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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    Tripartite interactions among Ixodiphagus hookeri, ixodes ricinus and deer : Differential interference with transmission cycles of tick-borne pathogens
    Krawczyk, Aleksandra I. ; Bakker, Julian W. ; Koenraadt, Constantianus J.M. ; Fonville, Manoj ; Takumi, Katsuhisa ; Sprong, Hein ; Demir, Samiye - \ 2020
    Pathogens 9 (2020)5. - ISSN 2076-0817
    Biological control - Host preference - Human granulocytic anaplasmosis - Lyme borreliosis - Neoehrlichiosis - Parasitic wasp - Parasitization - Tick-borne pathogen - Transmission cycle

    For the development of sustainable control of tick-borne diseases, insight is needed in biological factors that affect tick populations. Here, the ecological interactions among Ixodiphagus hookeri, Ixodes ricinus, and two vertebrate species groups were investigated in relation to their effects on tick-borne disease risk. In 1129 questing ticks, I. hookeri DNA was detected more often in I. ricinus nymphs (4.4%) than in larvae (0.5%) and not in adults. Therefore, we determined the infestation rate of I. hookeri in nymphs from 19 forest sites, where vertebrate, tick, and tick-borne pathogen communities had been previously quantified. We found higher than expected co-occurrence rates of I. hookeri with deer-associated Anaplasma phagocytophilum, and lower than expected rates with rodent-associated Borrelia afzelii and Neoehrlichia mikurensis. The prevalence of I. hookeri in nymphs varied between 0% and 16% and was positively correlated with the encounter probability of ungulates and the densities of all life stages of I. ricinus. Lastly, we investigated the emergence of I. hookeri from artificially fed, field-collected nymphs. Adult wasps emerged from seven of the 172 fed nymphs. From these observations, we inferred that I. hookeri is parasitizing I. ricinus larvae that are feeding on deer, rather than on rodents or in the vegetation. Since I. hookeri populations depend on deer abundance, the main propagation host of I. ricinus, these wasps have no apparent effect on tick populations. The presence of I. hookeri may directly interfere with the transmission cycle of A. phagocytophilum, but not with that of B. afzelii or N. mikurensis.

    A retain and refine approach to cumulative risk assessment
    Kennedy, Marc C. ; Hart, Andy D.M. ; Kruisselbrink, Johannes W. ; Lenthe, Marco van; Boer, Waldo J. de; Voet, Hilko van der; Rorije, Emiel ; Sprong, Corinne ; Klaveren, Jacob van - \ 2020
    Food and Chemical Toxicology 138 (2020). - ISSN 0278-6915
    Cumulative assessment group - Mixtures - Pesticides - QSAR - Relative potency factor - Uncertainty

    Mixtures of substances to which humans are exposed may lead to cumulative exposure and health effects. To study their effects, it is first necessary to identify a cumulative assessment group (CAG) of substances for risk assessment or hazard testing. Excluding substances from consideration before there is sufficient evidence may underestimate the risk. Conversely, including everything and treating the inevitable uncertainties using conservative assumptions is inefficient and may overestimate the risk, with an unknown level of protection. An efficient, transparent strategy is described to retain a large group, quantifying the uncertainty of group membership and other uncertainties. Iterative refinement of the CAG then focuses on adding information for the substances with high probability of contributing significantly to the risk. Probabilities can be estimated using expert opinion or derived from data on substance properties. An example is presented with 100 pesticides, in which the retain step identified a single substance to target refinement. Using an updated hazard characterisation for this substance reduced the mean exposure estimate from 0.43 to 0.28 μg kg-bw−1 day−1 and reduced the 99.99th percentile exposure from 24.9 to 5.1 μg kg-bw−1 day−1. Other retained substances contributed little to the risk estimates, even after accounting for uncertainty.

    The MCRA toolbox of models and data to support chemical mixture risk assessment
    Voet, Hilko van der; Kruisselbrink, Johannes W. ; Boer, Waldo J. de; Lenthe, Marco S. van; Heuvel, J.J.B. van den; Crépet, Amélie ; Kennedy, Marc C. ; Zilliacus, Johanna ; Beronius, Anna ; Tebby, Cleo ; Brochot, Céline ; Luckert, Claudia ; Lampen, Alfonso ; Rorije, Emiel ; Sprong, Corinne ; Klaveren, Jacob D. van - \ 2020
    Food and Chemical Toxicology 138 (2020). - ISSN 0278-6915
    Exposure - Hazard - Mixtures - Probabilistic model - Risk assessment - Software

    A model and data toolbox is presented to assess risks from combined exposure to multiple chemicals using probabilistic methods. The Monte Carlo Risk Assessment (MCRA) toolbox, also known as the EuroMix toolbox, has more than 40 modules addressing all areas of risk assessment, and includes a data repository with data collected in the EuroMix project. This paper gives an introduction to the toolbox and illustrates its use with examples from the EuroMix project. The toolbox can be used for hazard identification, hazard characterisation, exposure assessment and risk characterisation. Examples for hazard identification are selection of substances relevant for a specific adverse outcome based on adverse outcome pathways and QSAR models. Examples for hazard characterisation are calculation of benchmark doses and relative potency factors with uncertainty from dose response data, and use of kinetic models to perform in vitro to in vivo extrapolation. Examples for exposure assessment are assessing cumulative exposure at external or internal level, where the latter option is needed when dietary and non-dietary routes have to be aggregated. Finally, risk characterisation is illustrated by calculation and display of the margin of exposure for single substances and for the cumulation, including uncertainties derived from exposure and hazard characterisation estimates.

    Effects of cattle grazing on Ixodes ricinus-borne disease risk in forest areas of the Netherlands
    Sprong, Hein ; Moonen, Sander ; Wieren, Sipke E. van; Hofmeester, Tim R. - \ 2020
    Ticks and Tick-borne Diseases 11 (2020)2. - ISSN 1877-959X
    Cross-sectional study - Intervention - Lyme borreliosis - Prevention

    Cattle grazing has been suggested to reduce the risk for Lyme borreliosis by decreasing the density of questing Ixodes ricinus infected with Borrelia burgdorferi sensu lato. We tested the hypotheses that cattle grazing used in woodland management decreases the density of questing I. ricinus, and that it decreases the nympal infection prevalence of B. burgdorferi sensu lato. We further expected the nympal infection prevalence of tick-borne pathogens that utilize cattle as amplifying hosts, namely Anaplasma phagocytophilum, and Babesia sensu stricto, to increase. To test these hypotheses, we compared the densities of questing I. ricinus between twenty pairs of plots in grazed and ungrazed forest areas. The density of I. ricinus adults, but not nymphs, was lower in areas grazed by cattle than in ungrazed areas. Nymphs were tested for the presence of Borrelia burgdorferi s.l., Borrelia miyamotoi, Anaplasma phagocytophilum, and Babesia s.s. DNA from twelve paired areas. Anaplasma phagocytophilum and Babesia s.s. from qPCR-positive tick lysates were identified further to the ecotype and species level, respectively, by DNA sequencing. The infection prevalence of A. phagocytophilum was lower, and infection prevalence of Babesia s.s., identified as Babesia venatorum, was higher in grazed areas. In contrast, infection prevalence with B. burgdorferi s.l. or B. miyamotoi did not differ between grazed and ungrazed areas. As a consequence, conventional cattle grazing in forested areas had no effect on the densities of questing nymphs infected with B. burgdorferi s.l. and B. miyamotoi. Similarly, we found no effect of cattle grazing on the density of infected nymphs with B. venatorum. The marked difference in the densities of questing nymphs infected with A. phagocytophilum could potentially be explained by the presence of a higher density of roe deer (Capreolus capreolus) in ungrazed areas, as the majority of typed A. phagocytophilum from ungrazed areas were the non-zoonotic ecotype II, which is associated with roe deer.

    Effect of rodent density on tick and tick-borne pathogen populations: Consequences for infectious disease risk
    Krawczyk, Aleksandra I. ; Duijvendijk, Gilian L.A. Van; Swart, Arno ; Heylen, Dieter ; Jaarsma, Ryanne I. ; Jacobs, Frans H.H. ; Fonville, Manoj ; Sprong, Hein ; Takken, Willem - \ 2020
    Parasites & Vectors 13 (2020)1. - ISSN 1756-3305
    Disease risk - Ixodes ricinus - Rodent density - Tick-borne pathogens - Transmission dynamics

    Background: Rodents are considered to contribute strongly to the risk of tick-borne diseases by feeding Ixodes ricinus larvae and by acting as amplifying hosts for pathogens. Here, we tested to what extent these two processes depend on rodent density, and for which pathogen species rodents synergistically contribute to the local disease risk, i.e. the density of infected nymphs (DIN). Methods: In a natural woodland, we manipulated rodent densities in plots of 2500 m2 by either supplementing a critical food source (acorns) or by removing rodents during two years. Untreated plots were used as controls. Collected nymphs and rodent ear biopsies were tested for the presence of seven tick-borne microorganisms. Linear models were used to capture associations between rodents, nymphs, and pathogens. Results: Investigation of data from all plots, irrespective of the treatment, revealed a strong positive association between rodent density and nymphal density, nymphal infection prevalence (NIP) with Borrelia afzelii and Neoehrlichia mikurensis, and hence DIN's of these pathogens in the following year. The NIP, but not the DIN, of the bird-associated Borrelia garinii, decreased with increasing rodent density. The NIPs of Borrelia miyamotoi and Rickettsia helvetica were independent of rodent density, and increasing rodent density moderately increased the DINs. In addition, NIPs of Babesia microti and Spiroplasma ixodetis decreased with increasing rodent density, which had a non-linear association with DINs of these microorganisms. Conclusions: A positive density dependence for all rodent- A nd tick-associated tick-borne pathogens was found, despite the observation that some of them decreased in prevalence. The effects on the DINs were variable among microorganisms, more than likely due to contrasts in their biology (including transmission modes, host specificity and transmission efficiency). The strongest associations were found in rodent-associated pathogens that most heavily rely on horizontal transmission. Our results draw attention to the importance of considering transmission mode of a pathogen while developing preventative measures to successfully reduce the burden of disease.

    Assessment of the combined nitrate and nitrite exposure from food and drinking water: application of uncertainty around the nitrate to nitrite conversion factor
    Brand, Annick D. van den; Beukers, Marja ; Niekerk, Maryse ; Donkersgoed, Gerda van; Aa, Monique van der; Ven, Bianca van de; Bulder, Astrid ; Voet, Hilko van der; Sprong, Corinne R. - \ 2020
    Food Additives & Contaminants. Pt. A, Chemistry, Analysis, Control, Exposure & Risk Assessment 37 (2020)4. - ISSN 1944-0049 - p. 568 - 582.
    conversion factor - drinking water - exposure assessment - food additives - Nitrate - nitrite

    Dietary exposure to nitrate and nitrite occurs via three main sources; occurrence in (vegetable) foods, food additives in certain processed foods and contaminants in drinking water. While nitrate can be converted to nitrite in the human body, their risk assessment is usually based on single substance exposure in different regulatory frameworks. Here, we assessed the long-term combined exposure to nitrate and nitrite from food and drinking water. Dutch monitoring data (2012–2018) and EFSA data from 2017 were used for concentration data. These were combined with data from the Dutch food consumption survey (2012–2016) to assess exposure. A conversion factor (median 0.023; range 0.008–0.07) was used to express the nitrate exposure in nitrite equivalents which was added to the nitrite exposure. The uncertainty around the conversion factor was taken into account by using conversion factors randomly sampled from the abovementioned range. The combined dietary exposure was calculated for the Dutch population (1–79 years) with different exposure scenarios to address regional differences in nitrate and nitrite concentrations in drinking water. All scenarios resulted in a combined exposure above the acceptable daily intake for nitrite ion (70 µg/kg bw), with the mean exposure varying between 95–114 µg nitrite/kg bw/day in the different scenarios. Of all ages, the combined exposure was highest in children aged 1 year with an average of 250 µg nitrite/kg bw/day. Vegetables contributed most to the combined exposure in food in all scenarios, varying from 34%–41%. Food additive use contributed 8%–9% to the exposure and drinking water contributed 3%–19%. Our study is the first to perform a combined dietary exposure assessment of nitrate and nitrite while accounting for the uncertain conversion factor. Such a combined exposure assessment overarching different regulatory frameworks and using different scenarios for drinking water is a better instrument for protecting human health than single substance exposure.

    The scale affects our view on the identification and distribution of microbial communities in ticks
    Pollet, Thomas ; Sprong, Hein ; Lejal, Emilie ; Krawczyk, Aleksandra I. ; Moutailler, Sara ; Cosson, Jean Francois ; Vayssier-Taussat, Muriel ; Estrada-Peña, Agustín - \ 2020
    Parasites & Vectors 13 (2020)1. - ISSN 1756-3305 - 1 p.
    Scales - Spatial - Temporal - Tick microbe interactions - Tick microbiome

    Ticks transmit the highest variety of pathogens impacting human and animal health worldwide. It is now well established that ticks also harbour a microbial complex of coexisting symbionts, commensals and pathogens. With the development of high throughput sequencing technologies, studies dealing with such diverse bacterial composition in tick considerably increased in the past years and revealed an unexpected microbial diversity. These data on diversity and composition of the tick microbes are increasingly available, giving crucial details on microbial communities in ticks and improving our knowledge on the tick microbial community. However, consensus is currently lacking as to which scales (tick organs, individual specimens or species, communities of ticks, populations adapted to particular environmental conditions, spatial and temporal scales) best facilitate characterizing microbial community composition of ticks and understanding the diverse relationships among tick-borne bacteria. Temporal or spatial scales have a clear influence on how we conduct ecological studies, interpret results, and understand interactions between organisms that build the microbiome. We consider that patterns apparent at one scale can collapse into noise when viewed from other scales, indicating that processes shaping tick microbiome have a continuum of variability that has not yet been captured. Based on available reports, this review demonstrates how much the concept of scale is crucial to be considered in tick microbial community studies to improve our knowledge on tick microbe ecology and pathogen/microbiota interactions.

    Parasite load and site-specific parasite pressure as determinants of immune indices in two sympatric rodent species
    Hofmeester, Tim R. ; Bügel, Esther J. ; Hendrikx, Bob ; Maas, Miriam ; Franssen, Frits F.J. ; Sprong, Hein ; Matson, Kevin D. - \ 2019
    Animals 9 (2019)12. - ISSN 2076-2615
    Ecological immunology - Haptoglobin - Immune strategy - Natural antibodies - Neutrophil to lymphocyte ratio - Parasitology - Rodents - Vector-borne pathogens - Zoonosis

    Wildlife is exposed to parasites from the environment. This parasite pressure, which differs among areas, likely shapes the immunological strategies of animals. Individuals differ in the number of parasites they encounter and host, and this parasite load also influences the immune system. The relative impact of parasite pressure vs. parasite load on different host species, particularly those implicated as important reservoirs of zoonotic pathogens, is poorly understood. We captured bank voles (Myodes glareolus) and wood mice (Apodemus sylvaticus) at four sites in the Netherlands. We sampled sub-adult males to quantify their immune function, infestation load for ecto-and gastrointestinal parasites, and infection status for vector-borne microparasites. We then used regression trees to test if variation in immune indices could be explained by among-site differences (parasite pressure), among-individual differences in infestation intensity and infection status (parasite load), or other intrinsic factors. Regression trees revealed splits among sites for haptoglobin, hemagglutination, and body-mass corrected spleen size. We also found splits based on infection/infestation for haptoglobin, hemolysis, and neutrophil to lymphocyte ratio. Furthermore, we found a split between species for hemolysis and splits based on body mass for haptoglobin, hemagglutination, hematocrit, and body-mass corrected spleen size. Our results suggest that both parasite pressure and parasite load influence the immune system of wild rodents. Additional studies linking disease ecology and ecological immunology are needed to understand better the complexities of host–parasite interactions and how these interactions shape zoonotic disease risk.

    Impact of vertebrate communities on Ixodes ricinus-borne disease risk in forest areas
    Takumi, Katsuhisa ; Sprong, Hein ; Hofmeester, Tim R. - \ 2019
    Parasites & Vectors 12 (2019)1. - ISSN 1756-3305
    Anaplasma phagocytophilum - Borrelia burgdorferi (s.l.) - Borrelia miyamotoi - Ixodes ricinus - Lyme borreliosis - Neoehrlichia mikurensis - Transmission dynamics - Vector-borne disease

    Background: The density of questing ticks infected with tick-borne pathogens is an important parameter that determines tick-borne disease risk. An important factor determining this density is the availability of different wildlife species as hosts for ticks and their pathogens. Here, we investigated how wildlife communities contribute to tick-borne disease risk. The density of Ixodes ricinus nymphs infected with Borrelia burgdorferi (sensu lato), Borrelia miyamotoi, Neoehrlichia mikurensis and Anaplasma phagocytophilum among 19 forest sites were correlated to the encounter probability of different vertebrate hosts, determined by encounter rates as measured by (camera) trapping and mathematical modeling. Result: We found that the density of any tick life stage was proportional to the encounter probability of ungulates. Moreover, the density of nymphs decreased with the encounter probability of hare, rabbit and red fox. The density of nymphs infected with the transovarially-transmitted B. miyamotoi increased with the density of questing nymphs and the encounter probability of bank vole. The density of nymphs infected with all other pathogens increased with the encounter probability of competent hosts: bank vole for Borrelia afzelii and N. mikurensis, ungulates for A. phagocytophilum and blackbird for Borrelia garinii and Borrelia valaisiana. The negative relationship we found was a decrease in the density of nymphs infected with B. garinii and B. valaisiana with the encounter probability of wood mouse. Conclusions: Only a few animal species drive the densities of infected nymphs in forested areas. There, foxes and leporids have negative effects on tick abundance, and consequently on the density of infected nymphs. The abundance of competent hosts generally drives the abundances of their tick-borne pathogen. A dilution effect was only observed for bird-associated Lyme spirochetes.[Figure not available: see fulltext.]

    Temporal-Spatial Variation in Questing Tick Activity in the Netherlands: The Effect of Climatic and Habitat Factors
    Hartemink, Nienke ; Vliet, Arnold Van; Sprong, Hein ; Jacobs, Frans ; Garcia-Martí, Irene ; Zurita-Milla, Raul ; Takken, Willem - \ 2019
    Vector-Borne and Zoonotic Diseases 19 (2019)7. - ISSN 1530-3667 - p. 494 - 505.
    Ixodes ricinus - phenology - population dynamics - saturation deficit - soil structure - temperature - vegetation

    Longitudinal studies are fundamental in the assessment of the effect of environmental factors on tick population dynamics. In this study, we use data from a 10-year study in 11 different locations in the Netherlands to gauge the effects of climatic and habitat factors on the temporal and spatial variation in questing tick activity. Marked differences in the total number of ticks were found between locations and between years. We investigated which climatic and habitat factors might explain this variation. No effects of climatic factors on the total number of ticks per year were observed, but we found a clear effect of temperature on the onset of tick activity. In addition, we found positive associations between (1) humus layer thickness and densities of all three stages, (2) moss and blackberry abundance and larval densities, and (3) blueberry abundance and densities of larva and nymphs. We conclude that climatic variables do not have a straightforward association with tick density in the Netherlands, but that winter and spring temperatures influence the onset of tick activity. Habitats with apparently similar vegetation types can still differ in tick population densities, indicating that local composition of vegetation and especially of wildlife is likely to contribute considerably to the spatial variation in tick densities.

    Anaplasma phagocytophilum evolves in geographical and biotic niches of vertebrates and ticks
    Jaarsma, Ryanne I. ; Sprong, Hein ; Takumi, Katsuhisa ; Kazimirova, Maria ; Silaghi, Cornelia ; Mysterud, Atle ; Rudolf, Ivo ; Beck, Relja ; Földvári, Gábor ; Tomassone, Laura ; Groenevelt, Margit ; Everts, Reinard R. ; Rijks, Jolianne M. ; Ecke, Frauke ; Hörnfeldt, Birger ; Modrý, David ; Majerová, Karolina ; Votýpka, Jan ; Estrada-Peña, Agustín - \ 2019
    Parasites & Vectors 12 (2019). - ISSN 1756-3305
    Anaplasma phagocytophilum - Ixodidae - Molecular epidemiology - Network analysis - Ticks - Transmission dynamics

    Background: Anaplasma phagocytophilum is currently regarded as a single species. However, molecular studies indicate that it can be subdivided into ecotypes, each with distinct but overlapping transmission cycle. Here, we evaluate the interactions between and within clusters of haplotypes of the bacterium isolated from vertebrates and ticks, using phylogenetic and network-based methods. Methods: The presence of A. phagocytophilum DNA was determined in ticks and vertebrate tissue samples. A fragment of the groEl gene was amplified and sequenced from qPCR-positive lysates. Additional groEl sequences from ticks and vertebrate reservoirs were obtained from GenBank and through literature searches, resulting in a dataset consisting of 1623 A. phagocytophilum field isolates. Phylogenetic analyses were used to infer clusters of haplotypes and to assess phylogenetic clustering of A. phagocytophilum in vertebrates or ticks. Network-based methods were used to resolve host-vector interactions and their relative importance in the segregating communities of haplotypes. Results: Phylogenetic analyses resulted in 199 haplotypes within eight network-derived clusters, which were allocated to four ecotypes. The interactions of haplotypes between ticks, vertebrates and geographical origin, were visualized and quantified from networks. A high number of haplotypes were recorded in the tick Ixodes ricinus. Communities of A. phagocytophilum recorded from Korea, Japan, Far Eastern Russia, as well as those associated with rodents had no links with the larger set of isolates associated with I. ricinus, suggesting different evolutionary pressures. Rodents appeared to have a range of haplotypes associated with either Ixodes trianguliceps or Ixodes persulcatus and Ixodes pavlovskyi. Haplotypes found in rodents in Russia had low similarities with those recorded in rodents in other regions and shaped separate communities. Conclusions: The groEl gene fragment of A. phagocytophilum provides information about spatial segregation and associations of haplotypes to particular vector-host interactions. Further research is needed to understand the circulation of this bacterium in the gap between Europe and Asia before the overview of the speciation features of this bacterium is complete. Environmental traits may also play a role in the evolution of A. phagocytophilum in ecotypes through yet unknown relationships.

    Risk factors associated with sustained circulation of six zoonotic arboviruses: A systematic review for selection of surveillance sites in non-endemic areas
    Esser, Helen J. ; Mögling, Ramona ; Cleton, Natalie B. ; Jeugd, Henk Van Der; Sprong, Hein ; Stroo, Arjan ; Koopmans, Marion P.G. ; Boer, Willem F. De; Reusken, Chantal B.E.M. - \ 2019
    Parasites & Vectors 12 (2019)1. - ISSN 1756-3305
    Crimean-Congo hemorrhagic fever virus - Japanese encephalitis virus - Louping-ill virus - Rift Valley fever virus - Tick-borne encephalitis virus - West Nile virus

    Arboviruses represent a significant burden to public health and local economies due to their ability to cause unpredictable and widespread epidemics. To maximize early detection of arbovirus emergence in non-endemic areas, surveillance efforts should target areas where circulation is most likely. However, identifying such hotspots of potential emergence is a major challenge. The ecological conditions leading to arbovirus outbreaks are shaped by complex interactions between the virus, its vertebrate hosts, arthropod vector, and abiotic environment that are often poorly understood. Here, we systematically review the ecological risk factors associated with the circulation of six arboviruses that are of considerable concern to northwestern Europe. These include three mosquito-borne viruses (Japanese encephalitis virus, West Nile virus, Rift Valley fever virus) and three tick-borne viruses (Crimean-Congo hemorrhagic fever virus, tick-borne encephalitis virus, and louping-ill virus). We consider both intrinsic (e.g. vector and reservoir host competence) and extrinsic (e.g. temperature, precipitation, host densities, land use) risk factors, identify current knowledge gaps, and discuss future directions. Our systematic review provides baseline information for the identification of regions and habitats that have suitable ecological conditions for endemic circulation, and therefore may be used to target early warning surveillance programs aimed at detecting multi-virus and/or arbovirus emergence.

    Selecting mixtures on the basis of dietary exposure and hazard data : application to pesticide exposure in the European population in relation to steatosis
    Crépet, Amélie ; Vanacker, Marie ; Sprong, Corinne ; Boer, Waldo de; Blaznik, Urska ; Kennedy, Marc ; Anagnostopoulos, Chris ; Christodoulou, Despo Louca ; Ruprich, Jiří ; Rehurkova, Irena ; Domingo, José Luis ; Hamborg Jensen, Bodil ; Metruccio, Francesca ; Moretto, Angelo ; Jacxsens, Liesbeth ; Spanoghe, Pieter ; Senaeve, David ; Voet, Hilko van der; Klaveren, Jacob van - \ 2019
    International Journal of Hygiene and Environmental Health 222 (2019)2. - ISSN 1438-4639 - p. 291 - 306.
    Cumulative assessment group - Dietary exposure and hazard - Mixture prioritisation - Relative potency factors - Sparse non-negative matrix underestimation

    Populations are exposed to mixtures of pesticides through their diet on a daily basis. The question of which substances should be assessed together remains a major challenge due to the complexity of the mixtures. In addition, the associated risk is difficult to characterise. The EuroMix project (European Test and Risk Assessment Strategies for Mixtures) has developed a strategy for mixture risk assessment. In particular, it has proposed a methodology that combines exposures and hazard information to identify relevant mixtures of chemicals belonging to any cumulative assessment group (CAG) to which the European population is exposed via food. For the purposes of this study, food consumption and pesticide residue data in food and drinking water were obtained from national surveys in nine European countries. Mixtures of pesticides were identified by a sparse non-negative matrix underestimation (SNMU) applied to the specific liver steatosis effect in children from 11 to 15 years of age, and in adults from 18 to 64 years of age in nine European countries. Exposures and mixtures of 144 pesticides were evaluated through four different scenarios: (1) chronic exposure with a merged concentration dataset in the adult population, (2) chronic exposure with country-specific concentration datasets in the adult population, (3) acute exposure with a merged concentration dataset in the adult population, and (4) chronic exposure with a merged concentration dataset in the paediatric population. The relative potency factors of each substance were calculated to express their potency relative to flusilazole, which was chosen as the reference compound. The selection of mixtures and the evaluation of exposures for each country were carried out using the Monte Carlo Risk Assessment (MCRA) software. Concerning chronic exposure, one mixture explained the largest proportion of the total variance for each country, while in acute exposure, several mixtures were often involved. The results showed that there were 15 main pesticides in the mixtures, with a high contribution of imazalil and dithiocarbamate. Since the concentrations provided by the different countries were merged in the scenario using merged concentration data, differences between countries result from differences in food consumption behaviours. These results support the approach that using merged concentration data to estimate exposures in Europe seems to be realistic, as foods are traded across European borders. The originality of the proposed approach was to start from a CAG and to integrate information from combined exposures to identify a refined list of mixtures with fewer components. As this approach was sensitive to the input data and required significant resources, efforts should continue regarding data collection and harmonisation among the different aspects within the pesticides regulatory framework, and to develop methods to group substances and mixtures to characterise the risk.

    Prevalence of tick-borne viruses in Ixodes ricinus assessed by high-throughput real-time PCR
    Gondard, Mathilde ; Michelet, Lorraine ; Nisavanh, Athinna ; Devillers, Elodie ; Delannoy, Sabine ; Fach, Patrick ; Aspan, Anna ; Ullman, Karin ; Chirico, Jan ; Hoffmann, Bernd ; Wal, Fimme Jan van der; Koeijer, Aline de; Solt-Smits, Conny van; Jahfari, Seta ; Sprong, Hein ; Mansfield, Karen L. ; Fooks, Anthony R. ; Klitgaard, Kirstine ; Bødker, Rene ; Moutailler, Sara - \ 2018
    Pathogens and Disease 76 (2018)8. - ISSN 2049-632X
    Europe - microfluidic analysis - molecular epidemiology - surveillance - tick borne viruses

    Ticks are one of the principal arthropod vectors of human and animal infectious diseases. Whereas the prevalence of tick-borne encephalitis virus in ticks in Europe is well studied, there is less information available on the prevalence of the other tick-borne viruses (TBVs) existing worldwide. The aim of this study was to improve the epidemiological survey tools of TBVs by the development of an efficient high-throughput test to screen a wide range of viruses in ticks. In this study, we developed a new high-throughput virus-detection assay based on parallel real-time PCRs on a microfluidic system, and used it to perform a large scale epidemiological survey screening for the presence of 21 TBVs in 18 135 nymphs of Ixodes ricinus collected from five European countries. This extensive investigation has (i) evaluated the prevalence of four viruses present in the collected ticks, (ii) allowed the identification of viruses in regions where they were previously undetected. In conclusion, we have demonstrated the capabilities of this new screening method that allows the detection of numerous TBVs in a large number of ticks. This tool represents a powerful and rapid system for TBVs surveillance in Europe and could be easily customized to assess viral emergence.

    The genetic diversity of Borrelia afzelii is not maintained by the diversity of the rodent hosts
    Coipan, Claudia E. ; Duijvendijk, L.A.G. van; Hofmeester, T.R. ; Takumi, Katsuhisa ; Sprong, H. - \ 2018
    Borrelia burgdorferi - Ixodes ricinus larvae - rodents - IGS - ospC - dbpA
    Background Small mammals are essential in the enzootic cycle of many tick-borne pathogens (TBP). To understand their contribution to the genetic diversity of Borrelia afzelii, the most prevalent TBP in questing Ixodes ricinus, we compared the genetic variants of B. afzelii at three distinct genetic loci. We chose two plasmid loci, dbpA and ospC, and a chromosomal one, IGS. Results While the larvae that fed on shrews (Sorex sp.) tested negative for B. afzelii, those fed on bank voles (Myodes glareolus) and wood mice (Apodemus sylvaticus) showed high infection prevalences of 0.13 and 0.27, respectively. Despite the high genetic diversity within B. afzelii, there was no difference between wood mice and bank voles in the number and types of B. afzelii haplotypes they transmit. Conclusions The genetic diversity in B. afzelii cannot be explained by separate enzootic cycles in wood mice and bank voles.
    Role of mustelids in the life-cycle of ixodid ticks and transmission cycles of four tick-borne pathogens
    Hofmeester, Tim R. ; Krawczyk, Aleksandra I. ; Docters van Leeuwen, Arieke ; Fonville, Manoj ; Montizaan, Margriet G.E. ; Berge, Koen van den; Gouwy, Jan ; Ruyts, Sanne C. ; Verheyen, Kris ; Sprong, Hein - \ 2018
    Parasites & Vectors 11 (2018)1. - ISSN 1756-3305 - 13 p.
    Anaplasma phagocytophilum - Borrelia burgdorferi (s.l.) - Borrelia miyamotoi - Ixodes hexagonus - Ixodes ricinus - Martes foina - Martes martes - Meles meles - Mustela putorius - Neoehrlichia mikurensis

    BACKGROUND: Elucidating which wildlife species significantly contribute to the maintenance of Ixodes ricinus populations and the enzootic cycles of the pathogens they transmit is imperative in understanding the driving forces behind the emergence of tick-borne diseases. Here, we aimed to quantify the relative contribution of four mustelid species in the life-cycles of I. ricinus and Borrelia burgdorferi (sensu lato) in forested areas and to investigate their role in the transmission of other tick-borne pathogens. Road-killed badgers, pine martens, stone martens and polecats were collected in Belgium and the Netherlands. Their organs and feeding ticks were tested for the presence of tick-borne pathogens. RESULTS: Ixodes hexagonus and I. ricinus were found on half of the screened animals (n = 637). Pine martens had the highest I. ricinus burden, whereas polecats had the highest I. hexagonus burden. We detected DNA from B. burgdorferi (s.l.) and Anaplasma phagocytophilum in organs of all four mustelid species (n = 789), and Neoehrlichia mikurensis DNA was detected in all species, except badgers. DNA from B. miyamotoi was not detected in any of the investigated mustelids. From the 15 larvae of I. ricinus feeding on pine martens (n = 44), only one was positive for B. miyamotoi DNA, and all tested negative for B. burgdorferi (s.l.), N. mikurensis and A. phagocytophilum. The two feeding larvae from the investigated polecats (n = 364) and stone martens (n = 39) were negative for all four pathogens. The infection rate of N. mikurensis was higher in feeding nymphs collected from mustelids compared to questing nymphs, but not for B. burgdorferi (s.l.), B. miyamotoi or A. phagocytophilum. CONCLUSIONS: Although all stages of I. ricinus can be found on badgers, polecats, pine and stone martens, their relative contribution to the life-cycle of I. ricinus in forested areas is less than 1%. Consequently, the relative contribution of mustelids to the enzootic cycles of I. ricinus-borne pathogens is negligible, despite the presence of these pathogens in organs and feeding ticks. Interestingly, all four mustelid species carried all stages of I. hexagonus, potentially maintaining enzootic cycles of this tick species apart from the cycle involving hedgehogs as main host species.

    The genetic diversity of Borrelia afzelii is not maintained by the diversity of the rodent hosts
    Coipan, Claudia E. ; Duijvendijk, Gilian L.A. van; Hofmeester, Tim R. ; Takumi, Katsuhisa ; Sprong, Hein - \ 2018
    Parasites & Vectors 11 (2018)1. - ISSN 1756-3305
    Borrelia burgdorferi (s.l.) - dbpA - IGS - Ixodes ricinus larvae - ospC - Rodents

    Background: Small mammals are essential in the enzootic cycle of many tick-borne pathogens (TBP). To understand their contribution to the genetic diversity of Borrelia afzelii, the most prevalent TBP in questing Ixodes ricinus, we compared the genetic variants of B. afzelii at three distinct genetic loci. We chose two plasmid loci, dbpA and ospC, and a chromosomal one, IGS. Results: While the larvae that fed on shrews (Sorex sp.) tested negative for B. afzelii, those fed on bank voles (Myodes glareolus) and wood mice (Apodemus sylvaticus) showed high infection prevalences of 0.13 and 0.27, respectively. Despite the high genetic diversity within B. afzelii, there was no difference between wood mice and bank voles in the number and types of B. afzelii haplotypes they transmit. Conclusions: The genetic diversity in B. afzelii cannot be explained by separate enzootic cycles in wood mice and bank voles.

    Low probability of a dilution effect for Lyme borreliosis in Belgian forests
    Ruyts, Sanne C. ; Landuyt, Dries ; Ampoorter, Evy ; Heylen, Dieter ; Ehrmann, Steffen ; Coipan, Elena C. ; Matthysen, Erik ; Sprong, Hein ; Verheyen, Kris - \ 2018
    Ticks and Tick-borne Diseases 9 (2018)5. - ISSN 1877-959X - p. 1143 - 1152.
    Bayesian belief network - Biodiversity - Borrelia afzelii - Ixodes ricinus - Tick - Vector-borne disease
    An increasing number of studies have investigated the consequences of biodiversity loss for the occurrence of vector-borne diseases such as Lyme borreliosis, the most common tick-borne disease in the northern hemisphere. As host species differ in their ability to transmit the Lyme borreliosis bacteria Borrelia burgdorferi s.l. to ticks, increased host diversity can decrease disease prevalence by increasing the proportion of dilution hosts, host species that transmit pathogens less efficiently. Previous research shows that Lyme borreliosis risk differs between forest types and suggests that a higher diversity of host species might dilute the contribution of small rodents to infect ticks with B. afzelii, a common Borrelia genospecies. However, empirical evidence for a dilution effect in Europe is largely lacking. We tested the dilution effect hypothesis in 19 Belgian forest stands of different forest types along a diversity gradient. We used empirical data and a Bayesian belief network to investigate the impact of the proportion of dilution hosts on the density of ticks infected with B. afzelii, and identified the key drivers determining the density of infected ticks, which is a measure of human infection risk. Densities of ticks and B. afzelii infection prevalence differed between forest types, but the model indicated that the density of infected ticks is hardly affected by dilution. The most important variables explaining variability in disease risk were related to the density of ticks. Combining empirical data with a model-based approach supported decision making to reduce tick-borne disease risk. We found a low probability of a dilution effect for Lyme borreliosis in a north-western European context. We emphasize that under these circumstances, Lyme borreliosis prevention should rather aim at reducing tick-human contact rate instead of attempting to increase the proportion of dilution hosts.
    Control of Lyme borreliosis and other Ixodes ricinus-borne diseases
    Sprong, Hein ; Azagi, Tal ; Hoornstra, Dieuwertje ; Nijhof, Ard M. ; Knorr, Sarah ; Baarsma, M.E. ; Hovius, Joppe W. - \ 2018
    Parasites & Vectors 11 (2018)1. - ISSN 1756-3305
    Anaplasmosis - Ixodes ricinus - Lyme borreliosis - Prevention - Tick-borne encephalitis - Transmission cycles - Vaccines
    Lyme borreliosis (LB) and other Ixodes ricinus-borne diseases (TBDs) are diseases that emerge from interactions of humans and domestic animals with infected ticks in nature. Nature, environmental and health policies at (inter)national and local levels affect the risk, disease burden and costs of TBDs. Knowledge on ticks, their pathogens and the diseases they cause have been increasing, and resulted in the discovery of a diversity of control options, which often are not highly effective on their own. Control strategies involving concerted actions from human and animal health sectors as well as from nature managers have not been formulated, let alone implemented. Control of TBDs asks for a "health in all policies" approach, both at the (inter)national level, but also at local levels. For example, wildlife protection and creating urban green spaces are important for animal and human well-being, but may increase the risk of TBDs. In contrast, culling or fencing out deer decreases the risk for TBDs under specific conditions, but may have adverse effects on biodiversity or may be societally unacceptable. Therefore, in the end, nature and health workers together must carry out tailor-made control options for the control of TBDs for humans and animals, with minimal effects on the environment. In that regard, multidisciplinary approaches in environmental, but also medical settings are needed. To facilitate this, communication and collaboration between experts from different fields, which may include patient representatives, should be promoted.
    Year-to-year variation in the density of Ixodes ricinus ticks and the prevalence of the rodent-associated human pathogens Borrelia afzelii and B. miyamotoi in different forest types
    Ruyts, Sanne C. ; Tack, Wesley ; Ampoorter, Evy ; Coipan, Elena C. ; Matthysen, Erik ; Heylen, Dieter ; Sprong, Hein ; Verheyen, Kris - \ 2018
    Ticks and Tick-borne Diseases 9 (2018)2. - ISSN 1877-959X - p. 141 - 145.
    Host community - Lyme borreliosis - Mast year - Spatiotemporal dynamics - Tick-borne disease risk

    The human pathogens Borrelia afzelii, which causes Lyme borreliosis and B. miyamotoi, which causes relapsing fever, both circulate between Ixodes ricinus ticks and rodents. The spatiotemporal dynamics in the prevalence of these pathogens have not yet been fully elucidated, but probably depend on the spatiotemporal population dynamics of small rodents. We aimed to evaluate the effect of different forest types on the density of infected nymphs in different years and to obtain more knowledge about the spatial and temporal patterns of ticks and tick-borne pathogens. We analysed unfed nymphal ticks from 22 stands of four different forest types in Belgium in 2009, 2010, 2013 and 2014 and found that the density of nymphs in general and the density of nymphs infected with B. afzelii and B. miyamotoi varied yearly, but without temporal variation in the infection prevalence. The yearly variation in density of infected nymphs in our study thus seems to be caused most by the variation in the density of nymphs, which makes it a good predictor of disease risk. The risk for rodent-associated tick-borne diseases also varied between forest types. We stress the need to elucidate the contribution of the host community composition to tick-borne disease risk.

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