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.

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On the role of vaccine dose and antigenic distance in the transmission dynamics of Highly Pathogenic Avian Influenza (HPAI) H5N1 virus and its selected mutants in vaccinated animals
Sitaras, Ioannis - \ 2017
Wageningen University. Promotor(en): Mart de Jong, co-promotor(en): Ben Peeters. - Wageningen : Wageningen University - ISBN 9789463438063 - 209
avian influenza viruses - avian influenza - disease transmission - vaccines - vaccination - dosage - antigenic variation - mutants - mutations - immunity - vaccine development - virology - epidemiology - aviaire influenzavirussen - aviaire influenza - ziekteoverdracht - vaccins - vaccinatie - dosering - antigene variatie - mutanten - mutaties - immuniteit - vaccinontwikkeling - virologie - epidemiologie

Influenza virus infections can cause high morbidity and mortality rates among animals and humans, and result in staggering direct and indirect financial losses amounting to billions of US dollars. Ever since it emerged in 1996 in Guangdong province, People’s Republic of China, one particular highly pathogenic avian influenza (HPAI) H5N1 virus has spread globally, and is responsible for massive losses of poultry, as well as human infections. For these reasons, HPAI H5N1 is considered as one of the viruses possible to cause a future influenza pandemic.

One of the main reasons why influenza is a recurring problem is its ability to constantly evolve through the selection of mutants that are able to avoid immunity (be it natural or acquired). Due to the accumulation of mutations during genome replication, diverse/variant influenza genome sequences co-exist in a virus pool (quasispecies). These sequences can contain mutations that are able to confer selective advantages to the influenza virus given the opportunity. As a consequence, whenever a situation arises that places the virus under any type of pressure that the dominant virus sequence cannot cope with (i.e. immune pressure, selective receptor binding, etc.), the virus with the genome sequence that allows it to better adapt to that particular pressure becomes selected and takes over.

Because of the influenza virus’s high rate of mutations, a global surveillance network is in place to monitor changes in circulating strains among humans that would warrant an update of the vaccines used. For human influenza strains, vaccines are updated frequently (every one or two years) and a similar situation holds true for racehorse vaccination. For avian influenza vaccination, however, the situation is different. In most countries, vaccination against avian influenza is not used, and in the countries where vaccines are used (either as routine or emergency measures), they are not updated as frequently as human vaccines are. In addition, in many instances vaccination against avian influenza viruses has met with some spectacular failures, since it failed to produce a level of immunity that would protect against circulating field strains. These vaccination failures have often been attributed to the fact that without constant vaccine updating (as is done for human influenza), the vaccines used are not able to keep up with continuously evolving antigenic variants selected in the field, and thus to protect poultry against them. In addition, since it is known that immune pressure resulting from vaccination can be a driving force in the evolution of influenza viruses and the selection of immune-escape mutants, there is a school of thought that posits that vaccination against avian influenza is not only a very expensive affair (especially if vaccines need to be frequently updated), but can also lead to selection of mutants that are able to avoid vaccination-induced immunity.

The research reported in this thesis started with addressing the gaps in the knowledge regarding the role of vaccination-induced immunity in the selection of immune-escape mutants of HPAI H5N1, and if there is a way for vaccines to still be able to protect against antigenically-distant variants of the vaccine seed strain, without the need for frequent vaccine updates.

Our first step in studying influenza virus evolution and selection of immune-escape mutants was to investigate how antigenic pressure may drive the selection of such mutants, and what the effect of the selected mutations on the pathogenicity and transmissibility of the mutants may be. Although there exist a variety of methods to select for influenza virus mutations (i.e. monoclonal antibodies, site-directed mutagenesis, reverse genetics, etc.), none of them is representative of selection as it happens in a vaccinated animal. In Chapter 2, we discuss in detail a laboratory-based system we have developed, in which immune-escape mutants are selected using homologous polyclonal chicken sera, similar to how they are selected in the field due to vaccination- induced immune pressure. We find that selection takes place early on, and additional mutations are selected when immune pressure is increased. Antigenic distances between the selected mutants and their parent strains are also increased throughout the selection process, but not in a linear fashion. Our selection system proved to be robust and replicable, and to be representative of selection in the field, since the mutations we selected for are also found in naturally-selected field isolates, and the antigenic distances between our selected mutants and their parent strains are similar to antigenic distances between vaccine strains and field isolates.

We continued our research by addressing the roles played by vaccine dose (and resulting immunity) and antigenic distance between vaccine and challenge strains, in the transmission of HPAI H5N1 viruses, by employing transmission experiments using vaccinated chickens (Chapter 3). To our surprise, we found that the effect of antigenic distances between vaccine and challenge strains on transmission is very small compared to the effect of vaccine dose. We then quantified, for the first time, the minimum level of immunity and minimum percentage of the vaccinated population exhibiting said immunity, in order for vaccines to be able to protect against transmission even of strains that are antigenically distant to the vaccine seed strain. Transmission of such strains in well-vaccinated populations would allow for a scenario where vaccination- induced immunity may drive the selection of immune-escape mutants. Our results show that in order for vaccines to prevent transmission of antigenically distant strains (such as the ones resulting from selection due to immune pressure), the threshold level of immunity against these strains should be ≥23 haemagglutination inhibition units (HIU), in at least 86.5% of the vaccinated population. This level of immunity can be estimated by knowing the antigenic distance between the vaccine and challenge (field) strain, and the HI titre against the vaccine strain, which would then allow the approximate level of immunity against the field strain to be deduced. For example, assuming the HI titre against a vaccine strain is 210 HIU, and the distance with the challenge (field) strain is 24 HIU, according to our results the vaccine should be able to protect against the challenge strain, because the difference in HI titres should be around 26 HIU (i.e. above 23 HIU). These results, taken together with our previous work on selection of mutants, where we showed that the antigenic distances between our mutants and their parent strains are representative of distances found in the field, point to the fact that it is unlikely that vaccination-induced immunity can lead to selection of mutants able to escape it, given that a threshold level of immunity in a minimum percentage of the vaccinated population is achieved. As a consequence, we believe that constant vaccine updating may not be necessary for avian influenza viruses, as long as a threshold level of immunity is maintained. This makes vaccination a more attractive control measure, both from a health perspective and a financial one, than just applying biosecurity measures.

To examine the effect the mutations in the haemagglutinin protein of our selected mutants may have in their transmission among chickens vaccinated with the parent strain, we used reverse genetics techniques to insert the HA gene of our most antigenically distant mutant into the parent strain backbone (Chapter 4). We vaccinated animals with a sub-optimal dose of vaccine, and we concluded that the mutations we selected for did not allow the mutant to avoid even low levels of immunity, such as the ones resulting from a sub-optimal vaccine dose (which resembles a poor field vaccination scenario). At the same time, the HA mutations we selected for did not appear to have a negative effect either on the pathogenicity of the mutant, or its ability to transmit to unvaccinated animals, since both parameters were comparable to the parent strain.

Finally, we studied the role inter-animal variation in immunity – as measured by HI titres – has in the accuracy of antigenic cartography calculations (Chapter 5). We found that using sera from more than one animal significantly increased the accuracy of antigenic distance calculations, since it takes into account individual differences in immune responses to vaccination, an inevitable phenomenon documented in both humans and animals. In addition, we increased the accuracy of antigenic maps by avoiding the use of dimension-reducing algorithms as is currently done. By not reducing the dimensionality of virus positioning in space, our maps retain the original geometry between strains or sera, leading to more accurate positioning (Chapters 2 and 5). We hope that improving the accuracy of antigenic cartography can lead to a more precise surveillance of influenza evolution and better informed decisions regarding the need to update vaccines.

Taken collectively, our results can improve field vaccination outcomes, since they provide guidelines on how to increase vaccination efficiency in stopping transmission of even antigenically-distant strains. In addition, our method for selecting for immune- escape mutants can be a valuable addition to research on influenza virus evolution. Moreover, policy making decisions regarding vaccination against any type of influenza can also benefit from our improvement on antigenic cartography accuracy, saving unnecessary costs in vaccine updating, and reducing morbidity and mortality of both animals and humans.

Eco-epidemiology of Bovine Tuberculosis (bTB) in an African savanna : The conflict between traditional pastoralist adaptations and disease transmission in the modern era
Dejene, Sintayehu Workeneh - \ 2017
Wageningen University. Promotor(en): Herbert Prins, co-promotor(en): Fred de Boer; Ignas Heitkonig. - Wageningen : Wageningen University - ISBN 9789463436588 - 119
cattle diseases - tuberculosis - disease transmission - pastoralism - animal ecology - risk factors - ethiopia - rundveeziekten - tuberculose - ziekteoverdracht - pastoralisme - dierecologie - risicofactoren - ethiopië

Bovine tuberculosis (bTB) is a zoonotic disease, and remains a cause of concern for livestock, wildlife and human health, especially in Ethiopia. It is a contagious disease, so close contact between animals or sharing of feed between infected and non-infected animals are major risk factors for transmission. Thus, improving the understanding of the factors that promote contact between hosts (i.e., livestock animals but also wild ruminants) is critical for limiting bTB transmission in pastoral, multi-host communities. I found that the older the age of the cattle and the lower the body condition, the higher the chance of a positive bTB test result at the individual animal level. Moreover, at herd level, herd size, contact with wildlife, and the interaction of herd size and contact with wildlife were identified as significant risk factors for bTB prevalence in cattle in Ethiopia. Further to what is already known from the past studies, I found that the probability of contact with wildlife was positively influenced by herd size, through herd movement. As larger herds moved more and grazed in larger areas, the probability of grazing in an area with wildlife and contact with either infected cattle or infected wildlife hosts increased; this also increased the chances for bTB infection. I detected a possible ‘dilution effect’ in bTB, where a higher evenness of mammal species reduced the probability of bTB occurrence. This dilution effect might be caused by encounter reduction. Because the encounter rate is proportional to the distribution of the host species; evenness would then capture the probability of encounter between pathogens and each host species. Thus, species evenness can be an appropriate measure of biodiversity to explain disease risk. I also showed that bTB prevalence was positively associated with the invasion of the plant Prosopis (Prosopis juliflora), maybe due to the loss in host species evenness and the increase in cattle movement as a consequence of the loss of palatable grasses in Prosopis-infested areas. Moreover, social contacts between herd owners are also important, as I found that herds with a greater number of edges in a (social) network had more connections in the livestock transfer network, increasing the probability of becoming infected with bTB. Thus, cultural components like large herd size and social contacts are at odds with the global One Health rationale to reduce bTB.

The role of Culex pipiens mosquitoes in transmission of West Nile virus in Europe
Vogels, Chantal B.F. - \ 2017
Wageningen University. Promotor(en): Marcel Dicke, co-promotor(en): Sander Koenraadt. - Wageningen : Wageningen University - ISBN 9789463436151 - 211
culex pipiens - mosquito-borne diseases - west nile virus - disease transmission - disease vectors - vector-borne diseases - europe - ziekten overgebracht door muskieten - west-nijlvirus - ziekteoverdracht - vectoren, ziekten - ziekten overgebracht door vectoren - europa

West Nile virus (WNV) is maintained in a natural transmission cycle between mosquito vectors and bird hosts. However, mosquitoes can also transmit WNV to mammals, such as humans and horses, which may result in disease. In Europe, such cases of WNV disease are yearly recurring in southern and central Europe, but have not been detected in northern Europe. The absence of WNV outbreaks in northern Europe may be explained by lowered vector competence of the main vector for WNV: the northern house mosquito, Culex (Cx.) pipiens. The aim of this thesis was, therefore, to investigate the role of Cx. pipiens mosquitoes in transmission of WNV in Europe, in order to understand differences in WNV circulation between northern and southern Europe.

The species Cx. pipiens consists of two biotypes, pipiens and molestus, which can form hybrids. Both biotypes and their hybrids are morphologically identical but differ in their behaviour, which may have consequences for WNV transmission. In this thesis, the Cx. pipiens biotype composition was investigated in The Netherlands, and more broadly at the European scale. These studies revealed that both biotypes and their hybrids are present throughout The Netherlands, and that there is a shift towards relatively more biotype pipiens mosquitoes at northern latitudes in Europe. The next step was to assess vector competence of these northern European biotypes and their hybrids, and to make a direct comparison with vector competence of a southern European population. Both biotypes and their hybrids originating from The Netherlands are competent vectors for WNV. Interestingly, no differences in vector competence were found between a Dutch and Italian biotype pipiens population. However, both studies revealed that low temperatures of 18 °C are an important limiting factor for WNV transmission. A more in-depth study on the effects of WNV on the host-seeking behaviour of biotype pipiens mosquitoes revealed that WNV infection reduces the host-seeking response towards host odour, but that other fitness parameters (e.g. flight activity, blood-feeding, and survival) are not affected. When results from the biotype composition and vector competence studies were included in a newly developed R0 model, it becomes clear that biotype pipiens is the main contributor to WNV transmission.

The results presented in this thesis show that the Cx. pipiens biotypes and their hybrids are present throughout The Netherlands, and that they can transmit WNV under favourable climatic conditions. The absence of WNV outbreaks in northern Europe can most likely be explained by low temperature which has a negative effect on mosquito abundance, vector competence, and the duration of the infectious period. When considering the outcomes of this thesis in the light of climate change, northern European countries such as The Netherlands should be prepared for future WNV transmission.

Plantenvirussen in het vizier
Stijger, I. ; Verbeek, M. - \ 2016
Wageningen UR
plantenvirussen - virusziekten - ziekteoverdracht - detectie - ziektedistributie - diagnose - bedrijfshygiëne - plant viruses - viral diseases - disease transmission - detection - disease distribution - diagnosis - industrial hygiene
Aandacht wordt geschonken aan: voedingswater, micro-leven, rasverschillen, en oud stekmateriaal. Poster van PlantgezondheidEvent 12 maart 2015.
Transmission of antibiotic resistance from animals to humans : Broilers as a reservoir of ESBL-producing bacteria
Huijbers, P.M.C. - \ 2016
Wageningen University. Promotor(en): Mart de Jong; Lisette Graat; E. van Duijkeren. - Wageningen : Wageningen University - ISBN 9789462576216 - 156 p.
broilers - man - disease transmission - antibiotic resistance - bacteria - enterobacteriaceae - poultry farming - epidemiology - vleeskuikens - mens - ziekteoverdracht - antibioticaresistentie - bacteriën - pluimveehouderij - epidemiologie

Huijbers, P.M.C. (2016). Transmission of antibiotic resistance from animals to humans: Broilers as a reservoir of ESBL-producing bacteria. PhD thesis, Wageningen University, Wageningen, the Netherlands.

Antibiotic resistance in animals becomes a public health issue when there is transmission of antibiotic resistant bacteria, or their resistance genes, from animals to humans. β-lactam antibiotics are critically important for the treatment of human bacterial infections. Resistance to this class of antibiotics, mediated by extended-spectrum β-lactamases (ESBL) has emerged. Broilers might contribute to transmission to humans due to the high prevalence of ESBL-producing Enterobacteriaceae among their intestinal biome, compared to other livestock species, companion animals, and wildlife. Transmission to humans might occur via the food chain, by direct contact or via the environment. The aim was to investigate transmission of antibiotic resistant bacteria between animals and humans, and more specifically transmission of ESBL-producing E. coli between broilers, and between broilers and humans in varying degrees of contact with these animals. Systematically collected and categorised evidence from literature showed that clinically relevant antibiotic resistant bacteria were present in the natural environment, that is in soil, water, air and wildlife. It was therefore hypothesised that humans in areas with high broiler densities might have an increased risk for carriage of ESBL-producing Enterobacteriaceae. This hypothesis was rejected, as the observed risk was lower for these individuals. The situation might be different for individuals living on broiler farms as ESBL-producing E. coli were detected on all investigated farms. Among broilers, the within farm prevalence approached 100%, and there was no difference between conventional and organic farms at five weeks, i.e. just before slaughter on conventional farms. On organic farms, the prevalence decreased to 80.0% at 70 days, i.e. slaughter age. Not only transmission to humans via the farm environment, but close physical contact with broilers might, therefore, lead to increased risk for carriage. Prevalence among farmers, their family members and employees on both conventional (19.1%) and organic (18.5%) broiler farms was higher compared to humans in the general population (5.1%). Moreover, people in close contact with live broilers showed the highest risk (27.1 vs. 14.3%). Evidence for clonal transmission of ESBL-producing E. coli between humans and broilers was found on conventional farms, and horizontal gene transfer was suspected on both conventional and organic farms. Even without selection pressure from antibiotics ESBL-producing E. coli were able to transmit and persist in an organic broiler flock, which shows that broilers form a reservoir of antibiotic resistance genes. This leads to an increased risk of carriage of humans on farms through direct contact with broilers and possibly via the direct farm environment. As only a very small percentage of the general population is exposed to live broilers, direct contact with broilers does not appear to be important for carriage in the general human population.

Emerging mosquito-borne viruses: transmission and modulation of host defence
Fros, J.J. - \ 2015
Wageningen University. Promotor(en): Just Vlak; Willem Takken, co-promotor(en): Gorben Pijlman. - Wageningen : Wageningen University - ISBN 9789462574243 - 190
west-nijlvirus - chikungunyavirus - ziekteoverdracht - ziekten overgebracht door muskieten - west nile virus - chikungunya virus - disease transmission - mosquito-borne diseases

Summary

Two highly pathogenic arthropod-borne (arbo)viruses, West Nile virus (WNV) and chikungunya virus (CHIKV), recently (re-)emerged in both Europe and the Americas. This resulted in large-scale epidemics of severe encephalitic and arthritogenic human disease, respectively. Both viruses replicate in their vertebrate hosts and mosquito vectors to complete their respective transmission cycles. In mosquitoes, arbovirus infections lead to relatively high viral titres without causing notable disease symptoms or fitness costs, whereas virus replication in the vertebrate host initiates strong antiviral responses and can be highly pathogenic and sometimes deadly.

WNV is a flavivirus (family Flaviviridae; genus Flavivirus), that finds its origin in Africa. The introduction of lineage 1 WNV into North America in 1999 caused the largest outbreak of human neuroinvasive disease to date. In southern Europe, a highly pathogenic lineage 2 strain has recently established itself in 2010, causing annual outbreaks. Additionally, the related flavivirus Usutu virus (USUV), has also emerged in Europe. Both WNV and USUV are transmitted by mainly Culex mosquitoes between avian amplifying hosts, but also frequently infect humans and horses. USUV and WNV co-circulate in parts of southern Europe, but the distribution of USUV extends further into central and north-western Europe.

In this thesis the potential spread of both WNV lineages through Europe is investigated by determining how effectively north-western European common house mosquitoes (Culex pipiens) transmit WNV. The results were compared to the transmission rates of USUV. North-western European mosquitoes were found to be highly competent vectors for both pathogenic lineages of WNV, which underscores the epidemic potential of WNV in Europe. Interestingly, American Culex pipiens only efficiently transmitted WNV lineage 1 but not the European lineage 2, which indicates a high degree of genotype-genotype specificity in the interaction between virus and vector. Furthermore, by comparing blood meal infection with intrathoracic injection of mosquitoes with WNV, the differential transmission rates of WNV lineage 2 could be attributed to infection barriers at the midgut level. In the vector competence studies, European mosquitoes were also found to be highly competent for USUV transmission. Interestingly, at higher temperatures USUV infected significantly more mosquitoes as compared to WNV. This indicates that mosquitoes from WNV-free areas are intrinsically capable of transmitting both pathogenic WNV lineages and explains the current localized WNV activity in southern Europe.

In addition, the infection rates of WNV and USUV were both enhanced at higher temperatures. This implies further epidemic spread of WNV and/or USUV during periods with favourable climatic conditions. Finally, as both viruses utilize the same vector and reservoir species, the higher infection rate of USUV suggests that this virus may precede WNV transmission in Europe. This presses the need for intensified surveillance of virus activity in current WNV-free regions and warrants increased awareness in the clinic throughout Europe

In contrast to WNV, CHIKV (Family Togaviridae; genus Alphavirus) is transmitted in an urban transmission cycle involving humans and two major mosquito species: Aedes aegypti and Aedes albopictus. These invasive, originally African and Asian mosquito species are the drivers of the recent CHIKV outbreaks in Europe and the Americas. The first autochthonous CHIKV transmission on the American continent was detected in late 2013 and by the end of 2014 over a million people were diagnosed with a CHIKV infection. In humans, CHIKV can cause high fever and incapacitating arthralgia. There are no vaccines or antiviral compounds available for human use against either CHIKV (or WNV) and broad-spectrum antiviral treatments have proven ineffective. To develop novel strategies that interrupt the CHIKV transmission cycle, it is key to understand how CHIKV replicates in both vertebrates host and the mosquito vector. The molecular mechanisms that determine effective viral replication in mosquitoes are largely unknown. By studying the intracellular localization of CHIKV non-structural protein 3 (nsP3) in insect cells, an interaction between nsP3 and the endogenous mosquito protein Rasputin was uncovered and elucidated. Both proteins were found to interact via two short amino acid repeats within the C-terminus of nsP3 and the NTF2-like domain of Rasputin, forming cytoplasmic nsP3-Rin granules. Silencing of endogenous Rasputin in live Ae. albopictus mosquitoes revealed that this protein is essential for CHIKV to effectively establish transmissible infections. This is the first reported function of mosquito Rasputin in arbovirus infection.

Vertebrate cells express two proteins that are homologue to mosquito Rasputin, namely Ras-GAP SH3 domain-binding protein (G3BP) 1 and 2. G3BP proteins are crucial components of mammalian stress granules (SG), which are RNA triage centers that form during environmental stress, leading to impaired translation of most mRNAs. In co-localization studies in mammalian cells it is shown how CHIKV nsP3 sequesters G3BP into viral nsP3-G3BP granules. By making G3BP unavailable, nsP3 inhibits a bona fide SG response. The evidence obtained in these studies contributes to the growing evidence that cellular SGs possess antiviral activity, yet at the same time indicate a novel, proviral role for Rasputin during infection of the mosquito vector.

In mammalian cells, cytoplasmic pattern recognition receptors (PRR) localize to SGs. These PRRs recognize specific viral molecular patterns and upregulate the expression of interferon (IFN), activating the most potent vertebrate antiviral response, the IFN-response. The IFN-response is sufficient to clear most arbovirus infections, but administering IFN in response to CHIKV infections is ineffective. Experiments in this thesis show that CHIKV replication is resistant to IFN once RNA replication has been established, because CHIKV actively prevents IFN-induced gene expression via the inhibition of the down-stream JAK-STAT signaling pathway. In response to extracellular IFNs, this pathway activates STAT proteins, which then dimerise and translocate to the nucleus to activate antiviral gene transcription. WNV and other flaviviruses have evolved specific mechanisms to evade and inhibit the IFN-response, while alphaviruses such as CHIKV cause general host shut-off to prevent antiviral gene expression. Clear evidence is now obtained that in addition to general host shut-off, CHIKV nsP2 inhibits the JAK-STAT signaling pathway in a specific manner. Genetic evidence is presented which reveals that nsP2 independently affects RNA replication, CHIKV induced host shut-off and cytopathicity, and JAK-STAT signaling. Additional data shows that the activation and nuclear translocation of STAT is unaffected by nsP2, but that the C-terminal domain of nsP2 within the nucleus is sufficient to quickly redirect STAT dimers out of the nucleus. This host shut-off-independent inhibition of IFN signaling by CHIKV nsP2 is likely to have an important role in viral pathogenesis.

In the final phase of viral replication, viral envelope proteins mature in the endoplasmic reticulum (ER) before they translocate to the plasma membrane. When the ER-protein folding load becomes too high, unfolded and misfolded proteins in the ER will activate the unfolded protein response (UPR). Transient expression of CHIKV envelope glycoproteins are now shown to have the potential to induce the UPR. The UPR aims to reduce general protein synthesis and increase the protein-folding capacity of the ER. CHIKV infection resulted in the phosphorylation of eukaryotic translation initiation factor 2, but did not increase the expression of well-known UPR target genes. In addition, functional X-box-binding protein 1 did not translocate into the nucleus during CHIKV infection. Individual expression of CHIKV nsPs revealed that nsP2 alone was sufficient to inhibit the UPR. Mutations that rendered nsP2 unable to cause host-cell shut-off prevented nsP2-mediated inhibition of the UPR. This indicates that initial UPR induction takes place in the ER but that expression of functional UPR transcription factors and target genes is efficiently inhibited by CHIKV nsP2.

Finally, this thesis describes how effectively potential mosquito vectors transmit the flaviviruses WNV and USUV and provides novel insights on the underlying molecular mechanisms that enable CHIKV to accomplish successful infections in both its human host and mosquito vector. The effective inhibition of the JAK-STAT signaling pathway, combined with host shutoff, induced by nsP2 provides a rationale for the ineffectiveness of broad-spectrum antivirals against acute arbovirus infections and suggests directing future antiviral drug development to more specific compounds that directly interfere with viral replication and transmission. The uncovered interaction between CHIKV nsP3 and Rasputin/G3BP may provide such a target as disturbing this interaction could potentially re-instate cellular stress responses and interfere with viral replication and transmission.

Foot-and-mouth disease virus : the role of infection routes and species differences in the transmission of FMDV
Bravo De Rueda Cabrera, C. - \ 2015
Wageningen University. Promotor(en): Mart de Jong, co-promotor(en): Aldo Dekker; Phaedra Eble. - Wageningen : Wageningen University - ISBN 9789462573284 - 137
mond- en klauwzeervirus - mond- en klauwzeer - infectieziekten - ziekteoverdracht - ziektebestrijding - infectiebestrijding - soortverschillen - epidemiologie - diergeneeskunde - foot-and-mouth disease virus - foot and mouth disease - infectious diseases - disease transmission - disease control - infection control - species differences - epidemiology - veterinary science

ÁFoot-and-mouth disease is a contagious viral disease of cloven-hoofed animals (e.g. cattle, sheep, pigs) and can cause severe economic losses to the farm animal industries. The aim of this thesis was to quantify underlying mechanisms regarding transmission of FMDV. With data from past animal experiments we identified the factors which are associated with the amount of virus shed by infected animals and thus may be of importance for transmission of the virus. In an experimental study, the contribution of the environment on the transmission of FMDV was investigated by using a new mathematical model in which the contribution of the environment on transmission was incorporated. Roughly 44% of the transmission of FMDV occurred through the environment that was contaminated with se-excretions from FMDV infected animals. The role of the different species on the transmission of FMDV was investigated with a transmission study of FMDV between infected sheep and naïve cattle. Sheep were found to be less infectious than cattle but similarly susceptible. Using a so-called next-generation matrix, transmission of FMDV in mixed cattle-sheep populations (with different proportions of cattle and different proportions of vaccinated animals) was quantified and the effects of different vaccination strategies against FMDV were analysed. In mixed populations of cattle and sheep, transmission of FMDV is higher when more cattle are present. In populations with more than 14% cattle, targeting vaccination to cattle only can be sufficient to control FMDV.

The results of this thesis show that transmission of FMDV can occur via a contaminated environment, (without animal presence) and that sheep seem to play a limited role in the transmission of FMDV. These results can be used to improve the control measures to prevent and control FMDV in different animal populations.

Augustaziek bij tulp : Eindrapportage ‘Inzicht in de symptoomontwikkeling van Augustaziek tijdens de bolproductie en broeierij'
Verbeek, M. ; Stijger, C.C.M.M. ; Dam, M.F.N. van; Lans, A.M. van der; Lemmers, M.E.C. ; Haaster, A.J.M. van - \ 2014
Lisse : Praktijkonderzoek Plant & Omgeving BBF - 29
tulpen - plantenvirussen - necrovirus - olpidium brassicae - schade - ziekteoverdracht - bodemschimmels - siergewassen - bloembollen - cultuurmethoden - landbouwkundig onderzoek - tulips - plant viruses - damage - disease transmission - soil fungi - ornamental crops - ornamental bulbs - cultural methods - agricultural research
Augustaziek bij tulp wordt veroorzaakt door het Olive mild mosaic virus (OMMV), een virus dat behoort tot het geslacht Necrovirus (waar ook het tabaksnecrosevirus (TNV) toe behoort). Dit virus kan plantenwortels infecteren vanuit de grond, een proces dat vele malen efficiënter wordt wanneer de virusdeeltjes via zwermsporen van de wortels-infecterende bodemschimmel Olpidium brassicae worden overgebracht. Schimmel en virus komen pleksgewijs in verschillende grondsoorten voor en leven op allerlei gewassen en onkruiden. Augusta komt in bepaalde jaren meer voor dan in andere jaren. Er wordt soms over een cyclus van ongeveer 12 jaar gesproken waarin zogenaamde Augusta-jaren voorkomen. Het onderzoek waarin in dit verslag wordt gerapporteerd had als uitgangspunt drie vragen: • Wanneer Augustaziek uitdooft in een partij, is het virus dan echt afwezig, of heeft men met een latente (niet zichtbare) infectie te maken? Genezen van virus is nl. geen gangbaar verschijnsel in de plantenwereld. • Hoe groot is het risico op zichtbare schade in de broei van een partij die op het veld zichtbare Augusta-schade vertoonde? Kan de schade in de broei voorspeld worden? • Zijn er factoren/indicatoren die een ‘Augusta-jaar’ aankondigen? Om een idee te krijgen over de mogelijke antwoorden op deze vragen is als eerste een enquête gehouden onder tulpentelers (bollenteelt en afbroei). Aan de hand van die enquête is gekeken naar o.a. teeltomstandigheden, perceel, voorvrucht etc. Ook is aan deze telers gevraagd of zij materiaal beschikbaar wilden stellen van partijen waarin zij eerder Augusta-schade hadden waargenomen. Deze partijen zijn opgeplant in de kas onder afbroei-omstandigheden en op het veld onder bollenteelt-omstandigheden. Tijdens deze teelten werd de symptoomontwikkeling gevolgd en werden virustoetsen uitgevoerd om de infectie met OMMV te monitoren. Bij enkele planten met symptomen is met behulp van Next Generation Sequencing gekeken of ook daadwerkelijk OMMV betrokken was bij het ziektebeeld. Hieruit bleek dat er in enkele planten andere virussen dan OMMV voorkwamen die symptomen veroorzaakten die waarschijnlijk in de praktijk moeilijk van Augusta kunnen worden onderscheiden. Voorbeelden van deze virussen zijn het tulpenvirus X, Arabis mozaïekvirus, dravikmozaïekvirus, tabaksratelvirus en het vroege-verbruiningsvirus van erwt. Hoewel op bovenstaande vragen nog geen duidelijke antwoorden te geven zijn, is wel een stapje in de goede richting gezet. Uit dit onderzoek zijn de volgende inzichten verkregen: • Symptomen in tulp die in de praktijk Augustaziek worden genoemd worden over het algemeen veroorzaakt door infectie met OMMV, maar ook andere virussen kunnen op Augusta lijkende schadebeelden geven. • OMMV lijkt in de afbroei ook symptoomloos te kunnen voorkomen, maar dat zal afhankelijk zijn van cultivar en teeltomstandigheden (over het algemeen wordt aangenomen dat bij hogere temperaturen minder schade wordt waargenomen). • Een aantal partijen die als Augustapartijen waren aangemerkt bleken vrij te zijn van OMMV in de virustoets in het leverbaar materiaal en in de boltoetsen na kasteelt en veldteelt. Tijdens deze teelten werd geen schade waargenomen in deze partijen. Of dit ook daadwerkelijk betekent dat uitdoving heeft plaatsgevonden is niet te concluderen omdat ten tijde van de waarneming van de symptomen de zieke planten niet op virusinfecties zijn getoetst.
Inventarisatie zoönosen bij het paard in Nederland
Swanenburg, M. ; Vos, C.J. de; Visser, E.K. ; Nodelijk, G. - \ 2014
Lelystad : CVI Wageningen UR (CVI report 14/CVI0155) - 62
dierenwelzijn - paarden - ziekten - diergezondheid - zoönosen - volksgezondheid - risicoschatting - inventarisaties - ziekteoverdracht - animal welfare - horses - diseases - animal health - zoonoses - public health - risk assessment - inventories - disease transmission
Het ministerie van EZ heeft laten onderzoeken of het paard in Nederland een rol speelt bij het ontstaan van infectieziekten die kunnen worden overgedragen van dieren op mensen (zoönosen).
Bestrijding van Phytophthora-vruchtrot bij peer (Conference)
Wenneker, M. ; Werd, H.A.E. de; Pham, K.T.K. - \ 2014
Randwijk : Praktijkonderzoek Plant & Omgeving, Business Unit Bloembollen, Boomkwekerij en Fruit - 22
peren - pyrus communis - phytophthora - vruchtrot - plantenziekten - aantasting - detectie - methodologie - bodemschimmels - real time pcr - bestrijdingsmethoden - ziekteoverdracht - pears - fruit rots - plant diseases - infestation - detection - methodology - soil fungi - control methods - disease transmission
De afgelopen jaren werd op verschillende perenpercelen (zware) aantasting met Phytophthora-vruchtrot vastgesteld. Ook in de bewaring werd aantasting van Phytophthora geconstateerd. Naar aanleiding daarvan is een project gestart met de volgende doelstellingen: • Het leveren van basiskennis over de epidemiologie en infectiewijze van Phytophthora bij peer. • Aanzet voor ontwikkelen van mogelijke bestrijdingsstrategiën voor Phytophthora-vruchtrot.
Aanpak van Burkholderia gladioli in gladiool
Dam, M.F.N. van; Dijkema, M.H.G.E. - \ 2014
Lisse : Praktijkonderzoek Plant & Omgeving, Sector Bomen, Bollen & Fruit - 29
bloembollen - gladiolus - burkholderia - bacterieziekten - bestrijdingsmethoden - ziekteoverdracht - besmetting - tests - verdedigingsmechanismen - ziekteresistentie - ornamental bulbs - bacterial diseases - control methods - disease transmission - contamination - defence mechanisms - disease resistance
Wateroverlast in een Teelt de grond uit-systeem kan grote schade geven aan lelies. Drie dagen wateroverlast in augustus leidde in dit onderzoek tot grote opbrengstderving. Eén dag wateroverlast in september of in oktober veroorzaakte nauwelijks uitval of een lager bolgewicht bij de oogst. Wateroverlast leidt tot ethanolvorming in de bollen. De ethanolvorming vertoonde dit jaar geen mooi verband met de tijd: drie dagen wateroverlast gaf meer ethanol dan één of twee dagen, maar twee dagen niet meer dan één. In 2013 vertoonde de concentratie ethanol een rechtlijnig verband met de duur van de wateroverlast. De voorspellende waarde van een ethanolmeting blijkt na de experimenten in 2014 minder zeker. Het beluchten van het natte substraat door het doorblazen van perslucht leidde bij de behandeling in augustus tot minder ethanolvorming, maar juist tot meer opbrengstderving. Het systeem van beluchting via een slang onderin het substraat had een iets gunstiger effect op de ethanolvorming dan beluchting via slangetjes, die in het substraat gestoken waren. De grotere opbrengstderving door beluchting tijdens de periode van wateroverlast is mogelijk een gevolg van mechanische beschadiging van de (haar)wortels door de beweging, of van structuurbederf die optreedt als het doorborrelde substraat weer droogvalt. Dit onderzoek bevestigt de conclusie uit 2013 dat lelies bestand zijn tegen maximaal 1 dag wateroverlast (anaerobie). Een periode van anaerobie leidt tot ethanolvorming in de bollen, maar de correlatie tussen duur van de anaerobie is te zwak om het ethanolgehalte als indicator toe te passen. Het beluchten van grond tijdens periodes van wateroverlast is geen oplossing voor het anaerobieprobleem.
Vogelgriepvirus kwam aanvliegen uit Azië
Sikkema, A. ; Bouwstra, R.J. - \ 2014
Resource: weekblad voor Wageningen UR 9 (2014)8. - ISSN 1874-3625 - p. 8 - 8.
aviaire influenza - aviaire influenzavirussen - besmetting - pluimveehouderij - pluimvee - diergezondheid - dierenwelzijn - ziekteoverdracht - dierlijke productie - avian influenza - avian influenza viruses - contamination - poultry farming - poultry - animal health - animal welfare - disease transmission - animal production
CVI acht besmetting via trekvogels 'waarschijnlijk.' Het virus komt oorspronkelijk uit China.
Intervention methods to control the transmission of noroviruses and other enteric and respiratory viruses
Tuladhar, E. - \ 2014
Wageningen University. Promotor(en): Marcel Zwietering, co-promotor(en): E. Duizer; Rijkelt Beumer. - Wageningen : Wageningen University - ISBN 9789462571129 - 163
norovirus - gastro-enteritis - uitbraken (ziekten) - ziekteoverdracht - voedselbesmetting - ademhalingsziekten - voedselmicrobiologie - gastroenteritis - outbreaks - disease transmission - food contamination - respiratory diseases - food microbiology

Intervention methods to control the transmission of noroviruses and other enteric and respiratory viruses

Era Tuladhar

Abstract

Human noroviruses are the leading cause of acute and outbreak associated gastroenteritis worldwide. The outbreaks occur often in hospitals, nursing homes, health care centers as well as in individual homes. Due to the high number of outbreaks and frequency of infection, the burden of disease is high. The virus transmission takes place from person to person directly through the fecal oral route or indirectly through contaminated surfaces or consumption of contaminated food. This study aimed to investigate methods to reduce the burden of disease caused by norovirus and focuses on reducing the transmission through hands and contaminated surfaces. Besides human norovirus, other enteric and respiratory viruses are also transmitted through these routes and were included in the study. Enteric viruses included in the study were human norovirus GI.4 and GII.4, poliovirus Sabin1, rotavirus SA11, parechovirus 1 and murine norovirus 1 (MNV1). The respiratory viruses were adenovirus type 5 and influenza A (H1N1) virus. These viruses can contaminate food through food handler-related contamination. Heating and pasteurizing is a commonly used method for inactivation of microorganisms in food. Heating at commonly used temperatures of 56°C and 73°C showed that thermo-stability of parechovirus and influenza virus was found to be similar to that of proven foodborne viruses and heating at 73°C for 3 min is sufficient to reduce the infectivity of the tested viruses > 4 log10. Not only food, contaminated hands can also transfer viruses to different surfaces, which are then sources of further transmission of the viruses. Cleaning and disinfection of contaminated surfaces are common intervention methods used in health care and kitchen facilities. The enteric and respiratory viruses showed varying susceptibility to cleaning and disinfection procedures applied. Data on infectious doses and transfer efficiencies was used to estimate a target level to which the residual contamination should be reduced and it was found that a single wipe with liquid soap followed by a wipe with 250 ppm free chlorine solution was sufficient to reduce the residual contamination to below the target level for most of the pathogens tested. Spot disinfection by 1000 ppm chlorine solution after wiping with liquid soap was sufficient to reduce the genomic copies of human norovirus GI.4 and GII.4 (> 5 log10 PCRU) completely within 10 min. In addition to manual cleaning and disinfection, non-touch disinfection of contaminated surfaces by vaporized hydrogen peroxide disinfection at 127 ppm for 1 h, as approved disinfection in the Netherlands for hospitals and health care centers, is effective against poliovirus Sabin 1, rotavirus SA11, adenovirus type 5 and MNV1 on stainless steel, framing panel (> 4 log10 infectivity reduction) and gauze (> 2 log10 infectivity reduction). Beside non-touch disinfection, immobilized biocidals have been tested for disinfection of contaminated surfaces. Immobilized quaternary ammonium compound coatings were virucidal against the influenza virus within 2 min but no virucidal effect against poliovirus was found in 6 h. Thus the coating can be used against the influenza A virus to prevent the transmission through frequently touched sites but not for non-enveloped viruses. Our study demonstrated that a norovirus contaminated hand can transfer the viruses to different surfaces, including food, even after the virus is dried. As an intervention method to prevent the transmission of the virus, washing hands with soap and water (> 5 log10 PCRU reduction) is better than using alcohol based hand disinfectants in removing noroviruses from hands.

This research has delivered new insights in methods to reduce transmission of human norovirus and produced comparative quantitative data on intervention methods to control transmission of other enteric and respiratory viruses. The study has additionally contributed to a better understanding of human norovirus transmission intervention efficiency. The new insights allow for the development of science based guidelines to control norovirus and other enteric and respiratory viruses in outbreak settings and thus help to reduce the burden of illness caused by these viruses.

On the role of the polychaete Dendronereis spp. i the transmission of white spot syndrome virus in shrimp ponds
Desrina, Haryadi - \ 2014
Wageningen University. Promotor(en): Johan Verreth; Just Vlak, co-promotor(en): Marc Verdegem. - Wageningen : Wageningen University - ISBN 9789462570856 - 181
polychaeta - witte-vlekken-syndroom-virus - garnalen - ziekteoverdracht - visvijvers - garnalenteelt - voer - reservoir hosts - aquacultuur - white spot syndrome virus - shrimps - disease transmission - fish ponds - shrimp culture - feeds - aquaculture

White spot syndrome virus (WSSV) is by far the most devastating shrimp virus. Control measures have lowered the WSSV incidence to various degrees, but the pathogen remains plaguing shrimp culture worldwide. Continuous exposure may cause WSSV to adapt and infect non-crustacean benthic fauna in ponds such as polychaetes, hence, extending WSSV host range to maintain virus persistence in ponds. Dendronereis spp. (Pieters 1854) are ubiquitous Nereid polychaetes in shrimp ponds in Indonesia and part of the shrimp’s natural diet. This thesis aimed to investigate the possible role of Dendronereis spp. in the transmission of WSSV in shrimp ponds. The significance of the findings may provide new insight on the persistence of WSSV in the pond environment and novel strategies for disease management. The investigation started with a survey to determine the occurrence of WSSV in Dendronereis spp. in Indonesia, followed by subsequent laboratory observations to determine the role of Dendronereis spp. in white spot syndrome disease development. Field surveys in selected ponds in two research locations in Indonesia, the Mahakam delta (East Kalimantan) and the vicinity of Semarang (Central Java), showed that WSSV infection in Dendronereis spp. is quite common. Point prevalence of WSSV infected Dendronereis spp. was 44 ± 27% (± SD). The average prevalence in Mahakam delta was 73 ± 22% and in Java 26 ± 38%. This result implied that WSSV-infected Dendronereis spp. are widely distributed. WSSV replicated in the gut of naturally-infected Dendronereis spp. as detected in cell nuclei via immunohistochemistry (IHC) using monoclonal antibodies and via RT-PCR to detect the viral mRNA. These experiments showed that Dendronereis spp. are natural and susceptible hosts of WSSV. WSSV was transmitted from naturally infected Dendronereis spp. to Litopenaeus vannamei (Boone 1931) through the oral route and further to new naïve shrimp showing natural transmission of WSSV from polychaetes to shrimp. This indicates that the transmission of WSSV from polycheates to shrimp is possible. An experiment using Hediste diversicolor (O.F. Müller 1776) as a more amenable alternative model animal to study WSSV infection in polychaetes showed that this polychaete was not susceptible to WSSV infection using methods commonly used to induce infection in shrimp. In ponds, WSSV infection incidence in Dendronereis spp. correlated positively with Dendronereis spp. density and with the proportion of WSSV infection in shrimp. Findings of the present study underscore that Dendronereis spp., as ubiquitous and resident animals in the shrimp ponds can be reservoir hosts of WSSV and responsible for disease transmission. However, further studies are needed to obtain a better understanding of the importance of Dendronereis spp in WSSV epidemiology in and beyond shrimp ponds.

Effect of species richness on disease risk: dilution effect and underlying mechanisms
Huang, Z. - \ 2014
Wageningen University. Promotor(en): Herbert Prins, co-promotor(en): Fred de Boer; Frank van Langevelde. - Wageningen : Wageningen University - ISBN 9789462570894 - 73
dierziekten - bovidae - rundvee - risico - soortenrijkdom - ziektedistributie - pathogenen - ziekteoverdracht - modellen - afrika - animal diseases - cattle - risk - species richness - disease distribution - pathogens - disease transmission - models - africa

Summary

any pathogens infect multiple host species which can differ in their reservoir competence. Consequently the species richness and composition of the host community can considerably influence the dynamics of disease transmission.

Recently, an increasing number of studies reported the existence of a dilution effect whereby high host species richness reduces the disease risk. However, the generality of the dilution effect and its mechanisms are still highly debated.

In this thesis, I tested the existence of a dilution effect in bovine tuberculosis (BTB) and investigated the underlying mechanisms of the dilution effect.

I detected a possible dilution effect in BTB, where higher mammal species richness reduced the probability of occurrence of BTB at a regional level in Africa, after correcting for cattle density (Chapter 2).

This dilution effect might be caused by encounter reduction, i.e. the presence of non-competent mammal species might act as barriers to herd movement of cattle and reduce encounter rates among herds, which leads to a decreased probability of BTB outbreaks.

Then I extended the study of the BTB dilution effect to the analysis of BTB persistence and recurrence (Chapter 3).

The results showed that mammal species richness was also negatively correlated with the BTB persistence and recurrence.

Besides, I demonstrated that the presence of African buffalo, as a maintenance host for

Mycobacterium bovis (the causative agent of BTB), had a positive identity effect and increased the risk of BTB persistence and recurrence, whereas greater kudu distribution was not correlated with BTB persistence or recurrence.

In addition, BTB persistence and recurrence were correlated with different sets of risk factors.

In Chapter 4, I showed that interspecific variation in species’ reservoir competence could be partly explained by life-history traits in three vector borne diseases, namely Lyme disease, West Nile Encephalitis (WNE) and Eastern Equine Encephalitis (EEE). Species with larger body mass (for hosts of Lyme disease and WNE) or smaller clutch size (for hosts of EEE) had a lower reservoir competence. Given that both larger body mass and smaller clutch size are linked to higher extinction risk of local populations, the results indicate that species with a higher reservoir competence are more likely to remain in the community when biodiversity declines, and thereby potentially increase the risk of transmitting these pathogens.

This might be a possible mechanism underlying the dilution effect.

Combing the results about the relationships between species’ reservoir competence and life-history traits, I constructed a compartmental model to investigate the effect of connectivity on the risk of directly transmitted diseases in metapopulations (Chapter 5).

I showed that different indicators of disease risk (infection prevalence and number of infected individuals) reacted differently to increasing connectivity.

Higher connectivity can not only decrease disease risk due to the dilution effect by increasing species richness, but can also increase disease risk through increasing contact rates among patches (facilitation effect).

The net impact of connectivity depends on the relative importance of the dilution versus facilitation effect.

These results may reconcile the current debate on the dilution effect, and contributes to a better understanding of the impacts of fragmentation on disease risks and the generality of the dilution effect.

M Finally, I combined these findings and reviewed the evidence and critiques on the dilution effect (Chapter 6).

Latest studies (also the BTB study in this thesis) tried to test species identity effects, caused by particular species in communities, and found that the identity effect and dilution effect can operate simultaneously in the host community.

I suggest that the identity effect could act as an additional mechanism explaining the effect of species richness on disease risk.

A weak correlation between host reservoir competence and local extinction risk can create inconsistent effects of host species richness on disease risk.

Moreover, different indicators of disease risk may react differently to the changes in species richness.

This could also be one of the reasons for the controversial results from previous studies that used different indicators (e.g., prevalence or number of infection) of disease risk.

In conclusion, this thesis presents both evidence and critique for the existence of the dilution effect.

Since factors may simultaneously influence community compostion and the characteristics of pathogen transmission (e.g., susceptibility, survival of pathogen etc.), future studies should also consider these factors, rather than only species richness, to better understand the effect of species richness on disease risk.

Mechanisms underlying disease transmission between spatially separated animals
Bunnik, B.A.D. van - \ 2014
Wageningen University. Promotor(en): Mart de Jong, co-promotor(en): Thomas Hagenaars; Gonnie Nodelijk. - Wageningen : Wageningen University - ISBN 9789461739537 - 150
dieren - vleeskuikens - infectieziekten - ziekteoverdracht - gastheren (dieren, mensen, planten) - wiskundige modellen - epidemiologie - diergeneeskunde - animals - broilers - infectious diseases - disease transmission - hosts - mathematical models - epidemiology - veterinary science

Transmission of infections between spatially separated hosts is a common problem, not only during major outbreaks of livestock diseases, but also in many other settings such as the transmission of infectious diseases between plants and crops or in healthcare settings. During the last major epidemics of livestock diseases in the Netherlands and abroad, disease transmission events occurred despite movement bans and other (bio-)security measures, implying that indirect transmission plays a major role. A better understanding of indirect transmission is necessary to put in place evidence based bio-security measures against neighbourhood (indirect) transmission. To gain more insight in the mechanisms underlying indirect transmission a series of experimental studies combined with mathematical modelling were conducted of which the results are presented in this thesis. First the effect of acidification of drinking water on the transmission parameters of direct and indirect transmission of Campylobacter jejuni (C. jejuni) between broilers was studied. It was shown that acidified drinking water has an effect on indirect transmission but not on direct transmission of C. jejuni between broilers. The sender and receiver sub-process of indirect transmission was then studied in more detail and it was shown that a significant negative interaction effect between acidification of the sender and receiver sub-processes exists, indicating that there is no additional effect of acidification of the drinking water on both sides of the transmission process compared to acidified drinking water only on one side. To study the transport of the pathogen in the environment in more detail, a series of indirect transmission experiments was carried out and a model framework was developed to study indirect transmission between spatially separated hosts. These studies showed that indirect transmission of C. jejuni between broilers is best described by a multistage environmental route from sending to receiving animal, suggesting that indirect transmission occurs through progressive (but slow) contamination of the environment surrounding the source. Indirect transmission experiments where repeated with both C. jejuni and Escherichia coli and the results showed that for C. jejuni it takes much longer for the first effective (viable) bacterium to cross the small distance of approximately 75 cm than it does for Escherichia coli. A new modelling approach to study indirect transmission was developed guided by these indirect transmission experiments. This model is capable of accurately describing the pathogen dispersal process by a diffusive transport mechanism which includes pathogen mortality. Lastly, a range of dose-response models were compared and tested how well these fitted to the data from a dose-response experiment. Here it was shown that for interpolation purposes two relatively simple models are best capable of describing the data from the dose-response experiment. For extrapolation purposes, however, it was shown that from the models that were studied a model that abides by the independent action hypothesis is best.

Effect of reducing the area under transport ban on transmission risk and piglet surplus during a CSF epidemic in the Netherlands
Hagenaars, T.H.J. ; Bergevoet, R.H.M. ; Bontje, D.M. ; Nodelijk, G. ; Backer, J.A. ; Asseldonk, M.A.P.M. van; Roermund, H.J.W. van - \ 2014
Lelystad/Wageningen : CVI/LEI (Report number CVI: 14/CVI0076 )
biggen - varkenspest - veevervoer - ziekteoverdracht - risicofactoren - dierenwelzijn - diergezondheid - varkenshouderij - veehouderij - piglets - swine fever - transport of animals - disease transmission - risk factors - animal welfare - animal health - pig farming - livestock farming
In this report, we investigate the expected effects of reducing the area in which live piglet transports are banned on transmission risk and on the piglet surplus (in the area of the transport ban) during a CSF epidemic in the Netherlands.
Risk of poultry compartments for transmission of High Pathogenic Avian Influenza
Boender, G.J. ; Hagenaars, T.H.J. ; Backer, J.A. ; Nodelijk, G. ; Asseldonk, M.A.P.M. van; Bergevoet, R.H.M. ; Roermund, H.J.W. van - \ 2014
Lelystad : CVI en LEI (Report number CVI: 14/I00028 ) - 28
aviaire influenza - pluimveeziekten - pluimveehouderij - compartimenten - ziekteoverdracht - pathogeniteit - eu regelingen - wetgeving - diergezondheid - dierenwelzijn - pluimvee - avian influenza - poultry diseases - poultry farming - compartments - disease transmission - pathogenicity - eu regulations - legislation - animal health - animal welfare - poultry
The application for a poultry compartment by VPI and the prospect of further ones motivates the Dutch Ministry of Economic Affairs and the Netherlands Food and Consumer Product Safety Authority to raise the following three questions: 1) What are the additional transmission risks that the (specific) VPI compartment poses during an HPAI epidemic, compared to a situation without compartment?; 2) What are the additional transmission risks that a compartment in general poses during an HPAI epidemic, depending on its characteristics?; 3) What are relevant evaluation criteria for granting the compartment status? In this study we addressed these questions by quantitatively assessing the veterinary risks based on mathematical model calculations, and by qualitatively discussing the (socio) economic aspects.
C-strain vaccination against Classical Swine Fever: effects on epidemic and final screening
Backer, J.A. ; Loeffen, W.L.A. ; Roermund, H.J.W. van - \ 2013
Lelystad : Central Veterinary Institute
varkenshouderij - klassieke varkenspest - vaccinatie - verspreide infecties - ziekteoverdracht - pig farming - classical swine fever - vaccination - disseminated infections - disease transmission
In this project it is evaluated how the use of C-strain vaccine instead of E2-subunit vaccine will affect the effectiveness of controlling Classical Swine Fever (CSF). To this end a CSF transmission model was developed that describes virus transmission on three different levels: between animals, between pens and between herds. The results of transmission and vaccination experiments as well as the data from the 1997/1998 CSF epidemic in The Netherlands serve to parameterize the model. With the model hypothetical epidemics are simulated under different scenarios.
Phytophthora ramorum rukt op - besmettelijke bomendoder duikt op in Nederland
Goud, J.C. - \ 2013
Boom in business 4 (2013)4. - ISSN 2211-9884 - p. 40 - 43.
houtachtige planten - struiken - rhododendron - phytophthora ramorum - aantasting - plantenziekten - symptomen - ziekteoverdracht - woody plants - shrubs - infestation - plant diseases - symptoms - disease transmission
Afgelopen jaren is op een aantal plaatsen in Nederland de beruchte plantenziekte Phytophthora ramorum opgedoken. Deze schimmelachtige ziekteverwekker heeft in Californië massale sterfte veroorzaakt onder eiken en enkele andere soorten loofbomen. Hij wordt daar Sudden Oak Death genoemd.
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