. de - \ 2011
Preventive Veterinary Medicine 98 (2011). - ISSN 0167-5877 - p. 152 - 164.
descriptive epidemiology - neighborhood infections - vaccination strategies - airborne transmission - stochastic simulation - marker vaccine - low virulence - pig herds - virus - netherlands
Several routes contribute to the spread of classical swine fever (CSF) during outbreaks of this disease. However, for many infected herds in recent epidemics, no route of virus introduction could be indentified. To obtain more insight into the relative importance of secretions and excretions in transmission of CSF virus, a model was developed. This model quantified the daily transmission probabilities from one infectious pig to one susceptible pig, using quantitative data on: (a) virus excretion by infected pigs, (b) survival of virus in the environment and (c) virus dose needed to infect susceptible pigs. Furthermore, the model predicted the relative contribution of secretions and excretions to this daily probability of infection of a susceptible pig. Three virus strains that differed in virulence were evaluated with the model: the highly virulent strain Brescia, the moderately virulent strain Paderborn and the low virulent strain Zoelen. Results suggest that it is highly probable that susceptible pigs in contact with Brescia or Paderborn infected pigs will be infected. For a pig in contact with a Zoelen infected pig, infection is less likely. When contact with blood is excluded, the predicted overall probability of infection was only 0.08 over the entire infectious period. The three strains differed in the relative contribution of secretions and excretions to transmission, although blood had a high probability of causing infection of a susceptible pig when in contact with a pig infected with any strain. This supports the statement that during outbreaks, control measures should ideally be based on the characteristics of the specific virus strain involved, which implies the development of strain-specific measures.
Protective efficacy of a Classical swine fever virus C-strain deletion mutant and ability to differentiate invected from vaccinated animals
Kortekaas, J.A. ; Ketelaar, J.H.E. ; Vloet, R.P.M. ; Loeffen, W.L.A. - \ 2011
Veterinary Microbiology 147 (2011)1-2. - ISSN 0378-1135 - p. 11 - 18.
marker vaccine - structural glycoprotein - chimeric pestivirus - pigs - csfv - e2 - virulence - identification - transmission - epitope
Classical swine fever (CSF) continues to be the most economically damaging pig disease in the world. The disease can be effectively controlled by vaccination with the live C-strain vaccine. This vaccine, however, does not enable the serological differentiation between infected and vaccinated animals (DIVA) and its use can therefore impose severe trade restrictions. CSF-specific diagnostic ELISAs detect antibodies directed against the conserved and immunodominant A domain of the E2 structural glycoprotein. We previously reported the production of a C-strain virus in which the immunodominant TAVSPTTLR epitope of the A domain is stably mutated with the aim to render the virus suitable as a DIVA vaccine. We here report that a single vaccination with this vaccine virus protected pigs from a lethal challenge dose of the highly virulent Brescia strain. Analysis of the sera, however, demonstrated that a commercially available E2 ELISA was unsuitable as an accompanying DIVA test.
Seroprevalence and risk factors for the presence of ruminant pestviruses in the Dutch swine population
Loeffen, W.L.A. ; Beuningen, A.R. van; Quak, J. ; Elbers, A.R.W. - \ 2009
Veterinary Microbiology 136 (2009)3-4. - ISSN 0378-1135 - p. 240 - 245.
bovine viral diarrhea - envelope glycoprotein e2 - fever virus csfv - marker vaccine - aujeszkys-disease - hog-cholera - wild boar - serological investigations - cross-neutralization - pigs
Swine can be infected with classical swine fever virus (CSFV), as well as ruminant pestiviruses: bovine viral diarrhoea virus (BVDV), and Border disease virus (BDV). Cross-reactions between pestiviruses occur, both regarding protective immunity and in diagnostic tests. The presence of BVDV and BDV in a swine population may thus affect the transmission of CSFV, but also the diagnosis of a CSFV infection. In this study, the seroprevalence against BVDV and BDV in two categories of swine, sows and finishing pigs, in the Netherlands was determined. Furthermore, several risk factors, associated with the presence of swine and ruminants on the same farm or in the immediate surroundings, were evaluated. In sows, the seroprevalence against BVDV was 2.5% on the animal level, and 11.0% on herd level. In finishing pigs these prevalences were 0.42% and 3.2%, respectively. Antibodies against BDV were found in three sows only. Risk factors, associated with a BVDV-seropositive status in breeding pigs, were the presence of cattle on the same premises and a high density of sheep and/or goats herds in a radius of 3 km. While BVDV and BDV hardly pose any threat to the swine population themselves, knowledge, and therefore regular monitoring, on the presence of these viruses in the swine population is important with respect to CSF eradication. It will allow for a better interpretation of diagnostic test results, both in terms of possible false positives and false negatives, but may also bring about additional measures or surveillance protocols in times of CSF outbreaks to avoid surprises caused by cross-reactivity with ruminant pestiviruses
Modelling the effectiveness and risks of vaccination strategies to control Classical Swine fever epidemics
Backer, J.A. ; Hagenaars, T.H.J. ; Roermund, H.J.W. van; Jong, M.C.M. de - \ 2009
Journal of the Royal Society, Interface 6 (2009)39. - ISSN 1742-5689 - p. 849 - 861.
between-pen transmission - marker vaccine - subunit vaccine - weaner pigs - within-pen - virus - netherlands - quantification - disease - e2
In a recent update of the Dutch contingency plan for controlling outbreaks of classical swine fever (CSF), emergency vaccination is preferred to large-scale pre-emptive culling. This policy change raised two questions: can emergency vaccination be as effective as pre-emptive culling, and what are the implications for showing freedom of infection? Here, we integrate quantitative information available on CSF virus transmission and vaccination effects into a stochastic mathematical model that describes the transmission dynamics at the level of animals, farms and livestock areas. This multilevel approach connects individual-level interventions to large-scale effects. Using this model, we compare the performance of five different control strategies applied to hypothetical CSF epidemics in The Netherlands and, for each of these strategies, we study the properties of three different screening scenarios to show freedom of infection. We find that vaccination in a ring of 2¿km radius around a detected infection source is as effective as ring culling in a 1¿km radius. Feasible screening scenarios, adapted to the use of emergency vaccination, can reduce the enhanced risks of (initially) undetected farm outbreaks by targeting vaccinated farms. Altogether, our results suggest that emergency vaccination against CSF can be equally effective and safe as pre-emptive culling
Comparison of the sensitivity of in vitro and in vivo tests for detection of the presence of a bovine viral diarrhoea virus type 1 strain
Antonis, A.F.G. ; Bouma, A. ; Bree, J. de; Jong, M.C.M. de - \ 2004
Veterinary Microbiology 102 (2004)3-4. - ISSN 0378-1135 - p. 131 - 140.
linked-immunosorbent-assay - fetal protection - glycoprotein e2 - subunit vaccine - pestivirus rna - marker vaccine - cattle - herpesvirus-1 - antibodies - infection
Veterinary vaccines are usually tested for the absence of contaminants. However, the quality control does not always imply that vaccines are not contaminated as, for example, illustrated by the bovine herpes virus 1 (BHV1) vaccine used in The Netherlands in 1999 that contained a small amount of bovine viral diarrhoea virus (BVDV1). Thousands of cows were vaccinated with BHV1 vaccine batches, and the question arose as to whether these small amounts of BVDV1, most likely not detected with in vitro tests, could have infected cattle. More in general, the question was whether the outcome of the in vitro tests, i.e. the in vitro infectivity, was indicative for the infectivity for cattle, i.e. the in vivo infectivity. We therefore carried out in vitro experiments to determine the sensitivity of a BVDV1 isolation assay. In addition, we performed two animal experiments, in which we estimated the lowest dose needed to infect calves with BVDV L We extrapolated the experimental in vitro and in vivo results from a tissue culture infectious dose (TCID50) to a cattle infectious dose (CID50). We observed a partial response in the calves inoculated with this dose: four out of six calves turned out to be infected. In the tissue culture test, all 20 samples tested negative. The response in vivo, however, was not significantly higher than the in vitro response, which implies that no difference in susceptibility was observed between the animal test and the tissue culture test. Based on the results in our experiments, some cattle may have been infected with BVDV1 after the application of the contaminated BHV1 vaccine during the vaccination campaign. The question remains that how many cattle received contaminated vaccine, and became infected with BVDV1. (C) 2004 Elsevier B.V. All rights reserved.
Transmission of bovine herpesvirus 1 within and between herds on an island with a BHV1 control programme
Hage, J.J. ; Schukken, Y.H. ; Schols, H. ; Maris-Veldhuis, M.A. ; Rijsewijk, F.A.M. ; Klaassen, C.H.L. - \ 2003
Epidemiology and Infection 130 (2003)3. - ISSN 0950-2688 - p. 541 - 552.
rhinotracheitis virus - infectious-diseases - marker vaccine - risk-factors - dairy farms - calves - immunity - type-1 - reactivation - immunization
Transmission of bovine herpesvirus 1 (BHV1) within and between herds was studied on the island of Ameland, The Netherlands. There were 50 herds with 3300 head of cattle on the island. Herds were divided into three groups: (1) only containing seronegative cattle, (2) containing seronegative cattle and vaccinated seropositive cattle, and (3) containing only vaccinated cattle. All 23 herds in groups 1 and 2 were monitored. Three major outbreaks of BHV1 infections were observed due to the introduction of infectious cattle. Another major outbreak was most likely induced by reactivation of latent BHV1 in seropositive cattle. The basic reproduction ratio within these herds was estimated at least 4. Only one of these outbreaks led to three secondary outbreaks in susceptible herds in which all cattle were seronegative. These outbreaks were most likely due to respectively, direct animal contact, human transmission, and aerogenic transmission. The basic reproduction ratio between herds in this study was estimated to be 0(.)6.
Quantification of the effect of control strategies on classical swine fever epidemics
Klinkenberg, D. ; Everts-van der Wind, A. ; Graat, E.A.M. ; Jong, M.C.M. de - \ 2003
Mathematical Biosciences 186 (2003)2. - ISSN 0025-5564 - p. 145 - 173.
subunit vaccine - marker vaccine - virus - transmission
Emergency vaccination during an epidemic of classical swine fever virus (CSFV) has become a serious option because of the ethical problems of strategies with massive culling and the availability of a marker vaccine that reduces virus transmission. Here we present a model of between-herd CSFV transmission, which quantifies the effect of control strategies with and without vaccination. We estimate the model parameters from data of the Dutch CSFV epidemic of 1997/1998. With the model, a set of control strategies is compared, consisting of five control measures in several combinations. Consequently, the following general requirements of successful strategies can be formulated. First, to achieve extinction of a CSFV epidemic, transmission through transport should be prevented and the indirect virus transmission, i.e. all transmission not through animal contacts, should at least be halved, either by vaccination or by culling of the susceptible pig population. Second, to minimize the size and duration of an epidemic, the extinction requirements should be met quickly and indirect virus transmission should be reduced by far more than a half. Although the origin of the model parameters let the requirements in fact be only applicable for the south-eastern part of the Netherlands, it is argued that epidemics in other areas will not need stricter control strategies. (C) 2003 Elsevier Inc. All rights reserved.
Influence of maternal antibodies on efficacy of a subunit vaccine: transmission of classical swine fever virus between pigs vaccinated at 2 weeks of age
Klinkenberg, D. ; Moormann, R.J.M. ; Smit, A.J. de; Bouma, A. ; Jong, M.C.M. de - \ 2002
Vaccine 20 (2002)23-24. - ISSN 0264-410X - p. 3005 - 3013.
marker vaccine - pseudorabies virus - 1997-1998 epidemic - pregnant sows - e2 - netherlands - immunity - protection - strategies - disease
This study shows the effectiveness of vaccination with an E2 subunit vaccine against classical swine fever (CSF) in 2-week-old piglets. Half of the piglets were carrying maternally derived antibodies (MDAs) at the time of vaccination. Three and 6 months later, antibody levels were compared between the two treatments. Moreover, reduction of virus transmission was investigated at 3 and 6 months by doing transmission experiments. The vaccine was found to be capable of reducing virus transmission significantly at both time intervals. Maternal immunity reduced vaccination-induced antibody levels after 3 and 6 months and possibly led to a less effective protection against virus transmission after 6 months.
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