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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    Systems analysis of Mycoplasma hyopneumoniae to improve vaccine production
    Kamminga, Tjerko - \ 2017
    Wageningen University. Promotor(en): V.A.P. Martins dos Santos, co-promotor(en): P.J. Schaap; J.J.E. Bijlsma. - Wageningen : Wageningen University - ISBN 9789463436519 - 152
    interdisciplinary research - molecular biology - mycoplasma hyopneumoniae - vaccines - systems biology - systems analysis - pigs - pneumonia - animals - interdisciplinair onderzoek - moleculaire biologie - mycoplasma hyopneumoniae - vaccins - systeembiologie - systeemanalyse - varkens - longontsteking - dieren

    Mycoplasma hyopneumoniae (M. hyopneumoniae) is a bacterial pathogen that has evolved from a gram-positive ancestor and specifically colonizes the lower respiratory tract of pigs where it causes enzootic pneumonia and plays a major role in the development of respiratory disease in pigs. Whole-cell inactivated vaccines are available that lower the severity of disease and are widely applied in pig industry to prevent clinical signs and improve pig herd health. However, production of these vaccines is challenging because it is not known which bacterial components are needed for protection and complex cultivation media are needed because growth requirements are not completely understood. The aim of this thesis was to understand growth and survival strategies of M. hyopneumoniae during infection, to integrate this knowledge with metabolic modeling under conditions used for vaccine production and apply this knowledge to improve the current production process for M. hyopneumoniae vaccines.

    Chapter 1 provides a general introduction into the disease, treatment and prevention methods with a focus on vaccines. I then introduce the characteristics of the M. hyopneumoniae genome, transcriptome and review the current knowledge on infectious mechanisms and the response of the pig to infection and vaccination. Finally, I discuss the challenges related to vaccine production and introduce systems biology tools that will be applied in the thesis. In chapter 2 we define a strategy for risk-based process development of bacterial vaccines which provided the framework for future studies performed during this thesis. We propose to integrate the academic workflow for rational strain design with the industry standard for process design. Systems biology tools, especially genome-scale metabolic models, play an essential role in this strategy because application of these tools reduces process risks and increases process understanding. Therefore, in line with this strategy, we created a manually curated genome-scale metabolic model of M. hyopneumoniae which we applied to dynamically model the cultivation step in the vaccine production process (chapter 3). We found that only 16% of cellular energy in a standard fermentation was used for growth and 84% was used for non-growth associated maintenance. By model-driven experimentation we were able to increase the fraction of cellular energy used for growth by addition of pyruvate to the production medium, and showed in dedicated fermentor experiments that the improved process reached a 2.3 times higher biomass yield. Although the metabolic model helped to increase process yield, it did not allow prediction of a defined cultivation medium without components from porcine origin. Therefore, to better understand the dependency of M. hyopneumoniae on host derived components, we performed a functional comparison of 80 mycoplasma genomes and used multivariate and machine-learning algorithms to relate functional capability to the specific host and niche of mycoplasma species (chapter 4). This analysis allowed us to identify protein domains possibly needed for growth and survival in the pig lung. In addition, we found that protein domains expected to be essential for bacterial growth were not persistently present in mycoplasma genomes suggesting that alternative domain configurations exist that bypass their essentiality. To better understand whether the proteins we identified as possibly important for survival in pigs actually play a role during M. hyopneumoniae infection, we sequenced the bacterial mRNA during infection in chapter 5 and compared the in vivo transcriptome to that of broth grown mycoplasma. We found 22 up-regulated and 30 down-regulated genes during infection (FDR<0.01 and fold change >2LOG2) and identified differentially expressed ncRNAs. In chapter 6 we build upon our mycoplasma basis to further analyse the role of ncRNAs in bacterial genomes. We identified an exponential relationship between the AT content of genomes and the number of ncRNAs and propose that this relation is the result of spurious transcription, which is more likely to occur in AT rich genomes. This hypothesis is further substantiated by showing that spurious transcription demands minimal cellular energy and that overexpression of cis-binding ncRNAs in M. pneumoniae did not influence the level of proteins translated from their overlapping mRNAs. Finally, in chapter 7 I discuss four system strategies, identified in this thesis and derived from recent literature, and discuss how these strategies could be integrated in the metabolic model of M. hyopneumoniae. Lastly, I provide an outlook on the next steps needed for improvement of the production process for M. hyopneumoniae vaccines.

    In conclusion, this work provided novel insight in the metabolic capability of M. hyopneumoniae based on the proteome domain content, captured in a genome-scale metabolic model and studied under in vitro and in vivo conditions. Biomass yield of the cultivation step for vaccine production was increased and the basis was laid to further improve the production process for M. hyopneumoniae vaccines using model-based experimentation.

    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): M.C.M. Jong, co-promotor(en): B. 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.

    Dierenlab beschermt mensen
    Sikkema, A. ; Bianchi, A.T.J. - \ 2015
    WageningenWorld (2015)1. - ISSN 2210-7908 - p. 24 - 27.
    dierziekten - infectieziekten - zoönosen - virusziekten - onderzoek - diergezondheid - vaccins - aviaire influenza - q-koorts - animal diseases - infectious diseases - zoonoses - viral diseases - research - animal health - vaccines - avian influenza - q fever
    Nederland krijgt steeds meer te maken met besmettelijke dierziektes die ook mensen ziek kunnen maken, zoals vogelgriep. Om daar goed onderzoek naar te doen is een lab gebouwd waarin levende, besmette landbouwhuisdieren gehouden worden. Geen virus kan eruit ontsnappen. ‘Zelfs het DNA wordt vernietigd.’
    Economic aspects of C-strain vaccination to control Classical Swine Fever epidemics
    Bergevoet, R.H.M. ; Asseldonk, M.A.P.M. van - \ 2013
    The Hague : LEI, part of Wageningen UR (LEI memorandum : Agriculture & entrepreneurship ) - 22
    klassieke varkenspest - vaccinatie - vaccins - varkenshouderij - classical swine fever - vaccination - vaccines - pig farming
    This research is focused on economic differences of emergency vaccination in case of an outbreak of Classical Swine Fever (CSF) in a densely populated livestock area in the Netherlands. It compares the ef-fect of a vaccination to live strategy in which a C-strain vaccine is used with the effects of a E2 subunit vaccine.
    Chikungunya virus-like particle vaccine
    Metz, S.W.H. - \ 2013
    Wageningen University. Promotor(en): Just Vlak, co-promotor(en): Gorben Pijlman. - S.L. : s.n. - ISBN 9789461735652 - 139
    chikungunyavirus - virusachtige deeltjes - virusziekten - aedes albopictus - vectoren, ziekten - vaccins - vaccinontwikkeling - genexpressie - baculovirus - insecten - celcultuur vaccins - chikungunya virus - virus-like particles - viral diseases - aedes albopictus - disease vectors - vaccines - vaccine development - gene expression - baculovirus - insects - cell culture vaccines

    Chikungunya virus (CHIKV) is an arthropod-borne alphavirus (family Togaviridae) and is the causative agent of chikungunya fever. This disease is characterised by the sudden onset of high fever and long-lasting arthritic disease. First identified in Tanzania in 1952, CHIKV has re-emerged in the last decade causing large outbreaks throughout Africa, Asia and Southern Europe. Increased CHIKV spread is mainly caused by its adaptation to a new mosquito vector, the Asian tiger mosquito Ae. albopictus, which is able to colonize more temperate regions. Currently, there are no antiviral treatments or commercial vaccines available, to prevent CHIKV infections. However, increased vector spread and clinical manifestations in humans, have triggered vaccine development. A broad range of vaccine strategies have been proposed and described, including inactivated virus formulations, live-attenuated virus, chimeric virus vaccines, DNA vaccines, adenoviral vectored vaccines, subunit protein vaccines and virus-like particle (VLP) formulations. However, these vaccination strategies have specific limitations in manufacturing, immunogenicity, safety, recombination and large scale production. Many, if not all safety problems do not apply for subunit or VLP based vaccines, except for the recombinant origin of the vaccine.

    Recently, a CHIKV VLP-based vaccine was developed and provided protection in both mice and non-human primates. Even though this VLP approach is a safe, efficient and promising alternative to other vaccine strategies, large scale DNA plasmid transfection into mammalian cells and VLP yield of transfected cells remains challenging in terms of industrial production. These problems are alleviated by using the recombinant baculovirus-insect cell expression system.

    In this thesis, recombinant baculoviruses were constructed to produce CHIKV glycoprotein E1 and E2 subunits and VLPs.For the production of CHIKV-E1 and E2 subunits, both protein genes were cloned downstream the polyhedrin gene (polh) promoter of in an Autographica californica multiple nucleopolyhedrovirus backbone, together with their authentic signal peptides 6K(E1) and E3(E2). Deletion of the C-terminal transmembrane domain, generated secreted versions of E1 (E1ΔTM or sE1) and E2 (E2ΔTM or sE2). A substantial amount of recombinant protein was glycosylated and processed by furin. The secreted CHIKV subunits were purified from the medium and were able to induce neutralizing antibodies in rabbits. For the production of the VLPs, the complete structural polyprotein (capsid, E3, E2, 6K, E1) was cloned downstream the AcMNPV polh promoter. E3E2 precursor processing and glycosylation appeared to be more efficient when E3E2 were expressed as part of the whole structural polyprotein cassette, compared to the individually expressed E3E2. The VLPs were isolated from the medium fraction and were morphologically similar to wild type CHIKV. A similar strategy was used to produce VLPs from another alphavirus, the salmonid alphavirus (SAV). Here, however, the normal baculovirus expression temperature of 27°C appeared to be detrimental for SAV-E3E2 furin cleavage and SAV-VLP production. E2-glycoprotein processing was shown to be temperature dependent and a tailored temperature-shift regime was designed in which Sf9-cells were infected with a recombinant baculovirus expressing the SAV structural proteins, and incubated at 27°C for 24 h, followed by a processing phase of 72 h at 15°C. Using this temperature regime, SAV-VLPs were produced that were morphologically indistinguishable from wild type SAV and underscores the flexibility of the baculovirus-insect cell expression system.

    The immunogenicity of purified CHIKV-sE1 and -sE2 subunits and purified CHIKV-VLPs were then tested in a lethal vaccination-challenge mouse model, in IFN α/β, -γ receptor null AG129 mice. The innate immune system of these mice was made dysfunctional. This vaccine-challenge study clearly showed that VLPs provided superior protection, compared to their subunit counterparts. The subunits provided only partial protection and induced low neutralizing antibody titres. Immunization with the VLPs fully protected mice against lethal challenge and induced significant higher neutralizing antibody titress. Even though neutralizing antibody titres were lower after subunit immunization, this study showed that a minor neutralizing antibody response is sufficient to protect mice from lethal CHIKV challenge. Next, the CHIKV VLPs were tested for their ability to induce complete protection in an adult wild-type immune-competent mouse model, in which mice develop arthritic disease after CHIKV infection. The VLPs were able to induce full protection after a single immunization of 1 µg VLPs, without the use of adjuvants. In addition, IgG isotyping revealed a balanced IgG1-IgG2c response, suggesting a role for both humoral and cellular immunity in the protection against CHIKV infection. Mice served as a proxy for primates and vaccination trials in primates are next on the agenda.

    This thesis is a typical example of the opportunities for the recombinant baculovirus-insect cell expression system in viral vaccine development, especially in vaccine development for other arboviruses. Although the CHIKV-VLPs produced in insect cells are amenable for large-scale production, the production process and downstream processing need to be carefully designed and optimized before CHIKV VLPs can be produced on an industrial scale. However, the data presented in this thesis show that CHIKV-VLPs produced in insect cells using recombinant baculoviruses represents as a new, safe, non-replicating and effective vaccine candidate against CHIKV infections.

    Chikungunya virus (CHIKV) is an arthropod-borne alphavirus (family Togaviridae) and is the causative agent of chikungunya fever. This disease is characterised by the sudden onset of high fever and long-lasting arthritic disease. First identified in Tanzania in 1952, CHIKV has re-emerged in the last decade causing large outbreaks throughout Africa, Asia and Southern Europe. Increased CHIKV spread is mainly caused by its adaptation to a new mosquito vector, the Asian tiger mosquito Ae. albopictus, which is able to colonize more temperate regions. Currently, there are no antiviral treatments or commercial vaccines available, to prevent CHIKV infections. However, increased vector spread and clinical manifestations in humans, have triggered vaccine development. A broad range of vaccine strategies have been proposed and described, including inactivated virus formulations, live-attenuated virus, chimeric virus vaccines, DNA vaccines, adenoviral vectored vaccines, subunit protein vaccines and virus-like particle (VLP) formulations. However, these vaccination strategies have specific limitations in manufacturing, immunogenicity, safety, recombination and large scale production. Many, if not all safety problems do not apply for subunit or VLP based vaccines, except for the recombinant origin of the vaccine.

    Recently, a CHIKV VLP-based vaccine was developed and provided protection in both mice and non-human primates. Even though this VLP approach is a safe, efficient and promising alternative to other vaccine strategies, large scale DNA plasmid transfection into mammalian cells and VLP yield of transfected cells remains challenging in terms of industrial production. These problems are alleviated by using the recombinant baculovirus-insect cell expression system.

    In this thesis, recombinant baculoviruses were constructed to produce CHIKV glycoprotein E1 and E2 subunits and VLPs.For the production of CHIKV-E1 and E2 subunits, both protein genes were cloned downstream the polyhedrin gene (polh) promoter of in an Autographica californica multiple nucleopolyhedrovirus backbone, together with their authentic signal peptides 6K(E1) and E3(E2). Deletion of the C-terminal transmembrane domain, generated secreted versions of E1 (E1ΔTM or sE1) and E2 (E2ΔTM or sE2). A substantial amount of recombinant protein was glycosylated and processed by furin. The secreted CHIKV subunits were purified from the medium and were able to induce neutralizing antibodies in rabbits. For the production of the VLPs, the complete structural polyprotein (capsid, E3, E2, 6K, E1) was cloned downstream the AcMNPV polh promoter. E3E2 precursor processing and glycosylation appeared to be more efficient when E3E2 were expressed as part of the whole structural polyprotein cassette, compared to the individually expressed E3E2. The VLPs were isolated from the medium fraction and were morphologically similar to wild type CHIKV. A similar strategy was used to produce VLPs from another alphavirus, the salmonid alphavirus (SAV). Here, however, the normal baculovirus expression temperature of 27°C appeared to be detrimental for SAV-E3E2 furin cleavage and SAV-VLP production. E2-glycoprotein processing was shown to be temperature dependent and a tailored temperature-shift regime was designed in which Sf9-cells were infected with a recombinant baculovirus expressing the SAV structural proteins, and incubated at 27°C for 24 h, followed by a processing phase of 72 h at 15°C. Using this temperature regime, SAV-VLPs were produced that were morphologically indistinguishable from wild type SAV and underscores the flexibility of the baculovirus-insect cell expression system.

    The immunogenicity of purified CHIKV-sE1 and -sE2 subunits and purified CHIKV-VLPs were then tested in a lethal vaccination-challenge mouse model, in IFN α/β, -γ receptor null AG129 mice. The innate immune system of these mice was made dysfunctional. This vaccine-challenge study clearly showed that VLPs provided superior protection, compared to their subunit counterparts. The subunits provided only partial protection and induced low neutralizing antibody titres. Immunization with the VLPs fully protected mice against lethal challenge and induced significant higher neutralizing antibody titress. Even though neutralizing antibody titres were lower after subunit immunization, this study showed that a minor neutralizing antibody response is sufficient to protect mice from lethal CHIKV challenge. Next, the CHIKV VLPs were tested for their ability to induce complete protection in an adult wild-type immune-competent mouse model, in which mice develop arthritic disease after CHIKV infection. The VLPs were able to induce full protection after a single immunization of 1 µg VLPs, without the use of adjuvants. In addition, IgG isotyping revealed a balanced IgG1-IgG2c response, suggesting a role for both humoral and cellular immunity in the protection against CHIKV infection. Mice served as a proxy for primates and vaccination trials in primates are next on the agenda.

    This thesis is a typical example of the opportunities for the recombinant baculovirus-insect cell expression system in viral vaccine development, especially in vaccine development for other arboviruses. Although the CHIKV-VLPs produced in insect cells are amenable for large-scale production, the production process and downstream processing need to be carefully designed and optimized before CHIKV VLPs can be produced on an industrial scale. However, the data presented in this thesis show that CHIKV-VLPs produced in insect cells using recombinant baculoviruses represents as a new, safe, non-replicating and effective vaccine candidate against CHIKV infections.

    Next-generation outer membrane vesicle vaccines from concept to clinical trials
    Waterbeemd, B. van de - \ 2013
    Wageningen University. Promotor(en): Rene Wijffels, co-promotor(en): Michel Eppink. - [S.l.] : s.n. - ISBN 9789461734983
    vaccins - vaccinontwikkeling - neisseria meningitidis - vaccines - vaccine development - neisseria meningitidis

    Only vaccines containing outer membrane vesicles (OMV) have successfully stopped Neisseria meningitidis serogroup B epidemics. The OMV vaccines, however, provide limited coverage and are difficult to produce. This is caused by an obligatory detergent treatment, which removes lipopolysaccharide (LPS), a toxic OMV component. This thesis explored an alternative approach, based on OMV with attenuated lpxL1-LPS and a detergent-free process. The alternative approach is referred to as ‘next-generation OMV’ and provided vaccines with improved immunological and biochemical properties. In addition, quantitative proteomics demonstrated a preferred protein composition. This provided justification for further development towards clinical trials. After optimization of specific process steps, an improved pilot-scale production process was developed. The quality of OMV from this optimized process was stable and within pre-set specifications for nine consecutive batches. Studies in mice and rabbits suggested that next-generation OMV are immunogenic and safe for parenteral use in humans. Therefore these vaccines are now ready for clinical evaluation. Several groups are developing broadly protective OMV vaccines against N. meningitidis serogroup B, but also against other serogroups and other pathogens. OMV therefore have the potential to become a versatile technology platform for prophylactic and therapeutic vaccines. Such a platform requires a reliable production process to generate substantial quantities of high quality product. The process described in this thesis is well-suited for this purpose. The results encourage technology transfer to a commercial partner, with the goal to translate nextgeneration OMV technology into actual vaccines and improve global public health.

    Cell culture based production of avian influenza vaccines
    Wielink, R. van - \ 2012
    Wageningen University. Promotor(en): Rene Wijffels; Rob Moormann, co-promotor(en): Michael Harmsen; Dirk Martens. - S.l. : s.n. - ISBN 9789461733535 - 141
    aviaire influenza - aviaire influenza a-virussen - celcultuur vaccins - vaccins - celkweek - virologie - bioproceskunde - veeartsenijkunde - avian influenza - avian influenza a viruses - cell culture vaccines - vaccines - cell culture - virology - bioprocess engineering - veterinary medicine

    Vaccination of poultry can be used as a tool to control outbreaks of avian influenza, including that of highly pathogenic H5 and H7 strains. Influenza vaccines are traditionally produced in embryonated chicken eggs. Continuous cell lines have been suggested as an alternative substrate to produce influenza vaccines, as they are more robust and lack the long lead times associated with the production of large quantities of embryonated eggs. In the study that is described in this thesis, the production of influenza virus in cell culture was explored. Therefore, several cell lines were assessed for their ability to propagate influenza virus. Furthermore, adaptations to both cell line and seed virus were suggested that increased virus yield, thereby allowing the production of attenuated influenza virus strains.

    Potential introduction of unapproved GM animals and GM products in the Netherlands
    Akker, H.C.M. ; Wassenaar, A.L.M. ; Kleter, G.A. - \ 2012
    Bilthoven : RIVM (RIVM report 09021118/2012)
    siervissen - genetische modificatie - import - inventarisaties - vaccins - gentherapie - internationale handel - ornamental fishes - genetic engineering - imports - inventories - vaccines - gene therapy - international trade
    Het RIVM heeft geïnventariseerd welke genetisch gemodificeerde organismen nu en in de toekomst zouden kunnen worden geïmporteerd, zonder dat daarvoor de benodigde EU-toelating of vergunning is verleend. De afgelopen jaren zijn namelijk varianten van genetisch gemodificeerde siervissen illegaal in de handel gebracht. Het onderzoek heeft zich toegespitst op genetisch gemodificeerde dieren en micro-organismen, die in de Europese Unie nog niet op de markt zijn toegelaten, aangezien een dergelijke inventarisatie voor genetische gemodificeerde gewassen al heeft plaatsgevonden.
    Vaccins beschermen dier én mens
    Rijsman, V.M.C. - \ 2012
    Kennis Online 9 (2012)april. - p. 19 - 19.
    infectieziekten - zoönosen - diergezondheid - volksgezondheid - dierziektepreventie - vaccins - infectious diseases - zoonoses - animal health - public health - animal disease prevention - vaccines
    Het bedrijf MSD Animal Health werkt met onderzoekers van Wageningen UR, het RIVM en de Universiteit Utrecht aan een betere bestrijding van infectieziekten die van dier op mens kunnen overslaan. 'We kunnen nu enkele producten ontwikkelen die mogelijk nooit commercieel aantrekkelijk zullen zijn, maar maatschappelijk wel relevant zijn.'
    Transmission dynamics of Eimeria acervulina in broilers
    Velkers, F.C. - \ 2011
    Wageningen University. Promotor(en): Mart de Jong; J.A. Stegeman, co-promotor(en): A. Bouma. - [S.l.] : S.n. - ISBN 9789085859215 - 153
    vleeskuikens - eimeria acervulina - coccidiose - ziekteoverdracht - experimentele infectie - oöcysten - polymerase-kettingreactie - ziektebestrijding - vaccins - vaccinatie - epidemiologie - broilers - eimeria acervulina - coccidiosis - disease transmission - experimental infection - oocysts - polymerase chain reaction - disease control - vaccines - vaccination - epidemiology

    Control of the intestinal disease coccidiosis, caused by infections with Eimeria species, is a major challenge, especially for the broiler industry. Effective control strategies require a comprehensive understanding of processes that lead to infection and disease in a population. One of the key factors that determine infection dynamics in a flock is the rate of transmission between hosts. Therefore, transmission experiments were carried out to increase the understanding of the underlying mechanisms of Eimeria acervulina infections in broilers, to facilitate improvement of control strategies. An important outcome of the experiments was that the excreted oocyst dose, which may be related to severity of clinical signs, increased during successive generations of infection in the flock, but that the transmission rate was independent of the oocyst dose. This suggests that transmission is not determined by the number of oocysts excreted with faeces of infected birds but, most likely, by the probability of birds to come into contact with infectious faeces. Factors influencing the degree and dispersal of infectious faecal material in the environment, such as movements and (litter pecking) behaviour of chickens, environmental conditions and faeces characteristics, may have a large impact on infection dynamics and efficacy of control measures. Furthermore, it was demonstrated that a previous infection with a wild-type E. acervulina strain significantly reduced oocyst output and transmission after re-infection. After infection with a live vaccine strain, oocyst output following an infection with a wild-type strain was also significantly reduced. However, a significant reduction of transmission of the wild-type strain was not found in groups of broilers that had been infected with the vaccine strain. Nevertheless, it was demonstrated that the live vaccine was efficiently transmitted to initially unvaccinated birds. Furthermore, the level of reduction of oocyst output was equally high for directly vaccinated and the “contact-vaccinated” chickens, that became infected due to ingestion of oocysts excreted by vaccinated birds. These results indicate that transmission of the vaccine can induce protection against high oocyst output for the entire flock, even when not all birds receive the vaccine during the initial mass application. The results of these experiments indicate that influencing the rate of transmission of wild-type and vaccine strains can be important for reducing the adverse effects of flock infections with Eimeria. Furthermore, this thesis has increased insight into some of the underlying factors that determine transmission dynamics of E. acervulina in a broiler flock. Further investigation of these factors may reveal novel targets or facilitate improvement of current strategies for coccidiosis control.

    Innate immune receptors in carp: recognition of protozoan parasites
    Ribeiro, C.M.S. - \ 2010
    Wageningen University. Promotor(en): Huub Savelkoul, co-promotor(en): Geert Wiegertjes. - [S.l. : S.n. - ISBN 9789085857747 - 217
    karper - immuniteitsreactie - receptoren - protozoa - parasieten - immuunsysteem - vaccins - hulpstoffen - immunologie - immuniteit - carp - immune response - receptors - protozoa - parasites - immune system - vaccines - adjuvants - immunology - immunity
    This PhD thesis reports on pattern recognition receptors involved in the immune responses of common carp (Cyprinus carpio) to two protozoan parasites Trypanoplasma borreli and Trypanosoma carassii. The immune responses of carp are fundamentally different when comparing these two extracellular blood parasites. T. borreli induces a characteristically high production of nitric oxide by macrophages, whereas T. carassii parasites seem to preferentially induce an alternative state of macrophage activation. These differences could be driven by differences in the initial engagement of pattern recognition receptors on carp macrophages with either of the two types of parasites. Based on known host-parasite interactions in mammalian vertebrates, Toll-like receptor 2 (TLR2) and TLR9 were selected as candidate receptors for parasite recognition by receptors carp macrophages. Transfection of human cell cultures with carp TLR2 and overexpression of TLR2 in carp macrophages, corroborated the ability of this receptor to bind peptidoglycan from Gram-positive bacteria and glycosylphosphatidylinositol anchors from protozoan parasites. The parasite T. carassii, in particular, induced a TLR2-mediated formation of the cytokine IL-23, leading to a Th17-like immune response in fish infected with T. carassii. Transfection of human cell cultures with carp TLR9 indicated this receptor recognizes bacterial DNA, but not protozoan DNA, and studies in carp macrophages indicated this recognition to be protease-dependent. A novel pattern recognition receptor of carp, named Soluble Immune-Type Receptor (SITR), was identified by investigating an enriched cDNA repertoire from macrophages stimulated by T. borreli. SITR is abundantly expressed in carp macrophages and seems to be secreted upon stimulation with T. borreli. Overexpression of SITR in mouse macrophages and knock-down of SITR in carp macrophages provided evidence for the involvement of this receptor in T. borreli-induced production of nitric oxide. The results presented in this PhD thesis have shed light on the evolution of innate immune receptors involved in the recognition of pathogens.
    Development of an influenza virus vaccine using the baculovirus-insect cell expression system : implications for pandemic preparedness
    Cox, M.M.J. - \ 2009
    Wageningen University. Promotor(en): Just Vlak, co-promotor(en): Monique van Oers. - [S.l. : S.n. - ISBN 9789085854791 - 135
    vaccinontwikkeling - vaccins - influenza - baculovirus - insecten - hemagglutininen - celcultuur vaccins - recombinant vaccins - vaccine development - vaccines - influenza - baculovirus - insects - haemagglutinins - cell culture vaccines - recombinant vaccines
    Key word

    Influenza, rHA, vaccine, baculovirus, insect cells, production, pandemic preparedness

    Influenza (or flu) is a highly contagious, acute viral respiratory disease that occurs seasonally in most parts of the world and is caused by influenza viruses. Influenza vaccination is an effective way to reduce the complications and the mortality rate following influenza infections. The currently available influenza vaccines are manufactured in embryonated chicken eggs, a 40-year old production technology. The research in this thesis was aimed at the design, validation and development of a production process for a recombinant hemagglutinin (rHA) influenza vaccine for the prevention of seasonal influenza. The viral surface protein HA is the key antigen in the host response to influenza virus since neutralizing antibodies directed against HA can mitigate or prevent infection. The baculovirus-insect cell system was selected for the synthesis of rHA molecules. The designed process was used to manufacture candidate trivalent rHA vaccines, which were tested in four clinical studies in a total of more than 3000 human subjects age 18 - 92 to support licensure of FluBlok under the “Accelerated Approval” procedure in the United States (U.S.). These studies demonstrated that the purified rHA protein was well tolerated and resulted in a strong and long lasting immune response. In addition, the novel vaccine provided cross protection against drifted influenza viruses. In response to the emergence of the new H1N1 A/California /04/2009 influenza strain, the outlined design was used to produce a rHA vaccine candidate and merely 6 weeks later, the first batches of vaccine were ready for human clinical testing. There are two especially important advantages to the use of this technology from a public health perspective: First, the insect cell-baculovirus system has demonstrated the potential to facilitate safe and expeditious responses to health care emergencies such as the one currently posed by the novel H1N1 virus pandemic and secondly, the rHA vaccine does not contain ovalbumin or other antigenic proteins that are present in eggs and may therefore be administered to people who are egg-allergic.


    Immuuninterventie : 'Drukken op de juiste knoppen van het afweersysteem'
    Schijns, V.E.J.C. - \ 2009
    Wageningen : Wageningen Universiteit - ISBN 9789085852773 - 32
    immunologie - immuniteitsreactie - immuniteit - immuunsysteem - immunisatie - vaccins - vaccinatie - immunology - immune response - immunity - immune system - immunization - vaccines - vaccination
    Nieuw vaccin tegen campylobacter
    Wagenaar, J.A. - \ 2008
    Kennis Online 5 (2008)dec. - p. 9 - 9.
    campylobacter - vaccins - kippen - voedselveiligheid - campylobacter - vaccines - fowls - food safety
    Het vaccin dat de kip moet beschermen tegen de bacterie Campylobacter werkt in het laboratorium. Dat wil bacterioloog Jaap Wagenaar wel kwijt. Wanneer het er komt en zelfs of het er komt, daarover laat Wagenaar zich niet uit. "Het is een hele klus om het immuunsysteem van kippen effectief op te laten treden tegen Campylobacter", zegt Wagenaar die werkt bij het CVI en hoogleraar is aan de Universiteit Utrecht. "Geen van de vaccins die onderzoekers tot nu hebben uitgeprobeerd werken"
    Whooping cough vaccines: production of virulent B. pertussis
    Thalen, M. - \ 2008
    Wageningen University. Promotor(en): Hans Tramper, co-promotor(en): Dirk Martens; T.W. Graaf. - S.l. : S.n. - ISBN 9789085049531 - 149
    kinkhoest - bordetella pertussis - vaccins - vaccinontwikkeling - biologische productie - bioreactoren - kweekmedia - pertussis - bordetella pertussis - vaccines - vaccine development - biological production - bioreactors - culture media
    key words: acellular, fed batch, metabolism, pertussis toxin

    The production of acellular pertussis in comparison with whole cell pertussis
    vaccines demands 5 to 25 times the amount of B. pertussis' virulence factors such
    as pertussis toxin (PT), to produce the same number of vaccine doses. An
    increase in the volumetric productivity by employing fed-batch rather than the
    currently used batch cultivations of B. pertussis could reduce the cost price of
    acellular pertussis vaccines. This study defined the conditions that enable fed
    batch cultivations at high specific PT production. A solution containing lactate and
    glutamate was fed to the cultures at various rates. The feed rate and whether or
    not the fed substrates were completely consumed, significantly influenced cellular
    metabolism. If lactate was detectable in the culture broth while glutamate was not,
    poly-hydroxy-butyrate (PHB) was formed. Any PHB present was metabolized
    when glutamate became detectable again in the culture liquid. At higher lactate
    and glutamate concentrations, free fatty acids were produced. Though toxic, free
    fatty acids were not the reason cultures stopped growing. By choosing appropriate
    conditions, a cell density of 6.5 g.L-1 dry weight was reached, i.e. a 7-fold increase
    compared to batch culture. The metabolic mechanisms behind the formation of
    PHB and fatty acids are discussed, as well as how to further increase the cell
    density. The PT production stopped at 12 mg.L-1, well before growth stopped,
    indicating that regulatory mechanisms of PT production may be involved.
    Questionnaire survey of disease prevalence and veterinary treatments in organic layer husbandry in the Netherlands
    Meulen, J. van der; Werf, J.T.N. van der; Kijlstra, A. - \ 2007
    Tijdschrift voor Diergeneeskunde 132 (2007)8. - ISSN 0040-7453 - p. 292 - 295.
    biologische landbouw - veterinaire producten - kippenziekten - ziektedistributie - uitbraken (ziekten) - epidemiologie - veterinaire praktijk - kippen - vaccins - vaccinatie - homeopathische geneesmiddelen - fytochemicaliën - vragenlijsten - epidemiologische onderzoeken - dierziektepreventie - organic farming - veterinary products - fowl diseases - disease distribution - outbreaks - epidemiology - veterinary practice - fowls - vaccines - vaccination - homeopathic drugs - phytochemicals - questionnaires - epidemiological surveys - animal disease prevention - animal health - livestock production - welfare - systems - europe - hens
    Disease prevalence and veterinary treatments in organic animal production differ from those in conventional systems. In order to gather information about current current practices in organic layer husbandry, 33 organic egg producers of 16 small, 12 medium-sized and 5 large farms were asked to complete a questionnaire on disease prevalence and treatments. On these farms, the mean mortality was 9% and the mean laying percentage was 79%. In contrast with the regulations for organic farming, the use of chemotherapeutics was not recorded on 30% of the farms. One third of the farmers were not aware of the type of vaccination given to their hens, and on the other farms hens had been vaccinated as pullets against nine or more viral and bacterial diseases. Several health problems were mentioned, such as feather pecking, red mites, helminthes, infectious bronchitis, colibacillosis and coccidiosis. On 19 farms, diseases were treated with homeopathic, phytotherapeutic, or other alternative medicines; on 10 of these farms chemotherapeutics were also used. Although quite a large number of organic layer farmers in the Netherlands used homeopathic, phytotherapeutics or other alternative medicines, the use of chemotherapeutics is currently inevitable to prevent animal suffering or distress in organic husbandry
    Disease prevalence and veterinary treatments in organic animal production differ from those in conventional systems. In order to gather information about current practices in organic layer husbandry, 33 organic egg producers of 16 small, 12 medium-sized, and 5 large farms were asked to complete a questionnaire on disease prevalence and treatments. On these farms, the mean mortality was 9% and the mean laying percentage was 79%. In contrast with the regulations for organic farming, the use of chemotherapeutics was not recorded on 30% of the farms. One third of the farmers were not aware of the type of vaccination given to their hens, and on the other farms hens had been vaccinated as pullets against nine or more viral and bacterial diseases. Several health problems were mentioned, such as feather pecking, red mites, helminths, infectious bronchitis, colibacillosis, and coccidiosis. On 19 farms, diseases were treated with homeopathic, phyto-therapeutic, or other alternative medicines; on 10 of these farms chemotherapeutics were also used. On 4 farms only chemotherapeutics were used, on 10 farms no products were used, and on some farms up to seven products were used. Although quite a large number of organic layer farmers in the Netherlands used homeopathic, phytotherapeutic, or other alternative medicines, the use of chemotherapeutics is currently inevitable to prevent animal suffering or distress in organic husbandry.
    Afzet vlees van gevaccineerde varkens : een verkenning van economische consequenties
    Hoste, R. ; Bergevoet, R.H.M. - \ 2007
    Den Haag : LEI (Rapport / LEI : Domein 2, Bedrijfsontwikkeling en concurrentiepositie ) - ISBN 9789086151448 - 31
    agrarische economie - vlees - slachtdieren - varkens - varkensvlees - dierziekten - varkensziekten - vaccins - vaccinatie - agricultural economics - meat - meat animals - pigs - pigmeat - animal diseases - swine diseases - vaccines - vaccination
    Bij uitbraken van dierziekten willen overheid en sector niet langer grote aantallen dieren doden, maar gericht vaccineren. Om vlees van gevaccineerde varkens af te kunnen zetten, moet dit vlees gekanaliseerd worden. In deze verkennende studie zijn economische consequenties onderzocht van kanaliseren en beperking van het afzetassortiment bij verschillende aanbodvolumes van vlees van gevaccineerde varkens. De kosten hangen samen met het volume en het gekozen afzetkanaal en variëren tussen ¿ 0,60 en ¿ 1,69 per kg vlees
    BVD-approach: prevention by Mr. L.R.M. Verberne = Reactie op ingezonden brief in het Tijdschrift voor Diergeneeskunde van 15 augustus 2005: BVD-aanpak: preventie van de heer L.R.M. Verberne
    Antonis, A.F.G. ; Poel, W.H.M. van der - \ 2005
    Tijdschrift voor Diergeneeskunde 130 (2005)17. - ISSN 0040-7453 - p. 530 - 530.
    veehouderij - virusziekten - pestivirus - ziektepreventie - ziektebestrijding - antilichamen - infectie - vaccinatie - vaccins - dierziektepreventie - kritiek - livestock farming - viral diseases - disease prevention - disease control - antibodies - infection - vaccination - vaccines - animal disease prevention - criticism
    Een reactie op het artikel 'BVD-aanpak: preventie' in tijdschrift voor Diergeneeskunde 130(2005)nr. 16, waarin gesteld wordt dat op een rundveebedrijf alle of nagenoeg alle dieren dienen te beschikken over afweerstoffen tegen het BVD-virus om schade door besmetting te voorkomen. De reactie geeft aan dat dit onnauwkeurig is verwoord
    Appraisal of the Epidemiology of Neospora caninum Infection in Costa Rican Dairy Cattle
    Romero Zúñiga, J.J. - \ 2005
    Wageningen University. Promotor(en): Mart de Jong, co-promotor(en): Klaas Frankena; E. Pérez Gutiérrez. - [S.l.] : S.n. - ISBN 9789085042709 - 137
    melkkoeien - melkveestapel - neospora caninum - neosporose - melkresultaten - voortplanting - abortus - vaccins - epidemiologie - costa rica - dairy cows - dairy herds - neospora caninum - neosporosis - dairy performance - reproduction - abortion - vaccines - epidemiology - costa rica
    Costa Rica, milk production has increased gradually during the twentieth century, in which the activity developed from a non-technical to a technical activity. Together with the evolution of the dairy sector, the incidence of infectious and metabolic diseases increased, leading to increased economic losses. According to a VAMPP data base, the global percentage of abortion during the period between 1988 and 2003 varied between 7.5 and 12%; but at individual farms abortion rates close to 30% occurred in one or more years. Abortion is one of the most important economic disorders.Since the 90´sneosporosis( N.caninum ) has been associated with abortion andfoetallosses in cattle all over the world.In 1996, a study stated (for the first time) the presence ofneosporosisinCosta Ricaand N.caninum was diagnosed (Perez et al., 1998).The aim of this thesis is to describe the most important features ofneosporosisin Costa Rican dairy cattle in order to develop strategies for the prevention and control of the infection. The main results of this thesis are: 1)no significant effects ofNeosporaserostatuswere detected on (re)productive performance; 2) theassociation between management and environmental factors withserostatuswas found to be absent3) in the specific conditions of the dairy herds involved in this study, theserostatusof the cows should be not used as predictor of theserostatusof daughters due to the high probability of horizontal transmission, 4) the killed wholeNeosporacaninumtachyzoitepreparation reduced the abortion rate in Costa Rican dairy cattle.
    Streptococcus suis infections in pigs: use of virulence-associated markers in diagnostics and vaccines = Streptococcus suis infecties bij varkens: het gebruik van virulentiekenmerken in diagnostiek en vaccins
    Wisselink, H.J. - \ 2001
    - 146
    varkens - streptococcus suis - ziektemerkers - vaccins - pigs - streptococcus suis - disease markers - vaccines
    Streptococcus suis is an important pig pathogen which is mainly associated with meningitis, arthritis and septicaemia. Control of the disease is hampered by the lack of effective vaccines and the lack of reliable diagnostic tests with high specificity and sensitivity. The development of these tools is complicated by the number of existing serotypes, by the fact that we still lack knowledge of the factors responsible for virulence and protection, and by the fact that strains may vary in virulence. Therefore, research focused on the identification of virulence-associated markers that discriminate between virulent and less virulent or avirulent isolates, has gained considerable interest in recent years. The aim of the investigations described in this thesis, was to test whether these virulence-associated markers could be used in diagnostic assays for the detection of S. suis infections and/or for use in vaccines to protect against the disease. In previous work, muramidase-released protein (MRP) and extracellular-factor protein EF were identified as markers of virulence in serotype 1 and 2 strains. In other serotypes the production of MRP and EF, and their potential importance for bacterial virulence has not been investigated. Therefore, we determined the serotypes as well as MRP and EF phenotypes for a collection of S. suis strains isolated from diseased pigs in seven European countries. Overall, S. suis serotype 2 appeared to be most prevalent (32Œ followed by serotype 9 (20€and serotype 1 (12Ž EF-positive strains, were found in serotype 1 (66Œ 2 (71€and 14 (85€strains. Variants of MRP (MRP* or MRPs) were found in nearly all serotypes. A high percentage (81€of the serotype 9 strains belonged to the MRP*EF- phenotype. For the detection of pigs carrying virulent serotype 2 strains, serotype 1, 1/2, 7, 9 and 14 strains, Multiplex PCR tests have been developed. In Multiplex PCR 1, three DNA targets, based on the S. suis serotype 1 (and 14), 7 and 9 specific capsular polysaccharide (cps) genes, were amplified. In Multiplex PCR II, two other targets, based on the serotype 2 (and 1/2) specific cps gene and the epf gene encoding the EF-protein, were amplified. The evaluation of these PCRs for use on tonsillar specimens of diseased pigs demonstrated that the assays were highly specific and sensitive. For the development of protective vaccines, the efficacy of a MRP and EF vaccine applied in pigs was tested. Pigs were vaccinated twice and challenged intravenously with virulent S. suis serotype 2 strains. At challenge, pigs vaccinated with MRP and EF were protected against infection and disease. Pigs vaccinated with either MRP or EF were less well protected. Apparently the combination of both proteins is necessary to obtain full protection. The protective efficacy of an avirulent, non-encapsulated isogenic mutant of S. suis serotype 2 was determined in pigs, and compared with the efficacy of the capsulated wild-type strain. Vaccinations were with formalin-killed cells of the wild-type (WT-BAC), formalin-killed cells of the non-encapsulated mutant (CM-BAC) or with the live non-encapsulated mutant (CM-LIVE) strain. Pigs were challenged intravenously with the homologous, wild-type S. suis serotype 2 strain. The results demonstrated that, as expected, the formalin-killed cells of WT-BAC induced complete protection in pigs against mortality and morbidity after challenge. The formalin-killed cells of CM-BAC induced complete protection against mortality, but only partial protection against morbidity. The CM-LIVE vaccine induced only partial protection, both against mortality and morbidity. These findings indicate that CPS and other bacterial components of WT-BAC are probably essential for full protection against homologous challenge.
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