Prof. dr. Gerdien van Schaik obtained an MSc in Animal Science at Wageningen University, the Netherlands with specializations in Veterinary Epidemiology and a PhD in Animal Health Economics at the same university. From 2004 to 2021, she headed the Epidemiology group of Royal GD, a contract research organization with a large veterinary diagnostic laboratory. GD runs voluntary disease control programs as well as the national surveillance program. In 2015, she was appointed a part-time chair in Monitoring and Surveillance of Farm Animal Health at the faculty of Veterinary Medicine of Utrecht University. Since 2021, she coordinates the European funded H2020 project called DECIDE and combines this with her position as a senior researcher at GD. Her duo appointment provides her with both solid scientific knowledge and practical experience in animal health surveillance.
Since 2007, mortality associated with a previously unreported haemorrhagic disease has been obser... more Since 2007, mortality associated with a previously unreported haemorrhagic disease has been observed in young calves in several European countries. The syndrome, which has been named 'bovine neonatal pancytopenia' (BNP), is characterised by thrombocytopenia, leukocytopenia and a panmyelophthisis. A herd-level case-control study was conducted in four BNP affected countries (Belgium, France, Germany and the Netherlands) to identify herd management risk factors for BNP occurrence. Data were collected using structured face-to-face and telephone interviews of farm managers and their local veterinarians. In total, 363 case farms and 887 control farms were included in a matched multivariable conditional logistic regression analysis. Case-control status was strongly associated with the odds of herd level use of the vaccine PregSure® BVD (PregSure, Pfizer Animal Health) (matched adjusted odds ratio (OR) 107.2; 95% CI: 41.0-280.1). This was also the case for the practices of feeding c...
Ignoring the limited precision of diagnostic tests can incur serious bias in prevalence (P) estim... more Ignoring the limited precision of diagnostic tests can incur serious bias in prevalence (P) estimation. Most studies treat the sensitivity (SE) and specificity (SP) of the tests as constants. This will result in an underestimation of the variability of P. Bayesian inference provides a natural framework with which to integrate the variability in the estimates of SE and SP with estimation of P.1
In the Netherlands, the feasibility of a national control program for infectious bovine rhinotrac... more In the Netherlands, the feasibility of a national control program for infectious bovine rhinotracheitis (IBR) is discussed. The aim of this program would be to achieve freedom from BoHV1 circulation (the causal agent of IBR), in the Dutch cattle population. When IBR would be eradicated, maintaining the free status is essential and insight in the probability of introduction of IBR through cattle imports is crucial. Values for input parameters such as the number of imports per country of origin, herd level prevalence and probability that a random imported animal per age category was either acutely or latently infected with IBR were quantified. A stochastic simulation model was built to predict the basic risk and the efficacy of four risk mitigating scenarios were evaluated. These scenarios involved testing prior to import, import restrictions and vaccination. The model output predicted that IBR infected animals are imported regularly. In an IBR free situation, 571 (5th and 95th percen...
Porcine epidemic diarrhea virus (PEDV) is the highly contagious, causative agent of an economical... more Porcine epidemic diarrhea virus (PEDV) is the highly contagious, causative agent of an economically important acute enteric disease in pigs of all ages. The disease is characterized by diarrhea and dehydration causing mortality and growth retardation. In the last few decades, only classical PEDV was reported sporadically in Europe, but in 2014 outbreaks of PEDV were described in Germany. Phylogenetic analysis showed a very high nucleotide similarity with a variant of PEDV that was isolated in the US in January 2014. The epidemiological situation of PEDV infections in the Netherlands in 2014 was unknown and a seroprevalence study in swine was performed. In total, 838 blood samples from sows from 267 farms and 101 samples from wild boars were collected from May till November 2014 and tested for antibodies against PEDV by ELISA. The apparent herd prevalence of 0.75% suggests that PEDV was not circulating on a large scale in the Netherlands at this time. However, in November 2014 a clin...
Animal health surveillance enables the detection and control of animal diseases including zoonose... more Animal health surveillance enables the detection and control of animal diseases including zoonoses. Under the EU-FP7 project RISKSUR, a survey was conducted in 11 EU Member States and Switzerland to describe active surveillance components in 2011 managed by the public or private sector and identify gaps and opportunities. Information was collected about hazard, target population, geographical focus, legal obligation, management, surveillance design, risk-based sampling, and multi-hazard surveillance. Two countries were excluded due to incompleteness of data. Most of the 664 components targeted cattle (26·7%), pigs (17·5%) or poultry (16·0%). The most common surveillance objectives were demonstrating freedom from disease (43·8%) and case detection (26·8%). Over half of components applied risk-based sampling (57·1%), but mainly focused on a single population stratum (targeted risk-based) rather than differentiating between risk levels of different strata (stratified risk-based). About...
Animal-based welfare assessment is time consuming and expensive. A promising strategy for improvi... more Animal-based welfare assessment is time consuming and expensive. A promising strategy for improving the efficiency of identifying dairy herds with poorer welfare is to first estimate levels of welfare in herds based on data that are more easily obtained. Our aims were to evaluate the potential of herd housing and management data for estimating the level of welfare in dairy herds, and to estimate the associated reduction in the number of farm visits required for identification of herds with poorer welfare in a population. Seven trained observers collected data on 6 animal-based welfare indicators in a selected sample of 181 loose-housed Dutch dairy herds (herd size: 22 to 211 cows). Severely lame cows, cows with lesions or swellings, cows with a dirty hindquarter, and very lean cows were counted, and avoidance distance was assessed for a sample of cows. Occurrence of displacements (social behavior) was recorded in the whole barn during 120 min of observation. For the same herds, data...
The aim of this study was to evaluate whether it was possible to (1) estimate the clinical mastit... more The aim of this study was to evaluate whether it was possible to (1) estimate the clinical mastitis incidence rate (CMI) for all Dutch dairy herds and (2) to detect farms with a high CMI based on routinely collected herd data. For this study, 240 dairy farms with a conventional milking system that participated in the milk recording program every 4 to 6 wk were randomly selected and agreed to participate. From the initial 240 herds, data of clinical mastitis (CM) registrations and routinely collected herd data of 227 herds were complete and could be used for analysis. Routinely collected herd data consisted of identification and registration records, antimicrobial usage, test-day records from the milk recording program, bulk tank milk (BTM) somatic cell count data and results of diagnostic tests on BTM samples. For each of the 227 herds, the CMI per 100 cows per year was calculated per quarter of the year and was combined with the available herd data. Two models were developed to pre...
Echinococcus granulosus is rare in The Netherlands and most human patients originate from souther... more Echinococcus granulosus is rare in The Netherlands and most human patients originate from southern Europe and Africa, where E. granulosus is still endemic in sheep, cattle, and pigs. Since the accession of some south-eastern European countries to the European Union, a large number of cattle have been imported from this area, according to national import data. The objective of this study was to determine the risk of re-introduction of E. granulosus in The Netherlands via the import of cattle from these endemic areas. The number of infected imported cattle was determined by correcting the number of imported cattle with the national animal prevalence of E. granulosus in the country of origin. In 2007, the number of imported E. granulosus-infected cattle varied from 0 (Cyprus) to 4,934 (Romania, accounting for 90% of all positive cattle). The likelihood of detecting E. granulosus at slaughter is low--we assumed, based on confirmed cases, that only 10% of infected cattle will be detected...
Since 2007, mortality associated with a previously unreported haemorrhagic disease has been obser... more Since 2007, mortality associated with a previously unreported haemorrhagic disease has been observed in young calves in several European countries. The syndrome, which has been named 'bovine neonatal pancytopenia' (BNP), is characterised by thrombocytopenia, leukocytopenia and a panmyelophthisis. A herd-level case-control study was conducted in four BNP affected countries (Belgium, France, Germany and the Netherlands) to identify herd management risk factors for BNP occurrence. Data were collected using structured face-to-face and telephone interviews of farm managers and their local veterinarians. In total, 363 case farms and 887 control farms were included in a matched multivariable conditional logistic regression analysis. Case-control status was strongly associated with the odds of herd level use of the vaccine PregSure® BVD (PregSure, Pfizer Animal Health) (matched adjusted odds ratio (OR) 107.2; 95% CI: 41.0-280.1). This was also the case for the practices of feeding c...
Ignoring the limited precision of diagnostic tests can incur serious bias in prevalence (P) estim... more Ignoring the limited precision of diagnostic tests can incur serious bias in prevalence (P) estimation. Most studies treat the sensitivity (SE) and specificity (SP) of the tests as constants. This will result in an underestimation of the variability of P. Bayesian inference provides a natural framework with which to integrate the variability in the estimates of SE and SP with estimation of P.1
In the Netherlands, the feasibility of a national control program for infectious bovine rhinotrac... more In the Netherlands, the feasibility of a national control program for infectious bovine rhinotracheitis (IBR) is discussed. The aim of this program would be to achieve freedom from BoHV1 circulation (the causal agent of IBR), in the Dutch cattle population. When IBR would be eradicated, maintaining the free status is essential and insight in the probability of introduction of IBR through cattle imports is crucial. Values for input parameters such as the number of imports per country of origin, herd level prevalence and probability that a random imported animal per age category was either acutely or latently infected with IBR were quantified. A stochastic simulation model was built to predict the basic risk and the efficacy of four risk mitigating scenarios were evaluated. These scenarios involved testing prior to import, import restrictions and vaccination. The model output predicted that IBR infected animals are imported regularly. In an IBR free situation, 571 (5th and 95th percen...
Porcine epidemic diarrhea virus (PEDV) is the highly contagious, causative agent of an economical... more Porcine epidemic diarrhea virus (PEDV) is the highly contagious, causative agent of an economically important acute enteric disease in pigs of all ages. The disease is characterized by diarrhea and dehydration causing mortality and growth retardation. In the last few decades, only classical PEDV was reported sporadically in Europe, but in 2014 outbreaks of PEDV were described in Germany. Phylogenetic analysis showed a very high nucleotide similarity with a variant of PEDV that was isolated in the US in January 2014. The epidemiological situation of PEDV infections in the Netherlands in 2014 was unknown and a seroprevalence study in swine was performed. In total, 838 blood samples from sows from 267 farms and 101 samples from wild boars were collected from May till November 2014 and tested for antibodies against PEDV by ELISA. The apparent herd prevalence of 0.75% suggests that PEDV was not circulating on a large scale in the Netherlands at this time. However, in November 2014 a clin...
Animal health surveillance enables the detection and control of animal diseases including zoonose... more Animal health surveillance enables the detection and control of animal diseases including zoonoses. Under the EU-FP7 project RISKSUR, a survey was conducted in 11 EU Member States and Switzerland to describe active surveillance components in 2011 managed by the public or private sector and identify gaps and opportunities. Information was collected about hazard, target population, geographical focus, legal obligation, management, surveillance design, risk-based sampling, and multi-hazard surveillance. Two countries were excluded due to incompleteness of data. Most of the 664 components targeted cattle (26·7%), pigs (17·5%) or poultry (16·0%). The most common surveillance objectives were demonstrating freedom from disease (43·8%) and case detection (26·8%). Over half of components applied risk-based sampling (57·1%), but mainly focused on a single population stratum (targeted risk-based) rather than differentiating between risk levels of different strata (stratified risk-based). About...
Animal-based welfare assessment is time consuming and expensive. A promising strategy for improvi... more Animal-based welfare assessment is time consuming and expensive. A promising strategy for improving the efficiency of identifying dairy herds with poorer welfare is to first estimate levels of welfare in herds based on data that are more easily obtained. Our aims were to evaluate the potential of herd housing and management data for estimating the level of welfare in dairy herds, and to estimate the associated reduction in the number of farm visits required for identification of herds with poorer welfare in a population. Seven trained observers collected data on 6 animal-based welfare indicators in a selected sample of 181 loose-housed Dutch dairy herds (herd size: 22 to 211 cows). Severely lame cows, cows with lesions or swellings, cows with a dirty hindquarter, and very lean cows were counted, and avoidance distance was assessed for a sample of cows. Occurrence of displacements (social behavior) was recorded in the whole barn during 120 min of observation. For the same herds, data...
The aim of this study was to evaluate whether it was possible to (1) estimate the clinical mastit... more The aim of this study was to evaluate whether it was possible to (1) estimate the clinical mastitis incidence rate (CMI) for all Dutch dairy herds and (2) to detect farms with a high CMI based on routinely collected herd data. For this study, 240 dairy farms with a conventional milking system that participated in the milk recording program every 4 to 6 wk were randomly selected and agreed to participate. From the initial 240 herds, data of clinical mastitis (CM) registrations and routinely collected herd data of 227 herds were complete and could be used for analysis. Routinely collected herd data consisted of identification and registration records, antimicrobial usage, test-day records from the milk recording program, bulk tank milk (BTM) somatic cell count data and results of diagnostic tests on BTM samples. For each of the 227 herds, the CMI per 100 cows per year was calculated per quarter of the year and was combined with the available herd data. Two models were developed to pre...
Echinococcus granulosus is rare in The Netherlands and most human patients originate from souther... more Echinococcus granulosus is rare in The Netherlands and most human patients originate from southern Europe and Africa, where E. granulosus is still endemic in sheep, cattle, and pigs. Since the accession of some south-eastern European countries to the European Union, a large number of cattle have been imported from this area, according to national import data. The objective of this study was to determine the risk of re-introduction of E. granulosus in The Netherlands via the import of cattle from these endemic areas. The number of infected imported cattle was determined by correcting the number of imported cattle with the national animal prevalence of E. granulosus in the country of origin. In 2007, the number of imported E. granulosus-infected cattle varied from 0 (Cyprus) to 4,934 (Romania, accounting for 90% of all positive cattle). The likelihood of detecting E. granulosus at slaughter is low--we assumed, based on confirmed cases, that only 10% of infected cattle will be detected...
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