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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    Transmission of African Swine Fever Virus via carrier (survivor) pigs does occur
    Eblé, P.L. ; Hagenaars, T.J. ; Weesendorp, E. ; Quak, S. ; Moonen-Leusen, H.W. ; Loeffen, W.L.A. - \ 2019
    Veterinary Microbiology 237 (2019). - ISSN 0378-1135
    African Swine Fever - Carrier - Environment - Reproduction ratio - Survivor - Transmission

    We investigated whether ASF carrier pigs that had completely recovered from an acute infection with ASFV Netherlands ‘86, could transmit the disease to naive pigs by direct contact transmission. For this, we used pigs that had survived an ASFV infection, had recovered from disease, and had become carriers of ASFV. These clinically healthy carriers were put together one-by-one with naive contact pigs. Two of the twelve contact pigs developed an acute ASFV infection. Using the results of the experiment we quantified the transmission parameters βcarrier (0.039/day) and Tcarrier (25.4 days). With the survival rate of 0.3 for our ASFV isolate, these parameter values translate into the contribution of carriers to R0 in groups of pigs being 0.3. Further, we placed naive contact pigs in an ASFV contaminated environment. Here, no contact infections were observed. Our findings show that clinically healthy carriers can be a source of acute new infections, which can contribute to the persistence of ASFV in swine populations. The estimates that we provide can be used for modelling of transmission in domestic pigs and, in part, for modelling transmission in wild boar.

    Efficacy of CSF vaccine CP7_E2alf in piglets with maternally derived antibodies
    Eble, P.L. ; Quak, S. ; Geurts, Y. ; Moonen-Leusen, H.W.M. ; Loeffen, W.L.A. - \ 2014
    Veterinary Microbiology 174 (2014)1-2. - ISSN 0378-1135 - p. 27 - 38.
    There is a need for live DIVA (differentiating infected from vaccinated animals) vaccines against classical swine fever (CSF). The aim of this study was to investigate whether vaccination with the chimeric pestivirus vaccine CP7_E2alf is efficacious to protect young piglets born from vaccinated sows, thus with maternally derived antibodies (MDAs). Groups of 10 piglets each, with or without MDAs, were vaccinated either intramuscularly (IM), at an age of 3 or 6 weeks, or orally (OR), at an age of 6 weeks. Five piglets of each group were challenged with CSFV strain Koslov and protection against clinical disease, virus shedding and transmission were studied. Vaccination with CP7_E2alf, both in the presence of MDA's and in piglets without MDA's, protected against severe clinical signs, but virus shedding from most inoculated piglets and transmission to contact pigs was observed. However, virus transmission in the vaccinated piglets was significantly reduced as compared to non-vaccinated piglets, although the reproduction ratio's R calculated from the results in the vaccinated pigs from our study were not yet significantly below 1. The efficacy of vaccination with CP7_E2alf in the presence of MDAs (RIMvac = 0.8, RORvac = 0.4) seemed to be slightly less as compared to vaccination in the absence of MDAs (RIMvac = 0.2, RORvac = 0). On a population level, the results suggest that the CP7_E2alf vaccine is an effective tool in the control and eradication of CSF and, moreover, can be applied for both IM and oral use for young age groups, with MDAs having a limited effect on the efficacy.
    Suitability of faeces and tissue samples as a basis for non-invasive sampling for African swine fever in wild boar
    Carvalho Ferreira, H.C. de; Weesendorp, E. ; Quak, S. ; Stegeman, J.A. ; Loeffen, W.L.A. - \ 2014
    Veterinary Microbiology 172 (2014)3-4. - ISSN 0378-1135 - p. 449 - 454.
    terrestrial ecosystems - sus-scrofa - virus - size - europe - pigs
    A challenging aspect of ASFV control in wild boar populations is the design and implementation of effective surveillance and monitoring programmes, both for early warning, and to determine the ongoing epidemiological situation in an infected population. Testing blood samples requires invasive sampling strategies like hunting or capture of wild boar. Besides being biased towards healthy animals, such strategies are also linked to further spread of the virus. Non-invasive sampling strategies would increase the reliability of surveillance of ASFV in wild boar populations, without the negative side effects. This study evaluates the potential of faeces and tissue samples as a basis for non-invasive sampling strategies for ASFV in wild boar. In the acute phase (0–21 days after infection), in comparison with virus detection in blood, virus can be detected in faeces 50–80% of the time. This percentage decreases to below 10% for the subacute/chronic phase. ASFV DNA is quite stable in faeces. Half-lives range from more than 2 years at temperature up to 12 °C, to roughly 15 days at temperatures of 30 °C. In tissue samples, stored at 20 °C, half-lives mostly range from 1.7 to 7.4 days. The sample of preference is the spleen, where the highest titres and highest half-life of ASFV DNA are observed. The level and duration of excretion of ASFV in the faeces, combined with the stability of the DNA, suggest that sampling of faeces could be the basis for a non-invasive sampling strategy to monitor ASFV in wild boar.
    Herberekening Streefbeeld Aal: Een analyse van het bestaande Nederlandse streefbeeld in relatie tot de buurlanden. Een advies op verzoek van de minister van Economische Zaken
    Rabbinge, R. ; Meer, J. van der; Quak, J. ; Verreth, J.A.J. ; Waal, A. van der; Nagelkerke, L.A.J. - \ 2013
    www.rijksoverheid.nl - 87
    european eels - populatiedichtheid - monitoring - vismigratie - referentienormen - inventarisaties - nederland - population density - fish migration - reference standards - inventories - netherlands
    Vanuit de Tweede Kamer is gesteld dat het streefbeeld voor uittrek van schieraal te hoog is. In het huidige Nederlandse streefbeeld is te weinig rekening is gehouden met factoren als veranderende voedselrijkdom van de Nederlandse wateren, het uitzetten van glas- en pootaal en de aanleg van migratiebeperkende kunstwerken zoals sluizen en gemalen. In dat kader is ingesteld de commissie ‘Herberekening streefbeeld paling’ o.l.v. Prof. Dr. Rabbinge. De resultaten worden in dit rapport gegeven
    Quantification of airborne African Swine Fever virus after experimental infection
    Carvalho Ferreira, H.C. de; Weesendorp, E. ; Quak, S. ; Stegeman, J.A. ; Loeffen, W.L.A. - \ 2013
    Veterinary Microbiology 165 (2013)3-4. - ISSN 0378-1135 - p. 243 - 251.
    mouth-disease virus - enterococcus-faecalis - aerosol transmission - pigs - spread
    Knowledge on African Swine Fever (ASF) transmission routes can be useful when designing control measures against the spread of ASF virus (ASFV). Few studies have focused on the airborne transmission route, and until now no data has been available on quantities of ASF virus (ASFV) in the air. Our aim was to validate an air sampling technique for ASF virus (ASFV) that could be used to detect and quantify virus excreted in the air after experimental infection of pigs. In an animal experiment with the Brazil'78, the Malta'78 and Netherlands'86 isolates, air samples were collected at several time points. For validation of the air sampling technique, ASFV was aerosolised in an isolator, and air samples were obtained using the MD8 air scan device, which was shown to be suitable to detect ASFV. The half-life of ASFV in the air was on average 19 min when analysed by PCR, and on average 14 min when analysed by virus titration. In rooms with infected pigs, viral DNA with titres up to 10(3.2) median tissue culture infective dose equivalents (TCID50eq.)/m(3) could be detected in air samples from day 4 post-inoculation (dpi 4) until the end of the experiments, at dpi 70. In conclusion, this study shows that pigs infected with ASFV will excrete virus in the air, particularly during acute disease. This study provides the first available parameters to model airborne transmission of ASFV.
    Efficacy of chimeric Pestivirus vaccine candidates against Classical Swine Fever: protection and DIVA characteristics
    Eble, P.L. ; Geurts, Y. ; Quak, J. ; Moonen-Leusen, H.W.M. ; Blome, S. ; Hofmann, M.A. ; Koenen, F. ; Beer, M. ; Loeffen, W.L.A. - \ 2013
    Veterinary Microbiology 162 (2013)2-4. - ISSN 0378-1135 - p. 437 - 446.
    subunit marker vaccine - hog-cholera virus - monoclonal-antibodies - pigs - transmission - differentiation - strains - infection - virulent - induce
    Currently no live DIVA (Differentiating Infected from Vaccinated Animals) vaccines against classical swine fever (CSF) are available. The aim of this study was to investigate whether chimeric pestivirus vaccine candidates (CP7_E2alf, Flc11 and Flc9) are able to protect pigs against clinical signs, and to reduce virus shedding and virus transmission, after a challenge with CSF virus (CSFV), 7 or 14 days after a single intramuscular vaccination. In these vaccine candidates, either the E2 or the Erns encoding genome region of a bovine viral diarrhoea virus strain were combined with a cDNA copy of CSFV or vice versa. Furthermore, currently available serological DIVA tests were evaluated. The vaccine candidates were compared to the C-strain. All vaccine candidates protected against clinical signs. No transmission to contact pigs was detected in the groups vaccinated with C-strain, CP7_E2alf and Flc11. Limited transmission occurred in the groups vaccinated with Flc9. All vaccine candidates would be suitable to stop on-going transmission of CSFV. For Flc11, no reliable differentiation was possible with the current Erns-based DIVA test. For CP7_E2alf, the distribution of the inhibition percentages was such that up to 5% false positive results may be obtained in a large vaccinated population. For Flc9 vaccinated pigs, the E2 ELISA performed very well, with an expected 0.04% false positive results in a large vaccinated population. Both CP7_E2alf and Flc9 are promising candidates to be used as live attenuated marker vaccines against CSF, with protection the best feature of CP7_E2alf, and the DIVA principle the best feature of Flc9.
    Zicht op vangsten recreatieve visserij : een nieuwe methode en eerste resultaten
    Graaf, M. de; Quak, J. - \ 2012
    Visserijnieuws 32 (2012)19. - ISSN 1380-5061 - p. 4 - 4.
    sportvissen - sportzeevisserij - visvangsten - kabeljauw - palingen - visserij - game fishes - sea fishing - fish catches - cod - eels - fisheries
    Recreatieve vissers hebben in 2010 naar schatting 382 ton kabeljauw gevangen en daarvan 23 ton teruggezet. Die vangst is ruim tien procent van de commerciele vangst van 3.219 ton door de beroepsvissersvloot dat jaar. De gezamenlijke aalvangst door recreatieve vissers op zee en in binnenwater in 2010 wordt geschat op 231 ton, ondanks een terugzetverplichting voor de meeste wateren werd 55 ton meegenomen. De commerciele vangst dat jaar was naar schatting 442 ton. Zo blijkt iot het IMARES-rapport 'Recreational fishery in the Netherlands in 2010' van de auteurs Tessa van der Hamen en Martin de Graaf.
    Seroprevalence of antibodies to Schmallenberg virus in dairy cattle, winter 2011-2012
    Elbers, A.R.W. ; Loeffen, W.L.A. ; Quak, J. ; Boer-Luijtze, E.A. de; Spek, N.A. van der; Bouwstra, R.J. ; Maas, R. van der; Spierenburg, A.M. ; Kluijver, P.E. ; Schaik, G. van; Poel, W.H.M. van der - \ 2012
    Open data and beyond: Exploring existing open data projects to prepare a successful open data strategy
    Loenen, B. van; Bregt, A.K. ; Bruinenberg, J. ; Castelein, W. ; Doorn, L. van; Juffermans, P. ; Kulk, S. ; Mourik, D. van; Oosterom, P. van; Ploeger, H. ; Quak, W. ; Vries, M. de; Zweistra, M. - \ 2012
    Delft : OTB - 212 p.
    African swine fever virus excretion patterns in persistently infected animals: A quantitative approach
    Carvalho Ferreira, H.C. de; Weesendorp, E. ; Elbers, A.R.W. ; Bouma, A. ; Quak, S. ; Stegeman, J.A. ; Loeffen, W.L.A. - \ 2012
    Veterinary Microbiology 160 (2012)3-4. - ISSN 0378-1135 - p. 327 - 340.
    western hemisphere - pigs - virulence
    The continuing circulation of African swine fever (ASF) in Russia and in the Trans-Caucasian countries has led to increased efforts in characterizing the epidemiology of ASF. For a better insight in epidemiology, quantitative data on virus excretion is required. Until now, excretion data has mainly focused on the initial stages of the disease. In our study we have studied ASF virus (ASFV) excretion dynamics in persistently infected animals. For this purpose, virus excretion through different routes was quantified over 70 days after infection. Three virus isolates of moderate virulence were used: the Brazil’78, the Malta’78 (a low and a high inoculation dose) and the Netherlands’86 isolate. For each isolate or dose, 10 animals were used. All (Brazil’78 group), or three animals per group were inoculated and the other animals served as contact animals. It was shown that dose (Malta’78 low or high) or infection route (inoculated or naturally infected) did not influence the ASFV excretion (p > 0.05). Nasal, ocular and vaginal excretions showed the lowest ASFV titres. Virus was consistently present in the oropharyngeal swabs, showing two peaks, for up to 70 days. Virus was occasionally present in the faeces, occasionally with very high titres. Viral DNA persisted in blood for up to 70 days. The results presented in this study show that a high proportion of persistently infected animals shed virus into the environment for at least 70 days, representing a possible risk for transmission and that should be considered in future epidemiological analysis of ASF.
    Development of a virus neutralisation test to detect antibodies against Schmallenberg virus and serological results in suspect and infected herds
    Loeffen, W.L.A. ; Quak, J. ; Boer-Luijtze, E.A. de; Hulst, M.M. ; Poel, W.H.M. van der; Bouwstra, R.J. ; Maas, H.A. - \ 2012
    Acta Veterinaria Scandinavica 54 (2012). - ISSN 0044-605X
    akabane virus - orthobunyavirus - shamonda - nigeria - cattle - japan
    Background: At the end of 2011, a new orthobunyavirus, tentatively named Schmallenberg virus (SBV), was discovered in Germany. This virus has since been associated with clinical signs of decreased milk production, watery diarrhoea and fever in dairy cows, and subsequently also with congenital malformations in calves, lambs and goat kids. In affected countries, initial surveillance for the infection was based on examination of malformed progeny. These suspicions were followed up by real-time reverse transcription polymerase chain reaction (RT-PCR) on brain tissue. For epidemiological purposes, a serological assay was, however, needed. Results: A virus neutralisation test (VNT) was developed and optimized, and subsequently evaluated. This VNT has a specificity of >99% and the sensitivity is likely also very close to 100%. The assay is highly repeatable and reproducible. The final assay was used to test for antibodies in cows, ewes and does from herds known to be infected or suspected to be so. Targets for sampling in these herds were the mothers of malformed offspring. In herds with an RT-PCR confirmed SBV infection, more than 94% (190 out of 201) of the ewes and 99% (145 out of 146) of the cows were seropositive. In herds with suspicion of SBV infection based on birth of malformed offspring only (no or negative RT-PCR), more than 90% (231 out of 255) of the ewes and 95% (795 out of 834) of the cows were seropositive. In goats, on the other hand, only a low number of seropositives was found: overall 36.4%, being 16 out of 44 goats tested. Conclusions: Given the characteristics of this VNT, it can be used at a relative high throughput for testing of animals for export, surveillance, screening and research purposes, but can also be used as a confirmation test for commercially available enzyme-linked immunosorbent assays (ELISA's) and for (relative) quantification of antibodies. Suspicions of SBV infections that were confirmed by RT-PCR were almost always confirmed by serology in cows. Due to individual registration and identification of cows and calves, affected offspring could almost always be traced back to the mother. Ewes on the other hand were not always the mothers of affected lambs, but were in many cases herd mates with unaffected lambs. This indicated a high within-herd seroprevalence of antibodies against SBV.
    Seroprevalence of Schmallenberg Virus Antibodies among Dairy Cattle, the Netherlands, Winter 2011-2012
    Elbers, A.R. ; Loeffen, W.L.A. ; Quak, J. ; Boer-Luijtze, E.A. de; Spek, A.N. van der; Bouwstra, R.J. ; Maas, H.A. ; Spierenburg, M.A.H. ; Kluijver, E.P. de; Schaik, G. van; Poel, W.H.M. van der - \ 2012
    Emerging Infectious Diseases 18 (2012)7. - ISSN 1080-6040 - p. 1065 - 1071.
    akabane virus - orthobunyavirus - arthrogryposis - infections - australia - shamonda - nigeria - japan
    Infections with Schmallenberg virus (SBV) are associated with congenital malformations in ruminants. Because reporting of suspected cases only could underestimate the true rate of infection, we conducted a seroprevalence study in the Netherlands to detect past exposure to SBV among dairy cattle. A total of 1,123 serum samples collected from cattle during November 2011–January 2012 were tested for antibodies against SBV by using a virus neutralization test; seroprevalence was 72.5%. Seroprevalence was significantly higher in the central-eastern part of the Netherlands than in the northern and southern regions (p
    Efficacy of a pandemic (H1N1) 2009 virus vaccine in pigs against the pandemic influenza virus is superior to commercially available swine influenza vaccines.
    Loeffen, W.L.A. ; Stockhofe-Zurwieden, N. ; Weesendorp, E. ; Zoelen-Bos, D.J. van; Heutink, R. ; Quak, J. ; Goovaerts, D. ; Heldens, J. ; Maas, H.A. ; Moormann, R.J.M. ; Koch, G. - \ 2011
    Veterinary Microbiology 152 (2011)3-4. - ISSN 0378-1135 - p. 304 - 314.
    fever virus - new-jersey - fort-dix - a-virus - transmission - pathogenesis - isolations - infection - quantification - outbreak
    In April 2009 a new influenza A/H1N1 strain, currently named “pandemic (H1N1) influenza 2009¿ (H1N1v), started the first official pandemic in humans since 1968. Several incursions of this virus in pig herds have also been reported from all over the world. Vaccination of pigs may be an option to reduce exposure of human contacts with infected pigs, thereby preventing cross-species transfer, but also to protect pigs themselves, should this virus cause damage in the pig population. Three swine influenza vaccines, two of them commercially available and one experimental, were therefore tested and compared for their efficacy against an H1N1v challenge. One of the commercial vaccines is based on an American classical H1N1 influenza strain, the other is based on a European avian H1N1 influenza strain. The experimental vaccine is based on reassortant virus NYMC X179A (containing the hemagglutinin (HA) and neuraminidase (NA) genes of A/California/7/2009 (H1N1v) and the internal genes of A/Puerto Rico/8/34 (H1N1)). Excretion of infectious virus was reduced by 0.5–3 log10 by the commercial vaccines, depending on vaccine and sample type. Both vaccines were able to reduce virus replication especially in the lower respiratory tract, with less pathological lesions in vaccinated and subsequently challenged pigs than in unvaccinated controls. In pigs vaccinated with the experimental vaccine, excretion levels of infectious virus in nasal and oropharyngeal swabs, were at or below 1 log10 TCID50 per swab and lasted for only 1 or 2 days. An inactivated vaccine containing the HA and NA of an H1N1v is ably to protect pigs from an infection with H1N1v, whereas swine influenza vaccines that are currently available are of limited efficaciousness. Whether vaccination of pigs against H1N1v will become opportune remains to be seen and will depend on future evolution of this strain in the pig population. Close monitoring of the pig population, focussing on presence and evolution of influenza strains on a cross-border level would therefore be advisable.
    Population dynamics of swine influenza virus in farrow-to-finish and specialised finishing herds in the Netherlands
    Loeffen, W.L.A. ; Hunneman, W.A. ; Quak, J. ; Verheijden, J.H.M. ; Stegeman, J.A. - \ 2009
    Veterinary Microbiology 137 (2009)1-2. - ISSN 0378-1135 - p. 45 - 50.
    aujeszkys-disease virus - a-viruses - respiratory-disease - fattening pigs - european pigs - great-britain - h1n2 - porcine - infections - prevalence
    Influenza virus infections with subtypes H1N1, H3N2 and H1N2 are very common in domestic pigs in Europe. Data on possible differences of population dynamics in finishing pigs in farrow-to-finish herds and in specialised finishing herds are, however, scarce. The presence of sows and weaned piglets on the same premises may, however, affect the exposure of finishing pigs to influenza viruses. In a longitudinal study on 14 farrow-to-finish herds and 15 finishing herds, groups of pigs were followed by repeatedly testing the same animals for antibodies against all three influenza virus subtypes (H1N1, H3N2 and H1N2). At the end of the finishing period, the seroprevalences in farrow-to-finish and specialised finishing herds were 44.3% and 62.0%, respectively for H1N1, 6.6% and 19.3%, respectively for H3N2, and 57.2% and 25.6%, respectively for H1N2. For all three subtypes, the incidence of influenza virus infections was highest at the beginning of the finishing period in farrow-to-finish herds, while the incidence of influenza virus infections was highest at the end of the finishing period in finishing herds. Respiratory disease, probably related to the influenza infections, was observed in five of these herds only, but also occurred at the beginning of the finishing period in farrow-to-finish herds and at the end of the finishing period in finishing herds. The observed differences of population dynamics of influenza virus may affect choice and timing of intervention measures
    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
    Limited BVDV transmission and full protection against CSFV transmission in pigs experimentally infected with BVDV type 1b
    Wieringa-Jelsma, H. ; Quak, J. ; Loeffen, W.L.A. - \ 2006
    Veterinary Microbiology 118 (2006)1-2. - ISSN 0378-1135 - p. 26 - 36.
    viral diarrhea virus - classical swine-fever - hog-cholera virus - monoclonal-antibodies - neutralizing antibody - vaccine - signs - epidemiology - inoculation - challenge
    Bovine viral diarrhea virus (BVDV) in pigs may interfere with the detection and epidemiology of classical swine fever virus (CSFV). To investigate the importance of BVDV infections in pigs, first we studied the transmission dynamics of a recent BVDV field isolate. Subsequently, the protection of BVD antibodies against transmission and clinical disease of CSF virus was studied. Only limited transmission of BVDV occurred (R = 0.20), while no CSFV transmission occurred in pigs with BVDV antibodies. We concluded that BVDV transmission among pigs is possible, but seems to be limited and thus the virus should disappear from a population if no new introductions occur. Furthermore, the presence of BVD antibodies may completely prevent the transmission of CSFV and therefore could protect pigs against classical swine fever. It was also noticed that double infections with BVDV and CSFV were incorrectly diagnosed using the neutralization peroxidase linked assay (NPLA), which is the golden standard for antibody detection. This might hamper the diagnosis of CSF in herds with a high BVD prevalence
    A simple, rapid and reliable enzyme-linked immunosorbent assay for the detection of bovine virus diarrhoea virus (BVDV) specific antibodies in cattle serum, plasma and bulk milk
    Kramps, J.A. ; Maanen, C. van; Wetering, G. van de; Stienstra, G. ; Quak, S. ; Brinkhof, J. ; Ronsholt, L. ; Nylin, B. - \ 1999
    Veterinary Microbiology 64 (1999)2-3. - ISSN 0378-1135 - p. 135 - 144.
    To detect Bovine Virus Diarrhoea Virus (BVDV)-specific antibodies in cattle serum, plasma and bulk milk, a simple, reliable and rapid blocking ELISA ("Ceditest") has been developed using two monoclonal antibodies ("WB112" and "WB103") directed to different highly conserved epitopes on the non-structural peptide NS3 of pestiviruses. The test can be performed at high reproducibility using undiluted samples. In testing 1000 field serum samples, the ELISA showed a specificity and a sensitivity relative to the virus neutralization test of 99% and 98%, respectively. The blocking ELISA is able to detect specific antibodies in serum obtained 12 days after an acute infection and in serum of vaccinated and challenged animals. A frequency distribution diagram, obtained by testing almost 1800 random Dutch field serum samples, showed a clear separation between a negative population (maximum frequency of the % inhibition at −5%) and a positive population (maximum frequency of the % inhibition at 95%). Based on these data, the prevalence of seropositive animals was 65% (95% confidence interval: 63%–67%). By exchanging plasma- and bulk milk samples between two laboratories (The Netherlands and Denmark), a good overall agreement was found between results obtained with the Ceditest and those obtained with the Danish blocking ELISA as used in the Danish BVDV eradication programme. The results indicate that BVDV infections can reliably be diagnosed by the Ceditest ELISA and that the test is suitable for use in large scale screening and eradication programmes.
    The promising impact of ley introduction and herd expansion on soil organic matter content in southern Mali
    Bosma, R.H. ; Kanté, S. ; Kébé, D. ; Quak, W. - \ 1999
    Agricultural Systems 62 (1999). - ISSN 0308-521X - p. 1 - 15.
    Activités de production agricole durable
    Quak, W. ; Hengsdijk, H. ; Touré, M.S.M. ; Sissoko, K. ; Camara, O. ; Dembélé, N.F. ; Bakker, E.J. - \ 1998
    In: L'intensification agricole au Sahel / Breman, H., Sissoko, K., Paris : Karthala - p. 539 - 561.
    Résultats de la planification u buts multiples. Niveau unité de production agricole (Koutiala)
    Touré, M.S.M. ; Bakker, E.J. ; Sissoko, K. ; Quak, W. - \ 1998
    In: L'intensification agricole au Sahel / Breman, H., Sissoko, K., Paris : Karthala - p. 671 - 629.
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