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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Een analyse van mogelijke aanpassingen van de dode wilde vogelsurveillance voor de vroegtijdige opsporing van introducties van vogelgriepvirus
Gonzales, J.L. ; Germeraad, Eveline A. ; Rijks, J.M. ; Petie, R. ; Beerens, N. ; Stahl, J. ; Slaterus, R. ; Elbers, A.R.W. - \ 2019
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.
Rate of introduction of a low pathogenic avian influenza virus infection in different poultry production sectors in the Netherlands
Gonzales, J.L. ; Stegeman, J.A. ; Koch, G. ; Wit, S.J. de; Elbers, A.R.W. - \ 2013
Influenza and Other Respiratory Viruses 7 (2013)1. - ISSN 1750-2640 - p. 6 - 10.
turkeys - risk
Background Targeted risk-based surveillance of poultry types (PT) with different risks of introduction of low pathogenic avian influenza virus (LPAIv) infection may improve the sensitivity of surveillance. Objective To quantify the rate of introduction of LPAIv infections in different PT. Methods Data from the Dutch LPAIv surveillance programme (2007–2010) were analysed using a generalised linear mixed and spatial model. Results Outdoor-layer, turkey, duck-breeder and meat-duck, farms had a 11, 8, 24 and 13 times higher rate of introduction of LPAIv than indoor-layer farms, respectively. Conclusion Differences in the rate of introduction of LPAIv could be used to (re)design a targeted risk-based surveillance programme.
A sero-surveillance programme for early detection of LPAIv outbreaks in layer chickens
Gonzales, J.L. ; Boender, G.J. ; Stegeman, J.A. ; Elbers, A.R.W. ; Koeijer, A.A. de - \ 2012
Transmission characteristics of low pathogenic avian influenza virus of H7N7 and H5N7 subtypes in layer chickens
Gonzales, J.L. ; Elbers, A.R.W. ; Bouma, A. ; Koch, G. ; Wit, J.J. de; Stegeman, J.A. - \ 2012
Veterinary Microbiology 155 (2012)2-4. - ISSN 0378-1135 - p. 207 - 213.
quantification - infection - vaccine - epidemiology - poultry
Lowpathogenicavianinfluenzavirus (LPAIv) infections of H5 and H7 subtypes in poultry are notifiable to the OIE, hence surveillance programmes are implemented. The rate at which LPAIv strains spread within a flock determines the prevalence of infected birds and the time it takes to reach that prevalence and, consequently, optimal sample size and sampling frequency. The aim of this study was to investigate the transmissioncharacteristics of an H7N7 and an H5N7 LPAIv in layerchickens. Two transmission experiments were performed, which consisted of 30 (first experiment) and 20 (second experiment) pairs of conventional layers, respectively. At the start of the experiments, one chicken per pair was inoculated with LPAIv and the other chicken was contact-exposed. Occurrence of infection was monitored by regularly collecting tracheal and cloacal swab samples, which were examined for the presence of virus RNA by RT-PCR. The results of the test were used to estimate the transmission rate parameter (ß), the infectious period (T) and the basic reproduction ratio (R0). In addition, egg production and virus shedding patterns were quantified. For the H7N7virus, the ß, T and R0 estimates were 0.10 (95% confidence interval (CI): 0.04–0.18) day-1, 7.1 (95% CI: 6.5–7.8) days and 0.7 (95% CI: 0.0–1.7), respectively. With the H5N7virus, only a few inoculated chickens (5 out of 20) became infected and no transmission was observed. This study shows that transmissioncharacteristics of LPAIv strains may vary considerably, which has to be taken into account when designing surveillance programmes.
Using egg production data to quantify within-flock transmission of low pathogenic avian influenza virus in commercial layer chickens
Gonzales, J.L. ; Elbers, A.R.W. ; Goot, J.A. van der; Bontje, D.M. ; Koch, G. ; Wit, J.J. de; Stegeman, J.A. - \ 2012
Preventive Veterinary Medicine 107 (2012)3-4. - ISSN 0167-5877 - p. 253 - 259.
southern china - epidemiology - netherlands - h7n7 - quantification - vaccination - population - evolution - infection - outbreak
Even though low pathogenic avian influenza viruses (LPAIv) affect the poultry industry of several countries in the world, information about their transmission characteristics in poultry is sparse. Outbreak reports of LPAIv in layer chickens have described drops in egg production that appear to be correlated with the virus transmission dynamics. The objective of this study was to use egg production data from LPAIv infected layer flocks to quantify the within-flock transmission parameters of the virus. Egg production data from two commercial layer chicken flocks which were infected with an H7N3 LPAIv were used for this study. In addition, an isolate of the H7N3 LPAIv causing these outbreaks was used in a transmission experiment. The field and experimental estimates showed that this is a virus with high transmission characteristics. Furthermore, with the field method, the day of introduction of the virus into the flock was estimated. The method here presented uses compartmental models that assume homogeneous mixing. This method is, therefore, best suited to study transmission in commercial flocks with a litter (floor-reared) housing system. It would also perform better, when used to study transmission retrospectively, after the outbreak has finished and there is egg production data from recovered chickens. This method cannot be used when a flock was affected with a LPAIv with low transmission characteristics (R0 <2), since the drop in egg production would be low and likely to be confounded with the expected decrease in production due to aging of the flock. Because only two flocks were used for this analysis, this study is a preliminary basis for a proof of principle that transmission parameters of LPAIv infections in layer chicken flocks could be quantified using the egg production data from affected flocks.
Cost Analysis of Various Low Pathogenic Avian Influenza Surveillance Systems in the Dutch Egg Layer Sector
Rutten, N. ; Gonzales, J.L. ; Elbers, A.R. ; Velthuis, A.G.J. - \ 2012
PLoS ONE 7 (2012)4. - ISSN 1932-6203 - 9 p.
poultry - risk - viruses - epidemiology - netherlands - validation - chickens
Background As low pathogenic avian influenza viruses can mutate into high pathogenic viruses the Dutch poultry sector implemented a surveillance system for low pathogenic avian influenza (LPAI) based on blood samples. It has been suggested that egg yolk samples could be sampled instead of blood samples to survey egg layer farms. To support future decision making about AI surveillance economic criteria are important. Therefore a cost analysis is performed on systems that use either blood or eggs as sampled material. Methodology/Principal Findings The effectiveness of surveillance using egg or blood samples was evaluated using scenario tree models. Then an economic model was developed that calculates the total costs for eight surveillance systems that have equal effectiveness. The model considers costs for sampling, sample preparation, sample transport, testing, communication of test results and for the confirmation test on false positive results. The surveillance systems varied in sampled material (eggs or blood), sampling location (farm or packing station) and location of sample preparation (laboratory or packing station). It is shown that a hypothetical system in which eggs are sampled at the packing station and samples prepared in a laboratory had the lowest total costs (i.e. € 273,393) a year. Compared to this a hypothetical system in which eggs are sampled at the farm and samples prepared at a laboratory, and the currently implemented system in which blood is sampled at the farm and samples prepared at a laboratory have 6% and 39% higher costs respectively. Conclusions/Significance This study shows that surveillance for avian influenza on egg yolk samples can be done at lower costs than surveillance based on blood samples. The model can be used in future comparison of surveillance systems for different pathogens and hazards
Transmission between chickens of an H7N1 low pathogenic avian influenza virus isolated during the epidemic of 1999 in Italy.
Gonzales, J.L. ; Goot, J.A. van der; Stegeman, J.A. ; Elbers, A.R.W. ; Koch, G. - \ 2011
Veterinary Microbiology 152 (2011)1-2. - ISSN 0378-1135 - p. 187 - 190.
hemagglutinin - emergence - h5n2
The transmissibility of an H7N1 Low Pathogenic Avian Influenza (LPAI) virus isolated from a turkey flock during the large epidemic in Italy in 1999, was experimentally studied in chickens. Four group transmission experiments were performed. Infection and transmission were monitored by means of virus isolation on swab samples and antibody detection in serum samples. From the results of these groups, we estimated the mean infectious period at 7.7 (6.7–8.7) days, the transmission rate parameter at 0.49 (0.30–0.75) infections per infectious chicken per day and the basic reproduction ratio at 3.8 (1.3–6.3). These estimates can be used for the development of surveillance and control programmes of LPAI in poultry.
Low-pathogenic notifiable avian influenza serosurveillance and the risk of infection in poultry - a critical review of the European Union active surveillance programme (2005-2007)
Gonzales, J.L. ; Elbers, A.R.W. ; Bouma, A. ; Koch, G. ; Wit, J.J. de; Stegeman, J.A. - \ 2010
Influenza and Other Respiratory Viruses 4 (2010)2. - ISSN 1750-2640 - p. 91 - 99.
h7n7 epidemic - virus h7n7 - netherlands - outbreaks - performance - farms
Background Since 2003, Member States (MS) of the European Union (EU) have implemented serosurveillance programmes for low pathogenic notifiable avian influenza (LPNAI) in poultry. To date, there is the need to evaluate the surveillance activity in order to optimize the programme's surveillance design. Objectives To evaluate MS sampling operations [sample size and targeted poultry types (PTs)] and its relation with the probability of detection and to estimate the PTs relative risk (RR) of being infected. Methods Reported data of the surveillance carried out from 2005 to 2007 were analyzed using: (i) descriptive indicators to characterize both MS sampling operations and its relation with the probability of detection and the LPNAI epidemiological situation, and (ii) multivariable methods to estimate each PTs RR of being infected. Results Member States sampling a higher sample size than that recommended by the EU had a significantly higher probability of detection. Poultry types with ducks & geese, game-birds, ratites and "others" had a significant higher RR of being seropositive than chicken categories. The seroprevalence in duck & geese and game-bird holdings appears to be higher than 5%, which is the EU-recommended design prevalence (DP), while in chicken and turkey categories the seroprevalence was considerably lower than 5% and with that there is the risk of missing LPNAI seropositive holdings. Conclusion It is recommended that the European Commission discusses with its MS whether the results of our evaluation calls for refinement of the surveillance characteristics such as sampling frequency, the between-holding DP and MS sampling operation strategies.
Sensitivity of the European Union low pathogenic avian influenza serological surveillance program.
Gonzales, J.L. ; Elbers, A.R.W. ; Bouma, A. ; Stegeman, J.A. - \ 2009
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