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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    Selection and antigenic characterization of immune-escape mutants of H7N2 low pathogenic avian influenza virus using homologous polyclonal sera
    Sitaras, Ioannis ; Spackman, Erica ; Jong, Mart C.M. de; Parris, D.J. - \ 2020
    Virus Research 290 (2020). - ISSN 0168-1702
    Antigenic cartography - Low pathogenic avian influenza - Polyclonal sera - Viral mutant selection - Virus evolution
    Understanding the dynamics of the selection of influenza A immune escape variants by serum antibody is critical for designing effective vaccination programs for animals, especially poultry where large populations have a short generation time and may be vaccinated with high frequency. In this report, immune-escape mutants of A/turkey/New York/4450/1994 H7N2 low pathogenic avian influenza virus, were selected by serially passaging the virus in the presence of continuously increasing concentrations of homologous chicken polyclonal sera. Amino acid mutations were identified by sequencing the parental hemagglutinin (HA) gene and every 10 passages by both Sanger and deep sequencing, and the antigenic distance of the mutants to the parent strain was determined. Progressively, a total of five amino acid mutations were observed over the course of 30 passages. Based on their absence from the parental virus with deep sequencing, the mutations appear to have developed de novo. The antigenic distance between the selected mutants and the parent strain increased as the number of amino acid mutations accumulated and the concentration of antibodies had to be periodically increased to maintain the same reduction in virus titer during selection. This selection system demonstrates how H7 avian influenza viruses behave under selection with homologous sera, and provides a glimpse of their evolutionary dynamics, which can be applied to developing vaccination programs that maximize the effectiveness of a vaccine over time.
    Effects of migration network configuration and migration synchrony on infection prevalence in geese
    Yin, Shenglai ; Knegt, Henrik J. de; Jong, Mart C.M. de; Si, Yali ; Prins, Herbert H.T. ; Huang, Zheng Y.X. ; Boer, Willem F. de - \ 2020
    Journal of Theoretical Biology 502 (2020). - ISSN 0022-5193
    Avian influenza - Cumulative infection - Environmental transmission - SIR model - Stopover site

    Migration can influence dynamics of pathogen-host interactions. However, it is not clearly known how migration pattern, in terms of the configuration of the migration network and the synchrony of migration, affects infection prevalence. We therefore applied a discrete-time SIR model, integrating environmental transmission and migration, to various migration networks, including networks with serial, parallel, or both serial and parallel stopover sites, and with various levels of migration synchrony. We applied the model to the infection of avian influenza virus in a migratory geese population. In a network with only serial stopover sites, increasing the number of stopover sites reduced infection prevalence, because with every new stopover site, the amount of virus in the environment was lower than that in the previous stopover site, thereby reducing the exposure of the migratory population. In a network with parallel stopover sites, both increasing the number and earlier appearance of the stopover sites led to an earlier peak of infection prevalence in the migratory population, because the migratory population is exposed to larger total amount of virus in the environment, speeding-up the infection accumulation. Furthermore, higher migration synchrony reduced the average number of cumulative infection, because the majority of the population can fly to a new stopover site where the amount of virus is still relatively low and has not been increased due to virus shedding of infected birds. Our simulations indicate that a migration pattern with multiple serial stopover sites and with highly synchronized migration reduces the infection prevalence.

    Science talks corona - How contamination works
    Jong, M.C.M. de - \ 2020
    Wageningen University & Research
    Spatial model of Bovine tuberculosis in two-host disease dynamic system in the Republic of Ireland
    Chang, You ; Jong, M.C.M. de - \ 2020
    In: Wias Annual Conference 2020 WIAS - p. 84 - 84.
    Bovine tuberculosis, caused by mycobacterium bovis, is a zoonotic infectious disease mainly in domestic and wild animals. It is a chronic disease, which can cause chronic inflammation,coughing, weight loss and eventual death. It has a huge negative impact onthe economic and animal welfare. The Republic of Ireland has been working on BTB eradication in cattle since 1954 and has spent an accumulative expenditure of over €5.5 billion.Although there is an ongoing decline, the herd prevalence of bovine tuberculosis has remained steady of around 5%. The previous control strategy test-and-removal on cattle was not sufficient to eradicate tuberculosis in the Republic of Ireland because badgers play a role in the transmission. This cross-species transmission has been proved by field trials which showed a link between badgers culling and reduction in cattle BTB incidence. Until very recently, badger vaccination was added to the control policy and is being rolled out across the country. However, researchers and policymakers are still unsure whether current control policy (test-and-removal plus badger vaccination) is sufficient to eradicate bovine tuberculosis in 2030.Therefore, this PhD project aims to understand better the spatial heterogeneity of BTB transmission in the Republic of Ireland by using mathematical and statistical models. In this study, we want to provide a model to generate risk maps and find the relative contribution of each transmission routes. To achieve the final goal step by step,we will develop several research objectives to have an advanced understanding of BTB transmission. Firstly, we will develop a new method to quantify indirect transmission without observing environmental data and evaluate this method by a simulation study. Then, we will develop a method to quantify transmission in a two-host system in the spatial context by combining transmission kernels with next generation matrix method. This method will be used to analyze field data and eventually generate a reproduction ratio map for the whole country. Lastly, a dynamical model will be developed to disentangle the relative importance of each transmission mechanism in BTB spread and estimate the cost-effectiveness of interventions on different transmission routes.
    The evolutionary dynamics of LPAI H9N2 virus circulating in vaccinated and unvaccinated poultry
    Cui, Hongrui ; Jong, M.C.M. de; Beerens, N. ; Oers, M.M. van - \ 2020
    In: Wias Annual Conference 2020 WIAS - p. 67 - 67.
    There are two problems with avian influenza (AI) virus that cause flu in poultry: pathogenicity in poultry and possible effects on human health. Different from the high pathogenic avian influenza (HPAI), the outbreaks of low pathogenic avian influenza (LPAI) that occurred among wild birds naturally, and causing no symptoms or only mild disease in poultry.It seems less severe but deserves sufficient attention as well. In some countries promoting vaccination policy (including China), the avian influenza vaccines used in poultry are increasingly used at a large-scale and long-term. This might force AI viruses to escape the immunity from the current-used vaccine. As a typical LPAI, H9N2 subtype AI virus is frequently isolated and widespread in China. Besides, for domestic poultries, the H9N2 subtype AIviruses could circulate in the host population for a long time. In this period, it has a good chance to mutate, adapt further to the host and escape the immunity. In addition, the long-term vaccination in commercial poultry determines the immunity encountered by the viruses and thus already triggered the antigenic drift. However, information on the impact of poultry vaccination on the evolutionary dynamics of AI viruses in the field is limited. In this research project, we will study the role of virus evolution in the failing vaccination program against H9N2 viruses in China. We are curious that if these evolutionary patterns could help generate the immune-escape strains.
    Quantification of local bovine tuberculosis (bTB) transmission in badgers and cattle with and without vaccination of badgers (Meles Meles) in the Republic of Ireland (RoI)
    Barber, Ann ; Jong, M.C.M. de - \ 2020
    In: Wias Annual Conference 2020. - WIAS - p. 53 - 53.
    In the Republic of Ireland (RoI), bovine Tuberculosis (bTB) in cattle continues to circulate despite considerable efforts placed on controlling the infection. The European badger (Meles meles) is considered by most scientist to be implicit in the transmission and maintenance of bTB in cattle. Badger culling has been linked to a reduction in bTB incidence in cattle, however, continued persecution of badger populations is not sustainable long-term. As an alternative badger intramuscular Bacille Calmette-Guérin (BCG) vaccination is now being rolled out across the country on a phased basis. Although vaccination was associated with a reduction in badger-to-badger transmission in a field trial, it remains un-clear whether vaccination will sufficiently reduce transmission across the badger-cattle system everywhere in the RoI when combined with current control measures in cattle. The objective of this study is to assess the efficacy of the vaccination programme on the multi-host system at a local level. We propose to quantify the spatiotemporal heterogeneity of bTB transmission in a multi-host system (badgers and cattle) across areas with vaccinated and unvaccinated badger populations. We aim to identify any factors that could be involved in limiting the success of badger vaccination so as these limitations may be quickly and adequately addressed by policy decision-makers. Transmission kernels, as a function of distance between epidemiological units (both farms and setts), will be generated for each pairwise unit interaction and these kernels will inform a Next Generation Matrix (NGM) applied to each Quartile (1.5X2km2 grid cells) in the RoI. This will generate a risk map of local (Quartile level) reproduction ratios (R-map). Clusters, hotspots and outliers can be identified via the R-map, informing decision makers about areas which require further in-tervention, where infection cannot be maintained and where the vaccination is proving effective or ineffective. A large body of existing national data will be utilized for the analysis. Further data will be collected in vaccinated regions to monitor the infection status of badger setts over time to inform the transmission kernels, assessing whether or not any reduction in badger transmission of bTB due to vaccination can be accurately attributed to vaccination (or not). The results of this study will provide insights to the policy-makers, i.e. mainly the veterinary services, and by improving the eradication will benefit animal welfare, human health and the profitability of cattle farming.
    Genetic parameters and genomic breeding values for digital dermatitis in Holstein Friesian dairy cattle: Host susceptibility, infectivity and the basic reproduction ratio
    Biemans, Floor ; Jong, Mart C.M. De; Bijma, Piter - \ 2019
    Genetics, Selection, Evolution 51 (2019)1. - ISSN 0999-193X

    Background: For infectious diseases, the probability that an animal gets infected depends on its own susceptibility, and on the number of infectious herd mates and their infectivity. Together with the duration of the infectious period, susceptibility and infectivity determine the basic reproduction ratio of the disease ($ R_{0} $ R 0). $ R_{0} $ R 0 is the average number of secondary cases caused by a typical infectious individual in an otherwise uninfected population. An infectious disease dies out when $ R_{0} $ R 0 is lower than 1. Thus, breeding strategies that aim at reducing disease prevalence should focus on reducing $ R_{0} $ R 0, preferably to a value lower than 1. In animal breeding, however, $ R_{0} $ R 0 has received little attention. Here, we estimate the additive genetic variance in host susceptibility, host infectivity, and $ R_{0} $ R 0 for the endemic claw disease digital dermatitis (DD) in Holstein Friesian dairy cattle, and estimate genomic breeding values (GEBV) for these traits. We recorded DD disease status of both hind claws of 1513 cows from 12 Dutch dairy farms, every 2 weeks, 11 times. The genotype data consisted of 75,904 single nucleotide polymorphisms (SNPs) for 1401 of the cows. We modelled the probability that a cow got infected between recordings, and compared four generalized linear mixed models. All models included a genetic effect for susceptibility; Models 2 and 4 also included a genetic effect for infectivity, while Models 1 and 2 included a farm*period interaction. We corrected for variation in exposure to infectious herd mates via an offset. Results: GEBV for $ R_{0} $ R 0 from the model that included genetic effects for susceptibility only had an accuracy of ~ 0.39 based on cross-validation between farms, which is very high given the limited amount of data and the complexity of the trait. Models with a genetic effect for infectivity showed a larger bias, but also a slightly higher accuracy of GEBV. Additive genetic standard deviation for $ R_{0} $ R 0 was large, i.e. ~ 1.17, while the mean $ R_{0} $ R 0 was 2.36. Conclusions: GEBV for $ R_{0} $ R 0 showed substantial variation. The mean $ R_{0} $ R 0 was only about one genetic standard deviation greater than 1. These results suggest that lowering DD prevalence by selective breeding is promising.

    Virus Shedding of Avian Influenza in Poultry: A Systematic Review and Meta-Analysis
    Germeraad, Evelien A. ; Sanders, Pim ; Hagenaars, Thomas J. ; Jong, Mart C.M. de; Beerens, Nancy ; Gonzales, Jose L. - \ 2019
    Viruses 11 (2019)9. - ISSN 1999-4915
    avian influenza - meta-analysis - poultry - systematic review - virus shedding

    Understanding virus shedding patterns of avian influenza virus (AIV) in poultry is important for understanding host-pathogen interactions and developing effective control strategies. Many AIV strains were studied in challenge experiments in poultry, but no study has combined data from those studies to identify general AIV shedding patterns. These systematic review and meta-analysis were performed to summarize qualitative and quantitative information on virus shedding levels and duration for different AIV strains in experimentally infected poultry species. Methods were designed based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Four electronic databases were used to collect literature. A total of 1155 abstract were screened, with 117 studies selected for the qualitative analysis and 71 studies for the meta-analysis. A large heterogeneity in experimental methods was observed and the quantitative analysis showed that experimental variables such as species, virus origin, age, inoculation route and dose, affect virus shedding (mean, peak and duration) for highly pathogenic AIV (HPAIV), low pathogenic AIV (LPAIV) or both. In conclusion, this study highlights the need to standardize experimental procedures, it provides a comprehensive summary of the shedding patterns of AIV strains by infected poultry and identifies the variables that influence the level and duration of AIV shedding.

    Preparing for Virus X
    Kortekaas, J.A. ; Poel, W.H.M. van der; Jong, M.C.M. de - \ 2019
    Quantifying transmission of Mycobacterium avium subsp. paratuberculosis among group-housed dairy calves
    Corbett, Caroline S. ; Jong, Mart C.M. De; Orsel, Karin ; Buck, Jeroen De; Barkema, Herman W. - \ 2019
    Veterinary Research 50 (2019)1. - ISSN 0928-4249

    Johne's disease (JD) is a chronic enteritis caused by Mycobacterium avium subsp. paratuberculosis (MAP), with control primarily aimed at preventing new infections among calves. The aim of the current study was to quantify calf-to-calf transmission of MAP among penmates in an experimental trial. Newborn Holstein bull calves (n = 32) were allocated into pens of 4, with 2 inoculated (IN) calves and 2 calves that were contact exposed (CE). Calves were group-housed for 3 months, with frequent collection of fecal and blood samples and tissue collection after euthanasia. The basic reproduction ratio (R0) was estimated using a final size (FS) model with a susceptible-infected model, based on INF-γELISA and tissue culture followed by qPCR. In addition, the transmission rate parameter (β) for new shedding events was estimated using a general linearized method (GLM) model with a susceptible-infected-susceptible model based on culture, followed by qPCR, of fecal samples collected during group housing. The R0 was derived for IN and CE calves separately, due to a difference in susceptibility, as well as differences in duration of shedding events. Based on the FS model, interferon-γresults from blood samples resulted in a R 0 IG of 0.90 (0.24, 2.59) and tissue culture resulted in a R 0 T of 1.36 (0.45, 3.94). Based on the GLM model, the R0 for CE calves to begin shedding (R 0 CE) was 3.24 (1.14, 7.41). We concluded that transmission of MAP infection between penmates occurred and that transmission among calves may be an important cause of persistent MAP infection on dairy farms that is currently uncontrolled for in current JD control programs.

    A genome-wide association study for susceptibility and infectivity of Holstein Friesian dairy cattle to digital dermatitis
    Biemans, F. ; Jong, M.C.M. de; Bijma, P. - \ 2019
    Journal of Dairy Science 102 (2019)7. - ISSN 0022-0302 - p. 6248 - 6262.
    claw health - generalized linear mixed model - genetic parameter - heritability - transmission

    Selection and breeding can be used to fight transmission of infectious diseases in livestock. The prevalence in a population depends on the susceptibility and infectivity of the animals. Knowledge on the genetic background of those traits would facilitate efficient selection for lower disease prevalence. We investigated the genetic background of host susceptibility and infectivity for digital dermatitis (DD), an endemic infectious claw disease in dairy cattle, with a genome-wide association study (GWAS), using either a simple linear mixed model or a generalized linear mixed model based on epidemiological theory. In total, 1,513 Holstein-Friesian cows of 12 Dutch dairy farms were scored for DD infection status and class (M0 to M4.1) every 2 wk for 11 times; 1,401 of these cows were genotyped with a 75k SNP chip. We performed a GWAS with a linear mixed model on 10 host disease status traits, and with a generalized linear mixed model with a complementary log-log link function (GLMM) on the probability that a cow would get infected between 2 scorings. With the GLMM, we fitted SNP effects for host susceptibility and host infectivity, while taking the variation in exposure of the susceptible cow to infectious herd mates into account. With the linear model we detected 4 suggestive SNP (false discovery rate < 0.20), 2 for the fraction of observations a cow had an active lesion on chromosomes 1 and 14, one for the fraction of observations a cow had an M2 lesion on at least one claw on chromosome 1 (the same SNP as for the fraction of observations with an active lesion), and one for the fraction of observations a cow had an M4.1 lesion on at least one claw on chromosome 10. Heritability estimates ranged from 0.09 to 0.37. With the GLMM we did not detect significant nor suggestive SNP. The SNP effects on disease status analyzed with the linear model had a correlation coefficient of only 0.70 with SNP effects on susceptibility of the GLMM, indicating that both models capture partly different effects. Because the GLMM better accounts for the epidemiological mechanisms determining individual disease status and for the distribution of the y-variable, results of the GLMM may be more reliable, despite the absence of suggestive associations. We expect that with an extended GLMM that better accounts for the full genetic variation in infectivity via the environment, the accuracy of SNP effects may increase.

    The economic value of R0 for macroparasitic diseases
    Janssen, K.P.E. ; Saatkamp, H.W. ; Bijma, P. ; Jong, M.C.M. de; Komen, J. - \ 2018
    In: Proceedings of the World Congress on Genetics Applied to Livestock Production. - WCGALP - 8 p.
    Economic values are used to balance the emphasis on breeding goal traits, and determine whether selection for a trait is worthwhile. The basic reproduction ratio (R0) determines transmission dynamics of a disease and, therefore, R0 is an appropriate breeding goal trait. This study presents an easy to use framework for the derivation of the economic value of R0 for macroparasitic diseases. An example for sea lice in salmon is provided, resulting in an estimate of R0 of 2.9 with an economic value of -0.072 €/unit R0/kg production. Keywords: Economic value, R0, epidemiology, disease
    Derivation of the economic value of r0 for macroparasites: application to sea lice in salmon
    Janssen, K.P.E. ; Komen, J. ; Saatkamp, H.W. ; Jong, M.C.M. de; Bijma, P. - \ 2018
    Posternummer SBQ8
    A new model to Calibrate a Reference Standard for bovine tuberculin purified protein derivative in the target species
    Frankena, Klaas ; Jacobs, Liesbeth ; Dijk, Tonny van; Good, Margaret ; Duignan, Anthony ; Jong, Mart C.M. de - \ 2018
    Frontiers in Veterinary Science 5 (2018)OCT. - ISSN 2297-1769
    Bovine international standard - Cattle - Guinea pigs - Mycobacterium bovis - New reference standard - Potency estimation - Tuberculin

    Since 1986, use of a Bovine International Standard (BIS) for bovine tuberculin has been required to ensure national and international uniformity regarding the potency designation of bovine tuberculin Purified Protein Derivative (PPDb) preparations produced by multiple manufacturers. The BIS is the unique golden standard in the guinea pig potency assay, representing 100% potency, where potencies of production batches are calculated as relative potencies in comparison with the potency of the BIS which was set at 32,500 international Unit (IU) per mg. The stock supply and lifetime of the BIS is limited.The aim of this study was to develop a model to determine the potency of a newly produced in-house Reference Standard (RS) for PPDb with great accuracy in the target species (cattle) and to prove its precision and accuracy in the guinea pig potency test. First simulations were done to estimate the required number of cattle needed. Then, 30 naturally bTB infected cattle were subjected to a tuberculin skin test using multiple injections of both the RS and the BIS. Both were applied randomly in the same volume and concentration (1 dose). The potency of the RS against the BIS was directly derived from the least square means (LSMEANS) and was estimated as 1.067 (95% CI: 1.025-1.109), equal to a potency of 34,700 ± 1,400 IU/mg. In six guinea pig potency assays the RS was used to assign potencies to production batches of PPDb. Here, precision and accuracy of the RS was determined according to the parallel-line assay. Relative potencies were estimated by exponentiation of the common slope. The corresponding 95% confidence intervals were obtained according to Fieller's theorem. In sensitized guinea pigs, the relative potency of the RS against the BIS was 1.115 (95% CI: 0.871-1.432), corresponding to an absolute potency of 36,238 IU/mg (95% CI: 28,308-46,540).In conclusion: the method used to determine the potency of the RS against the BIS in naturally bTB infected cattle, resulted in a highly accurate potency estimate of the RS. The RS can be used in the guinea pig test to assign potencies to PPDb production batches with high precision and accuracy.

    Derivation of the economic value of R0 for macroparasitic diseases and application to sea lice in salmon
    Janssen, Kasper ; Komen, Hans ; Saatkamp, Helmut W. ; Jong, Mart C.M. de; Bijma, Piter - \ 2018
    Genetics, Selection, Evolution 50 (2018)1. - ISSN 0999-193X

    Background: Macroparasites, such as ticks, lice, and helminths, are a concern in livestock and aquaculture production, and can be controlled by genetic improvement of the host population. Genetic improvement should aim at reducing the rate at which parasites spread across the farmed population. This rate is determined by the basic reproduction ratio, i.e. R 0, which is the appropriate breeding goal trait. This study aims at providing a method to derive the economic value of R 0. Methods: Costs of a disease are the sum of production losses and expenditures on disease control. Genetic improvement of R 0 lowers the loss-expenditure frontier. Its economic effect depends on whether the management strategy is optimized or not. The economic value may be derived either from the reduction in losses with constant expenditures or from the reduction in expenditures with constant losses. Results: R 0 ≤ 1, the economic value of a further reduction is zero because there is no risk of a major epidemic. When R 0 > 1 and management is optimized, the economic value increases with decreasing values of R 0, because both the mean number of parasites per host and frequency of treatments decrease at an increasing rate when R 0 decreases. When R 0 > 1 and management is not optimized, the economic value depends on whether genetic improvement is used for reducing expenditures or losses. For sea lice in salmon, the economic value depends on a reduction in expenditures with constant losses, and is estimated to be 0.065€/unit R 0 /kg production. Discussion: Response to selection for measures of disease prevalence cannot be predicted from quantitative genetic theory alone. Moreover, many studies fail to address the issue of whether genetic improvement results in reduced losses or expenditures. Using R 0 as the breeding goal trait, weighed by its appropriate economic value, avoids these issues. Conclusion: When management is optimized, the economic value increases with decreasing values of R 0 (until the threshold R 0 = 1, where it drops to zero). When management is not optimized, the economic value depends on whether genetic improvement is used for reduced expenditures or production losses. For sea lice in salmon, the economic value is estimated to be 0.065 €/unit R 0 /kg production.

    Seroprevalence and risk factors of lumpy skin disease in Ethiopia
    Molla, Wassie ; Frankena, Klaas ; Gari, Getachew ; Kidane, Menbere ; Shegu, Dereje ; Jong, Mart C.M. de - \ 2018
    Preventive Veterinary Medicine 160 (2018). - ISSN 0167-5877 - p. 99 - 104.
    Capripoxvirus - Cattle - Ethiopia - Lumpy skin disease - Risk factors - Seroprevalence

    Lumpy skin disease (LSD) is an acute or inapparent viral disease of cattle which is endemic in many African and Middle East countries. LSD is one of the major transboundary livestock diseases in Ethiopia. A cross-sectional study using multistage cluster sampling was undertaken in central and north-western parts of Ethiopia with the objectives to estimate seroprevalence and to identify and quantify risk factors contributing to the occurrence of the disease. A total of 2386 cattle sera were sampled from 605 herds and 30 clusters (kebeles) located in 10 districts and tested for presence of LSD virus antibodies using virus neutralization test. All the serum samples were collected from cattle having no history of LSD vaccination. The overall animal level and herd level apparent seroprevalences were 25.4% (95% CI: 23.7–27.2) and 48.9% (95% CI: 44.9-52.9), respectively and varied significantly between districts. The true animal level and herd level prevalences were estimated as 26.5% (95% CI: 24.7–28.3) and 52.6% (95% CI: 48.3–56.9), respectively. At animal level, adult age (OR = 2.44 (95% CI: 1.67–3.55) compared to calf), contact with other animals (OR = 0.41 (95% CI: 0.23-0.74), compared to no contact) and presence of water bodies (OR = 1.61 (95% CI: 1.03–2.52), compared to no such bodies) were identified as the most important risk factors in relation to testing LSD positive. The putative risk factors altitude, breed, sex, and presence of animal trade route showed no significant association with LSD sero-status. Generally, cattle population with many adult animals and that live in wet areas are at highest risk, whereas cattle in frequent contact with other animals and animal species have lower risk, potentially due to a dilution effect of vectors.

    The intractable challenge of evaluating cattle vaccination as a control for bovine tuberculosis
    Conlan, Andrew James Kerr ; Vordermeier, Martin ; Jong, Mart C.M. de; Wood, James L.N. - \ 2018
    eLife 7 (2018). - ISSN 2050-084X

    Vaccination of cattle against bovine Tuberculosis (bTB) has been a long-term policy objective for countries where disease continues to persist despite costly test-and-slaughter programs. The potential use of vaccination within the European Union has been linked to a need for field evaluation of any prospective vaccine and the impact of vaccination on the rate of transmission of bTB. We calculate that estimation of the direct protection of BCG could be achieved with 100 herds, but over 500 herds would be necessary to demonstrate an economic benefit for farmers whose costs are dominated by testing and associated herd restrictions. However, the low and variable attack rate in GB herds means field trials are unlikely to be able to discern any impact of vaccination on transmission. In contrast, experimental natural transmission studies could provide robust evaluation of both the efficacy and mode of action of vaccination using as few as 200 animals.

    Digital Dermatitis in dairy cattle : The contribution of different disease classes to transmission
    Biemans, Floor ; Bijma, Piter ; Boots, Natasja M. ; Jong, Mart C.M. de - \ 2018
    Epidemics 23 (2018). - ISSN 1755-4365 - p. 76 - 84.
    Basic reproduction ratio - Cow - Hairy heel wrat - Infection - Infectivity - Mortellaro
    Digital Dermatitis (DD) is a claw disease mainly affecting the hind feet of dairy cattle. Digital Dermatitis is an infectious disease, transmitted via the environment, where the infectious "agent" is a combination of bacteria. The standardized classification for DD lesions developed by Döpfer et al. (1997) and extended by Berry et al. (2012) has six distinct classes: healthy (M0), an active granulomatous area of 0-2 cm (M1), an ulcerative lesion of >2 cm (M2), an ulcerative lesion covered by a scab (M3), alteration of the skin (M4), and a combination of M4 and M1 (M4.1).We hypothesize that classes M1, M2, M3, M4, and M4.1 are the potentially infectious classes that can contribute to the basic reproduction ratio (R0), the average number of new infections caused by a typical infected individual. Here, we determine differences in infectivity between the classes, the sojourn time in each of the classes, and the contribution of each class to R0. The analysis is based on data from twelve farms in the Netherlands that were visited every two weeks, eleven times.We found that 93.89% of the transitions from M0 was observed as a transition to class M4, and feet with another class-at-infection rapidly transitioned to class M4. As a consequence, about 70% of the infectious time was spent in class M4. Transmission rate parameters of class-at-infection M1, M2, M3, and M4 were not significantly different from each other, but differed from class-at-infection M4.1. However, due to the relative large amount of time spend in class M4, regardless of the class-at-infection, R0 was almost completely determined by this class. The R0 was 2.36, to which class-at-infection M4 alone contributed 88.5%.Thus, M4 lesions should be prevented to lower R0 to a value below one, while painful M2 lesions should be prevented for animal welfare reasons.
    Quantification of Mycobacterium bovis transmission in a badger vaccine field trial
    Aznar, I. ; Frankena, K. ; More, S.J. ; O'Keeffe, J. ; McGrath, G. ; Jong, M.C.M. de - \ 2018
    Preventive Veterinary Medicine 149 (2018). - ISSN 0167-5877 - p. 29 - 37.
    Bacille calmette-Guérin (BCG) - Badgers - Basic reproduction ratio - Mycobacterium bovis - Transmission - Vaccine efficacy for infectiousness - Vaccine efficacy for susceptibility
    In the UK and Ireland, Bacille Calmette-Guérin (BCG) vaccination of badgers has been suggested as one of a number of strategies to control or even eradicate Mycobacterium bovis infection in badgers. In this manuscript, we present the results of a badger field trial conducted in Ireland and discuss how the novel trial design and analytical methods allowed the effects of vaccination on protection against infection and, more importantly, on transmission to be estimated. The trial area was divided into three zones North to South (A, B and C) where vaccination coverages of 0, 50 and 100%, respectively, were applied. Badgers were trapped over a 4 year period. Badgers were assigned to either placebo or vaccine treatment, with treatment allocation occurring randomly in zone B. Blood samples were collected at each capture, and serology was performed in these samples using a chemiluminescent multiplex ELISA system (Enfer test). The analysis aimed to compare new infections occurring in non-infected non-vaccinated badgers to those in non-infected vaccinated ones, while accounting for the zone in which the badger was trapped and the infection pressure to which this individual badger was exposed. In total, 440 records on subsequent trappings of individual non-infected badgers were available for analysis. Over the study period, 55 new infections occurred in non-vaccinated (out of 239 = 23.0%) and 40 in vaccinated (out of 201 = 19.9%) badgers. A Generalized Linear Model (GLM) with a cloglog link function was used for analysis. Statistical analysis showed that susceptibility to natural exposure with M. bovis was reduced in vaccinated compared to placebo treated badgers: vaccine efficacy for susceptibility, VES, was 59% (95% CI = 6.5%–82%). However, a complete lack of effect from BCG vaccination on the infectivity of vaccinated badgers was observed, i.e. vaccine efficacy for infectiousness (VEI) was 0%. Further, the basic reproduction ratio as a function of vaccination coverage (p) (i.e. R(p)) was estimated. Given that the prevalence of M. bovis infection in badgers in endemic areas in Ireland is approximately 18%, we estimated the reproduction ratio in the unvaccinated population as R(0) = 1.22. Because VES was now known, the reproduction ratio for a fully vaccinated population was estimated as R(1) = 0.50. These results imply that with vaccination coverage in badgers exceeding 30%, eradication of M. bovis in badgers in Ireland is feasible, provided that the current control measures also remain in place.
    Temporal and spatial distribution of lumpy skin disease outbreaks in Ethiopia in the period 2000 to 2015
    Molla, W. ; Jong, M.C.M. de; Frankena, K. - \ 2017
    BMC Veterinary Research 13 (2017)1. - ISSN 1746-6148
    Ethiopia - Forecast - Lumpy skin disease - Spatial - Temporal - Time series
    Background: Lumpy skin disease (LSD) is an infectious viral disease of cattle caused by a virus of the genus Capripoxvirus. LSD was reported for the first time in Ethiopia in 1981 and subsequently became endemic. This time series study was undertaken with the aims of identifying the spatial and temporal distribution of LSD outbreaks and to forecast the future pattern of LSD outbreaks in Ethiopia. Results: A total of 3811 LSD outbreaks were reported in Ethiopia between 2000 and 2015. In this period, LSD was reported at least once in 82% of the districts (n = 683), 88% of the administrative zones (n = 77), and all of the regional states or city administrations (n = 9 and n = 2) in the country. The average incidence of LSD outbreaks at district level was 5.58 per 16 years (0.35 year-1). The incidence differed between areas, being the lowest in hot dry lowlands and highest in warm moist highland. The occurrence of LSD outbreaks was found to be seasonal. LSD outbreaks generally have a peak in October and a low in May. The trend of LSD outbreaks indicates a slight, but statistically significant increase over the study period. The monthly precipitation pattern is the reverse of LSD outbreak pattern and they are negatively but non-significantly correlated at lag 0 (r = -0.05, p = 0.49, Spearman rank correlation) but the correlation becomes positive and significant when the series are lagged by 1 to 6 months, being the highest at lag 3 (r = 0.55, p < 0.001). The forecast for the period 2016-2018 revealed that the highest number of LSD outbreaks will occur in October for all the 3 years and the lowest in April for the year 2016 and in May for 2017 and 2018. Conclusion: LSD occurred in all major parts of the country. Outbreaks were high at the end of the long rainy season. Understanding temporal and spatial patterns of LSD and forecasting future occurrences are useful for indicating periods when particular attention should be paid to prevent and control the disease.
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