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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    The role of Culex pipiens mosquitoes in transmission of West Nile virus in Europe
    Vogels, Chantal B.F. - \ 2017
    Wageningen University. Promotor(en): M. Dicke, co-promotor(en): C.J.M. Koenraadt. - Wageningen : Wageningen University - ISBN 9789463436151 - 211
    culex pipiens - mosquito-borne diseases - west nile virus - disease transmission - disease vectors - vector-borne diseases - europe - culex pipiens - 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.

    Microorganism-mediated behaviour of malaria mosquitoes
    Busula, Annette O. - \ 2017
    Wageningen University. Promotor(en): W. Takken, co-promotor(en): J. de Boer. - Wageningen : Wageningen University - ISBN 9789463431156 - 199
    culicidae - anopheles gambiae - anopheles arabiensis - mosquito-borne diseases - disease vectors - animal behaviour - host-seeking behaviour - plasmodium falciparum - hosts - man - cows - hens - odours - culicidae - anopheles gambiae - anopheles arabiensis - ziekten overgebracht door muskieten - vectoren, ziekten - diergedrag - gedrag bij zoeken van een gastheer - plasmodium falciparum - gastheren (dieren, mensen, planten) - mens - koeien - hennen - geurstoffen

    Host-seeking is an important component of mosquito vectorial capacity on which the success of the other behavioural determinants depends. Blood-seeking mosquitoes are mainly guided by chemical cues released by their blood hosts. This thesis describes results of a study that determined the effect of microorganisms – host skin bacteria as well as malaria parasites – on host-seeking behaviour of female Anopheles gambiae sensu stricto and An. arabiensis in Homabay county, western Kenya. Semi-field and field experiments were conducted to determine the response of mosquitoes with different host preference to synthetic and natural odour blends from three vertebrate hosts, a human, a cow and a chicken. Screen house experiments were conducted to test whether specific skin bacteria or a mix of skin bacterial volatiles from the three vertebrate hosts mediate mosquito response. A review chapter in this thesis discusses how malaria parasites can manipulate human hosts to enhance their own transmission, by making the hosts more attractive to mosquitoes. Another experiment, using a dual-choice olfactometer, determined whether infection with malaria parasites increases human attractiveness to malaria mosquitoes, and whether the attractiveness of infected humans is Plasmodium falciparum-stage specific. Here, the same children participated in the study during infection with malaria parasites and after treatment with antimalarial drugs, artemisinin lumefantrine. Cage assays were further used to test mechanisms of attractiveness of P. falciparum-infected individuals using body odours or skin bacterial volatiles collected from the children at the two time points. Overall results show that skin bacterial volatiles play an important role in guiding mosquitoes with different host preferences to their specific host. For An. gambiae s.s., high (microscopic) densities of P. falciparum gametocytes (and not parasite-free, submicroscopic gametocytes or asexual stages of Plasmodium parasites) results into higher attractiveness of hosts, and body odours play a role in attractiveness of P. falciparum-infected humans. The results may help to develop more effective health policies and enable targeted interventions towards the most attractive hosts, which could contribute to reductions in malaria transmission. Identification of general or common attractive volatiles produced by the natural hosts as well as those from the gametocyte carriers may contribute to the development of an improved synthetic odour blend that may be used for sampling of mosquitoes with different host preferences. The use of powerful attractive odorants may result in reductions of vector-borne diseases transmitted by mosquitoes.

    The ecology of Lyme borreliosis risk : interactions between lxodes ricinus, rodents and Borrelia burgdorferi sensu lato
    Duijvendijk, Gilian van - \ 2016
    Wageningen University. Promotor(en): Willem Takken, co-promotor(en): H. Sprong. - Wageningen : Wageningen University - ISBN 9789462579408 - 186
    rodents - ixodes ricinus - disease vectors - tickborne diseases - borrelia burgdorferi - borrelia miyamotoi - hosts - ecological risk assessment - risk analysis - knaagdieren - ixodes ricinus - vectoren, ziekten - ziekten overgebracht door teken - borrelia burgdorferi - borrelia miyamotoi - gastheren (dieren, mensen, planten) - ecologische risicoschatting - risicoanalyse

    The sheep tick (Ixodes ricinus) is widespread throughout Europe and can transmit Borrelia burgdorferi sensu lato (s.l.), which can cause Lyme borreliosis and B. miyamotoi, the agent of Borrelia miyamotoi disease in humans. Borrelia afzelii is the most common genospecies of Borrelia burgdorferi s.l. in western Europe and it circulates between I. ricinus and rodents. The density of infected nymphs determines disease risk and is affected by complex multi-trophic interactions between factors that are not well understood. The aim of this thesis was, therefore, to gain insight into the multi-trophic interactions that affect the density of B. afzelii-infected and B. miyamotoi-infected I. ricinus nymphs.

    Interactions between I. ricinus, rodents (wood mice and bank voles) and B. afzelii were reviewed to elucidate knowledge gaps concerning these interactions. The effect of rodent density on the density of infected nymphs and the factors that affect the contribution of a rodent to the density of infected nymphs were investigated in field experiments. The effects of a B. afzelii infection on larval tick burden of bank voles and nymphal body weight were investigated in the laboratory. The effects of CO2 and host odour on the host-seeking behaviour of I. ricinus were investigated in a Y-tube olfactometer. Finally, the ability of field-collected I. ricinus larvae to transmit B. afzelii and B. miyamotoi was analysed.

    The review showed that rodent density, rodent infection rate, and larval tick burden are the major factors affecting the density of B. afzelii-infected nymphs one year later. The field experiments showed that rodent density can positively affect the density of B. burgdorferi s.l.- infected nymphs one year later. However, the effect of rodent density was small when the density of infected nymphs was limited by the density of questing larvae in the previous year. Rodent density had, however, no effect on the density of B. miyamotoi-infected nymphs. The field studies also showed that tick burdens are 2.4 times higher on wood mice than on bank voles and that body weight of emerged nymphs was 36% higher for ticks that fed on wood mice compared to ticks that fed on bank voles. Bank voles infected with B. afzelii acquired a larger larval tick burden, resulting in a 27% increase in nymphal infection prevalence. Furthermore, infected nymphs had a 10% greater the body weight. Ixodes ricinus nymphs are activated by but not attracted to CO2, whereas they are attracted to and not activated by host odour. Ixodes ricinus larvae transmitted both B. afzelii and B. miyamotoi to rodents and it was calculated that rodents have a chance of about 25-75% of acquiring B. afzelii from larvae relative to the chance of acquiring B. afzelii from nymphs. The main conclusions of this thesis are discussed and suggestions are made for future research.

    The wild life of tick-borne pathogens
    Hofmeester, Tim R. - \ 2016
    Wageningen University. Promotor(en): Herbert Prins, co-promotor(en): Sip van Wieren. - Wageningen : Wageningen University - ISBN 9789462579699 - 224
    ixodes ricinus - metastigmata - life cycle - tickborne diseases - disease vectors - mammals - birds - hosts - population ecology - tick infestations - host parasite relationships - ixodes ricinus - metastigmata - levenscyclus - ziekten overgebracht door teken - vectoren, ziekten - zoogdieren - vogels - gastheren (dieren, mensen, planten) - populatie-ecologie - tekenbesmettingen - gastheer parasiet relaties

    Diseases that are transmitted by arthropod vectors from animal hosts to humans – so called zoonotic vector-borne diseases – have increased in incidence in the last decades. In North America and Europe, tick-borne pathogens cause the majority of vector-borne diseases, including Lyme borreliosis and tick-borne encephalitis. The pathogens causing these diseases are transmitted by tick species within the Ixodes ricinus complex. These are generalist ticks that have a multi-year lifecycle with three active stages, larva, nymph and adult. Each stage passively waits for a vertebrate host by questing in the vegetation. Once a host is encountered these ticks feed on the host for several days sucking blood, after which they detach and moult to the next stage or lay eggs. Although these ticks spend the majority of their life in the vegetation, the availability of hosts is an important determinant of tick densities.

    In Europe, the Sheep tick (Ixodes ricinus) is the most important vector for tick-borne pathogens. These pathogens include Borrelia burgdorferi sensu lato (s.l.), the causative agent of Lyme borreliosis, Anaplasma phagocytophilum, the causative agent of human granulocytic anaplasmosis, Borrelia miyamotoi, the causative agent of acute febrile illness and Candidatus Neoehrlichia mikurensis, the causative agent of neoehrlichiosis. There are several genospecies within the B. burgdorferi s.l. complex, among which B. afzelii, B. bavariensis, B. garinii, B. lusitaniae, B. spielmanii, and B. valaisiana are found in questing ticks and patients in the Netherlands. All of these pathogens are maintained and amplified by vertebrate hosts. Host species differ in their ability to transmit the different pathogens (reservoir competence), as well as in their competence for ticks. Therefore, it has been hypothesized that changes in vertebrate assemblage composition can change tick-borne pathogen dynamics and thereby tick-borne disease risk, where a decrease in host species diversity might lead to an increased disease risk, the so-called dilution effect of host species richness hypothesis.

    In his thesis, Tim Hofmeester describes his research on the role of different vertebrate host species in maintaining I. ricinus populations and in infecting I. ricinus larvae with different tick-borne pathogens. By performing a systematic review, Hofmeester found that for both mammals and birds, there was a positive correlation between host body mass and tick burden for the different stages. Nymphal burden was positively correlated with infection prevalence with B. burgdorferi s.l. in hosts, which was again positively correlated with the average number of larvae that got infected with B. burgdorferi s.l. while feeding on a host. He also showed that the majority of I. ricinus individuals of the three stages (larva, nymph and adult) feed on only a few vertebrate host species (rodents, thrushes and deer, respectively). Using camera traps, Hofmeester showed that the presence of deer, such as Roe deer and Red deer, was a more important determinant of I. ricinus density than the number of deer available to ticks in twenty forested areas in the Netherlands. Ixodes ricinus densities were significantly reduced after two years of excluding deer by fencing four 0.75 ha forest plots in a forest near Apeldoorn, the Netherlands. Therefore, tick-borne disease risk can be reduced by placing fences around small forested areas with a high recreational pressure.

    Hofmeester showed that tick burdens on rodents were higher in areas with large numbers of deer, while they were lower in areas with large numbers of carnivores. These differences in tick burden on rodents between areas were strongly correlated to the number of questing nymphs in the vegetation that were infected with tick-borne pathogens that are transmitted by rodents. This implies that changes in vertebrate assemblage can lead to cascading effects on rodent-transmitted tick-borne disease risk, via larval burden on rodents. Furthermore, Hofmeester found that the percentage of ticks infected with a specific pathogen was correlated to the number of animals in an area that could transmit this pathogen, while this percentage decreased with the number of animals that could not transmit this pathogen. These parameters were, however, not correlated to species richness, something that was expected based on the dilution effect of species richness hypothesis. Therefore, there is no support for a dilution effect of species richness on tick-borne pathogens in the Netherlands.

    In his synthesis, Hofmeester presents a mathematical model in which the importance of spatial behaviour of hosts for tick-borne pathogens is shown and he proclaims the need for the integration of the field of behavioural ecology into disease ecology to better understand the effect of changes in vertebrate assemblages on pathogen prevalence and ultimately, disease risk. The data presented in this thesis show that it is not host diversity but the presence, abundance and behaviour of specific host species that drives tick-borne pathogen dynamics (identity effect). Vertebrate species change their behaviour in the presence or absence of predators and competitors. Hofmeester shows that this, theoretically, can have a major influence on the density of infected nymphs in the vegetation. Therefore, behavioural changes of reservoir-competent hosts should be taken into account when modelling the effect of changes in vertebrate assemblage composition on tick-borne disease risk.

    The behaviour of vertebrate species in Europe is changing, as multiple species have adapted to human-dominated and fragmented landscapes. The adaptation of small mammals, thrushes and deer to fragmented landscapes might be one of the driving factors behind the increase in tick-borne disease incidence in Europe. A further adaptation of important host species to urbanized landscapes might be expected as these are the safest areas for vertebrate species trying to avoid predation. This might result in an increase in population density of reservoir-competent host species in urban areas with a corresponding increase in tick-borne pathogen prevalence and therefore, tick-borne disease risk.

    Concluding, our world is changing and as a consequence vertebrate assemblages are also changing. This may lead to changes in I. ricinus density and infection prevalence with tick-borne pathogens. From the studies presented in his thesis Hofmeester concludes that the abundance and behaviour of several host species (e.g., Bank vole, Blackbird, Red deer, Red fox, Roe deer, and Wood mouse) determines tick-borne disease risk. Therefore, studying the drivers of animal abundance and behaviour related to ticks and pathogens will be the next step in better understanding and describing tick-borne disease risk. The ecology of tick-borne pathogens is very complex and targeting vertebrate hosts for intervention strategies will be both inefficient and costly due to the intricate interplay between multiple vertebrate host species. Therefore, Hofmeester concludes that prevention of tick bites is the best way to reduce tick-borne disease incidence.

    Maintenance of Borrelia burgdorferi s.l. diversity in enzootic cycles
    Swart-Coipan, Elena - \ 2016
    Wageningen University. Promotor(en): Willem Takken; Herbert Prins, co-promotor(en): H. Sprong. - Wageningen : Wageningen University - ISBN 9789462579576 - 180
    borrelia burgdorferi - life cycle - tickborne diseases - metastigmata - ixodes ricinus - disease vectors - rodents - mammals - genetic analysis - multilocus sequence typing - lyme disease - borrelia burgdorferi - levenscyclus - ziekten overgebracht door teken - metastigmata - ixodes ricinus - vectoren, ziekten - knaagdieren - zoogdieren - genetische analyse - multi-locus sequentie typering - lyme-ziekte

    Lyme borreliosis is the most prevalent vector-borne disease in the temperate regions of the northern hemisphere. The bacteria that cause it are members of the Borrelia burgdorferi sensu lato complex, a group of spirochaetes which are transmitted by hard ticks of the Ixodes ricinus complex. In several European countries, including The Netherlands, the incidence of Lyme borreliosis has been on the rise for the last decades. The acarological risk of human infection with Borrelia burgdorferi s.l. has been defined as the density of infected questing nymphs. This definition assumes that the distribution of the various genospecies of Borrelia in Lyme borreliosis is reflected in their distribution in questing ticks; furthermore, it assumes that all Borrelia genospecies are considered equally hazardous for humans. In order to define effective intervention strategies for controlling the disease, more insight in the transmission dynamics of tick-borne pathogens, both between animals and ticks, but also from ticks to humans is needed. As part of a Dutch research programme – “Shooting the messenger” – this PhD thesis focussed on linking the transmission cycles of Lyme spirochaetes to the different clinical manifestations of Lyme borreliosis. To that end, I explored aspects of the ecology and molecular adaptations of B. burgdorferi s.l. at various scales, from complex to genospecies level.

    The ecological adaptations of B. burgdorferi s.l. are underpinned by a complex genomic structure and gene expression, with large genetic variation among and within the genospecies. In Chapter 3, we prove that the 5S-23S rDNA intergenic spacer (IGS) is a suitable molecular marker for identification of B. burgdorferi s.l. to genospecies level, but also to characterize the genetic diversity at intragenospecies level and to detect genetic differentiation among the subpopulations of Borrelia. Consequently, we used this marker in combination with other genetic markers, in the studies addressing the genetic diversity of Borrelia in small mammals and humans.

    The main transmission route of these bacteria is the interstadial one, from larvae to nymphs and from nymphs to adult ticks. Larvae of I. ricinus can become infected during a blood meal from an infected host and during a blood meal in the vicinity of an infected nymph feeding on a host, a process known as co-feeding. The infected engorged larvae then moult into infected nymphs, which can transmit the spirochaetes to new hosts. The same process is repeated in the next developmental stage – nymph to adult. Thus, the maintenance of the bacteria in enzootic cycles is dependent on various species of vertebrates and the ticks that feed on them. In order to identify the main vertebrate hosts responsible for the maintenance of B. burgdorferi in enzootic cycles, but also for feeding I. ricinus ticks, we conducted a meta-analysis on literature data (Chapter 2). Our quantification method suggests that only a few host species, which are amongst the most widespread species in the environment (rodents, thrushes and deer), feed the majority of I. ricinus individuals and that rodents infect the majority of I. ricinus larvae with B. burgdorferi s.l.. The increase in distribution and abundance of these species, could be one of the main causes for the increase in Lyme borreliosis incidence in Europe in recent decades.

    While at genospecies level, there is host specificity, with B. afzelii associated with rodents and B. garinii with birds, we wanted to see if the same holds true at intragenospecies level, for the various genotypes of Borrelia. Chapter 4 focuses on the rodents, which were identified in the literature meta-analysis as being the main hosts for I. ricinus larvae as well as for Borrelia afzelii. We tested the multiple niche polymorphisms hypothesis, using IGS, dbpA and ospC as molecular markers for typing B. afzelii genotypes in fed larvae collected from rodents in various areas in The Netherlands. Despite the high genetic diversity within B. afzelii, there was no difference between wood mice and bank voles in the number and types of B. afzelii haplotypes they transmit. Additionally, we compared the quantitative role of bank voles and wood mice in B. afzelii and Neoehrlichia mikurensis maintenance, another emerging tick-borne pathogen in Europe. Neoehrlichia mikurensis prevalence was positively associated with B. afzelii. Mathematical models including tick burden and infection prevalence indicated that bank voles are better amplifiers of these two bacteria than wood mice. Our study suggests that wood mice and bank voles differ in their contribution to the dynamics of B. afzelii, and possibly other TBP, in questing ticks but not in their contribution to the genetic diversity of these microorganisms.

    The density of the vertebrate hosts and the feeding preferences of the ticks should determine the prevalence of B. burgdorferi s.l. genospecies in questing ticks. We address this topic in Chapter 5, by testing 5,570 questing I. ricinus nymphs from 22 different areas in The Netherlands. We found an overall prevalence of 11.8% for B. burgdorferi s.l., with large and consistent variations among the various locations. As expected based on the results of Chapter 2, Borrelia afzelii was predominant (6.7 % of the questing ticks) among the B. burgdorferi s.l. genospecies. It was followed by B. garinii/B. bavariensis (1.5 %), B. valaisiana (1.2 %), and B. burgdorferi sensu stricto (0.2 %). We noticed that, over the usual range of questing ticks’ densities, the density of infected ticks is increasing with the overall density of questing ticks, and a downward trend might be observed only for questing tick densities of over 200/100 m2. This indicates that the density of questing nymphs is the main driver of the acarological risk of human exposure to B. burgdorferi s.l.

    We also screened for the presence of other tick-borne pathogens that have previously been detected in questing ticks in The Netherlands: Rickettsia helvetica, Anaplasma phagocytophilum, Neoehrlichia mikurensis and several Babesia spp. (Chapter 5). To test whether these pathogens might share similar enzootic cycles we looked for patterns of coinfection and seasonal dynamics of infection in questing I. ricinus nymphs. One-third of the Borrelia-positive ticks were infected with at least one other pathogen. Coinfection of B. afzelii with N. mikurensis and with Babesia spp. occurred significantly more often than single infections, indicating the existence of mutual reservoir hosts. The diversity of tick-borne pathogens detected in I. ricinus in this study and the frequency of their coinfections with B. burgdorferi s.l. underline the need to consider them when evaluating the risks of infection and subsequently the risk of disease following a tick bite.

    Chapter 6 addresses the pathogenicity of B. burgdorferi s.l. genospecies and genotypes for humans, using the eight multilocus sequence typing scheme housekeeping genes (MLST) and IGS as molecular markers. The frequency of the Borrelia spp. in humans is compared to the frequency in questing ticks to assess the infectivity of the various genospecies and genotypes. The fraction of STs that were isolated from human samples was significantly higher for the genospecies that are known to be maintained in enzootic cycles by mammals (B. afzelii, B. bavariensis, and spielmanii) than for genospecies that are maintained by birds (B. garinii and B. valaisiana) or lizards (B. lusitaniae). Just as in questing ticks, B. afzelii was the most prevalent Borrelia in in human Lyme borreliosis. Borrelia afzelii was associated with acrodermatitis chronica atrophicans, while B. garinii and B. bavariensis were associated with neuroborreliosis. Despite its high incidence in ticks and erythema migrans, in terms of disease burden (as measured by disability-adjusted life year), B. afzelii is of least concern for public health. Other Borrelia spirochaetes that are rarely found in questing I. ricinus ticks, such as B. bavariensis, seem to be responsible for most of the neuroborreliosis cases – a more severe clinical symptom of Lyme borreliosis. This implies that the prevalence of B. burgdorferi s.l. in questing ticks does not necessarily reflect the incidence of human Lyme borreliosis. We found six multilocus sequence types that were significantly associated with clinical manifestations in humans and five IGS haplotypes that were associated with the human Lyme borreliosis cases. While IGS could perform just as well as the housekeeping genes in the MLST scheme for predicting the infectivity of B. burgdorferi s.l., the advantage of MLST is that it can also capture the differential invasiveness of the various STs.

    In this thesis, I have identified the most important vertebrate hosts for maintenance of B. burgdorferi s.l. in enzootic cycles. I have also shown that their density is reflected in the prevalence of B. burgdorferi s.l. in questing ticks. The comparative study of questing ticks and Lyme borreliosis indicated that some of the Borrelia genospecies have similar prevalences in the two sources. The findings in my thesis indicate, thus, that there is a link between the density of suitable hosts for ticks and Borrelia spp., the density of infected ticks and the distribution of the B. burgdorferi s.l. genospecies in Lyme borreliosis. There are exceptions, however, that cannot be explained by this simple thread line. Such a situation is the perceived association of B. bavariensis with rodents that is not reflected by its extremely low prevalence in questing ticks. Furthermore, this low prevalence cannot explain the overrepresentation of B. bavariensis in Lyme borreliosis. As result of the study of pathogenicity of the various Borrelia genospecies and genotypes, I suggest the separate hazard assignment for the Borrelia genospecies; this, in combination with the exposure (prevalence in questing ticks) would allow for individual genospecies/genotypes risk assessment. The findings in this thesis stress the importance of both ecological and clinical studies for addressing the public health issue of Lyme borreliosis.

    Push-pull tactics to disrupt the host-seeking behaviour of malaria mosquitoes
    Menger, D.J. - \ 2015
    Wageningen University. Promotor(en): Willem Takken; Joop van Loon. - Wageningen : Wageningen University - ISBN 9789462576070 - 173
    culicidae - anopheles - vectoren, ziekten - malaria - gedrag bij zoeken van een gastheer - insectenlokstoffen - insectenafweermiddelen - insectenvallen - vectorbestrijding - culicidae - anopheles - disease vectors - malaria - host-seeking behaviour - insect attractants - insect repellents - insect traps - vector control

    Malaria remains a major health burden, especially in sub-Saharan Africa. The efficacy of the main vector control tools, insecticide-treated bed nets (ITNs) and indoor residual spraying (IRS), is compromised by the development of physiological and behavioural resistance in the target mosquito species and by changes in the species composition of vector populations. These developments underline the need to develop novel vector control approaches which are complementary to insecticide-based methods. In this thesis, the potential of push-pull tactics as a tool to reduce malaria transmission is explored. It is described how the push-pull concept, originally designed for agricultural pest control, may be translated in a system that targets Anopheles mosquitoes. Several novel repellents are identified in the laboratory and a prototype push-pull system is tested in a semi-field setup. The system is improved and evaluated in a malaria endemic field setting and the push-pull approach is compared and combined with the existing practise of eave screening. Based on the experimental results it is concluded that (1) it is possible to reduce house entry of malaria and other mosquitoes using (spatial) repellents and/or attractant-baited traps; (2) the effect of repellents on house entry is larger and more consistent than the effect of attractant-baited traps; (3) the main function of the attractant-baited traps is to deplete mosquito populations through removal trapping; (4) the attractive and repellent components of the push-pull system complement each other and there is no or very little interaction between them; (5) a push-pull system based on repellent and attractive volatiles can be expected to reduce malaria transmission through a strong decrease of the entomological inoculation rate; (6) eave screening is a highly efficient method to reduce house entry of malaria and other mosquitoes and increases outdoor trap catches, while there is little added value in impregnating screening material with a repellent. In the last chapter, the issue of selection for insensitivity to the used compounds is discussed, as well as methods how to manage it. Furthermore, it is described how the principles of behavioural disruption on which push-pull tactics are based make the technique potentially suitable to target a wider selection of arthropod vectors of disease than malaria mosquitoes alone. It is concluded that future vector control strategies will probably consist of the integration of many different approaches, of which push-pull tactics may be one. By integrating different approaches, it will be possible mitigate the development of resistance while targeting vectors in different life stages, uncompromised by changing behavioural patterns and changes in the composition of vector populations. This would require an integrated view on vector control, knowledge on the ecology of vectors and the political will to invest in programmes that focus on long term sustainable control.

    Overdracht en bestrijding van fytoplasma’s in hyacint : overdracht en bestrijding van het fytoplasma, dat Lissers veroorzaakt in hyacint
    Vreeburg, P.J.M. ; Korsuize, C.A. - \ 2014
    Lisse : Praktijkonderzoek Plant & Omgeving, Business Unit Bloembollen, Bomen en Fruit - 31
    bloembollen - hyacinthus - plantenziekteverwekkende bacteriën - vectoren, ziekten - macrosteles sexnotatus - besmetting - landbouwkundig onderzoek - dalbulus - ornamental bulbs - hyacinthus - plant pathogenic bacteria - disease vectors - macrosteles sexnotatus - contamination - agricultural research - dalbulus
    De laatste jaren (2007 t/m 2010) is er in de broeierij van hyacinten en hyacint-achtigen (met name Muscari) een duidelijke toename van zogenaamde ‘Lissers’ waargenomen. ‘Lissers’, een ziekte die wordt gekenmerkt door een iele plant, die niet of nauwelijks bloeit en een slechte beworteling heeft, wordt veroorzaakt door een infectie met een fytoplasma (uit de “Aster Yellows” groep), een celwandloze bacterie die door (dwerg)cicaden (met name Macrosteles sexnotatus) van plant tot plant wordt verspreid. Het is het zelfde fytoplasma dat de vergelings-heksembezemziekte bij gladiool veroorzaakt. Er wordt verwacht dat door de klimaatsveranderingen de komende jaren het aantal besmettingen met fytoplasma’s in het voorjaar zal toenemen. Gedurende 3 jaar is onderzocht of de ligging van het teeltperceel van invloed is op het voorkomen van ‘Lissers’. Ook is het moment van voorkomen van (besmette) cicaden gemonitord en is de periode waarin besmetting met het fytoplasma plaatsvindt onderzocht.
    Lissers in hyacint blijvend, maar beheersbaar probleem
    Vreeburg, P.J.M. ; Korsuize, C.A. ; Pham, K.T.K. - \ 2014
    BloembollenVisie 2014 (2014)296. - ISSN 1571-5558 - p. 20 - 21.
    hyacinthus - macrosteles sexnotatus - vectoren, ziekten - insectenplagen - cicadelloidea - besmetting - bestrijdingsmethoden - landbouwkundig onderzoek - hyacinthus - macrosteles sexnotatus - disease vectors - insect pests - cicadelloidea - contamination - control methods - agricultural research
    Lissers in hyacinten kwamen de afgelopen jaren veel vaker voor dan voorheen. Reden voor PPO om nader onderzoek uit te voeren naar dit verschijnsel. In dit artikel is te lezen waar telers rekening mee moeten houden. Heetstoken helpt, evenals voldoende lang doorspuiten met een insecticide.
    Komkommerbontvirus en overdracht via insecten
    Stijger, I. ; Hamelink, R. - \ 2013
    Bleiswijk : Wageningen UR Glastuinbouw (Rapport GTB 1275) - 18
    komkommerbontvirus - plantenziekten - waardplanten - cucumis sativus - komkommers - insectenpathogenen - gewasbescherming - vectoren, ziekten - glastuinbouw - landbouwkundig onderzoek - cucumber green mottle mosaic virus - plant diseases - host plants - cucumis sativus - cucumbers - entomopathogens - plant protection - disease vectors - greenhouse horticulture - agricultural research
    Bekend is dat komkommerbontvirus (cucumber green mottle mosaic virus, CGMMV) via mechanische overdracht en zaad kan worden verspreid. Via de vele gewashandelingen die door mensen worden uitgevoerd is overdracht van het virus mogelijk van plant naar plant. Een vraag die regelmatig wordt gesteld is of insecten in staat zijn het virus over te brengen. Vooral stekende en/of zuigende insecten kunnen in staat zijn om plantenvirussen over te brengen. Dit kan op een non-persistente manier, dit wil zeggen dat een insect het virus van een plant kan opnemen en gelijk weer afgeven op een andere plant. Is deze plant geen waardplant voor het virus dan zal het insect na het aanprikken van de plant gelijk weer ‘virusvrij’ zijn. Bij een persistente wijze wordt het virus in een insect opgenomen en kan het virus na een bepaalde periode pas weer worden afgegeven aan een andere plant. Het insect is dan gedurende langere tijd in staat om virussen van de ene naar de andere plant te brengen. Uit de literatuur met betrekking tot komkommerbontvirus is nauwelijks onderzoek bekend waarbij werkelijk is gekeken naar de overdracht door verschillende insecten. Voor zover nu bekend is een onderzoek van Inouye uit 1967 een van de weinige waarin is nagegaan wat de rol van de bladluizen Myzus persicae en Aphis gossypii is bij de overdracht van komkommerbontvirus. In dat onderzoek kon geen overdacht worden vastgesteld. Trips is een veelvoorkomend insect in de komkommerteelt en is ook bekend als vector van virussen die tot de Tospo-groep behoren. Een voorbeeld hiervan is tomatenbronsvlekkenvirus, maar komkommer is geen waardplant voor dit virus. Of trips komkommerbontvirus zou kunnen overbrengen is niet bekend. Net als bladluizen en trips is ook (kas) witte vlieg bekend als een vector van plantenvirussen. Deze insecten zijn dan ook in het onderzoek worden meegenomen. In een eerder uitgevoerd onderzoek bij tomaten is vastgesteld dat hommels in staat zijn om het pepinomozaïekvirus te verspreiden van plant naar plant. Echter hommels worden niet ingezet in de komkommer teelt en zijn daarom niet meegenomen in dit onderzoek.
    Inventarisatie, voorkoming en bestrijding van fytoplasma en zijn vector in Muscari. Voortgezet diagnostisch onderzoek 2010/2011
    Vink, P. ; Leeuwen, P.J. van; Pham, K.T.K. - \ 2013
    Lisse : Praktijkonderzoek Plant & Omgeving BBF - 13
    bloembollen - muscari - phytoplasma - bacteriën - cicadellidae - vectoren, ziekten - vectorbestrijding - heetwaterbehandeling - imidacloprid - ornamental bulbs - muscari - phytoplasma - bacteria - cicadellidae - disease vectors - vector control - hot water treatment - imidacloprid
    Bij de broei van Muscari op pot kwamen vanaf 2007 veel klachten voor van ongelijke beworteling en ongelijke gewasontwikkeling uit ogenschijnlijk volkomen gezonde Muscaribollen. Aanvankelijk werd gedacht aan schade door herbiciden of het moment van rooien van de Muscaribollen voorafgaande aan het broeiseizoen. Uit (voortgezet) diagnostisch onderzoek bleek dat daarvan geen sprake was. In 2010 bleek uit diagnostisch onderzoek dat in Muscaribollen met achterblijvende beworteling en groei in de broeierij regelmatig fytoplasma kon worden aangetoond. In 2010 is ook fytoplasma in Scilla mischtschenkoana aangetoond met vergelijkbare symptomen als bij Muscari en hyacinten. Daarmee werd duidelijk dat bij Muscari, en incidenteel ook Scilla, sprake kan zijn van zogenaamde “Lissers” zoals we dit ook kennen bij hyacinten.Om meer inzicht te krijgen in deze voor Muscari nieuwe ziekte en om na te gaan of fytoplasma’s in Muscaribollen zijn te bestrijden is voortgezet diagnostisch onderzoek uitgevoerd. Daarbij zijn via verschillende kanalen extra monsters Muscari’s uit de broeierij verzameld en middels PCR-technieken getoetst op fytoplasma’s. Het bleek dat in veel partijen Muscaribollen die op zogenaamde “luwe tuinen” waren geteeld in de broeierij regelmatig sprake was van achterblijvende planten waarin fytoplasma kon worden aangetoond. Het betrof steeds het fytoplasma dat tot de Aster Yellows Group (16Sr-I) behoorde. Dit is dezelfde groep fytoplasma die bij hyacint “Lissers” kan veroorzaken. Het werd duidelijk dat het probleem van een fytoplasma-besmetting in partijen Muscaribollen groter was dan men aanvankelijk dacht. Dit maakt het dan ook noodzakelijk dat tijdens de bollenteelt van Muscari extra aandacht wordt geschonken aan de bestrijding van dwergcicaden, de vector van fytoplasma. Daarom is in 2010 een vakbladartikel gepubliceerd in BloembollenVisie om de bollentelers van Muscaribollen te informeren over de nieuwe ziekte waardoor ze in het lopende groeiseizoen nog in staat waren om maatregelen te nemen tegen (dwerg)cicaden.In 2010 en 2011zijn ook slecht bewortelde Muscaribollen uit de broeierij verzameld om na te gaan of met behulp van een warmwaterbehandeling fytoplasma is te doden. Ook is nagegaan of een boldompeling vóór het planten in imidacloprid (Admire) effectief beschermend kan werken tegen dwergcicaden waardoor de overdracht en verspreiding van fytoplasma’s in Muscari tijdens de bollenteelt kan worden voorkomen. Het bleek dat een warmwaterbehandeling van 2 uur bij 43,5ºC geen meetbare dodingseffect had op fytoplasma. Van deze cultuurkook mag in de praktijk dus niets worden verwacht ten aanzien van de doding van fytoplasma in Muscaribollen. Ook een warmwaterbehandeling van 4 uur 45ºC gaf geen volledige doding van fytoplasma in Muscari. Of imidacloprid (Admire) een effect heeft gehad op het besmet raken van Muscaribollen door fytoplasma is onduidelijk gebleven. Tijdens de veldproef was het niet mogelijk voldoende ziektedruk aan te leggen voor overdrachtsexperimenten De conclusie is dan ook dat een warmwaterbehandeling van leverbare Muscaribollen geen voldoende oplossing biedt om een besmetting met fytoplasma te bestrijden. Vooralsnog is dus de beste methode om een besmetting met fytoplasma te voorkomen door middel van perceelkeuze het gewas tijdens de bollenteelt vrij te houden van dwergcicaden zodat deze de fytoplasma niet kunnen overdragen op het Muscarigewas.
    Identification of Arabidopsis thaliana genes that can increase resistance towards phloem feeding insects
    Chen, X. - \ 2013
    Wageningen University. Promotor(en): Richard Visser, co-promotor(en): Ben Vosman. - [S.l.] : S.n. - ISBN 9789461737649 - 96
    arabidopsis thaliana - insectenplagen - myzus persicae - plaagresistentie - genkartering - genexpressie - mutanten - plantenveredeling - turnip yellows virus - vectoren, ziekten - arabidopsis thaliana - insect pests - myzus persicae - pest resistance - gene mapping - gene expression - mutants - plant breeding - turnip yellows virus - disease vectors

    Phloem feeding insects are among the most devastating pests worldwide. They not only cause damage by feeding from the phloem, but also by vectoring plant viruses. During their evolution plants have developed a variety of defense traits to combat insects. These plant resistance traits can be antixenotic and/or antibiotic. Antixenosis is the first line of defense that prevents insects from landing and settling, while antibiosis reduces the population development of the colonizing insects.In this project we aimed at identifying genes that can increase resistance towards phloem feeding insects and also prevent, as far as possible, transmission of viruses. Acknowledging that changing the expression level or expression localization of genes might increase resistance, we screened an Arabidopsis thaliana activation tag gain-of-function mutant collection for increased resistance towards the green peach aphid (Myzus persicae). In these mutants, tagged genes are overexpressed by the strong 35S enhancer adjacent to the natural promoter that results in a dominant gain-of-function phenotype. The overexpression of a particular gene in such mutants may result in enhanced resistance to aphids and other phloem feeding insects.

    To identify mutants with increased insect resistance efficient and reproducible screening methods needed to be developed first. Based on the hypothesis that there is a trade-off between plant fitness and plant resistance, we first screened a subset of 170 mutants that were previously selected based on their reduced growth to increase the chance of identifying mutants with increasedresistance. In this screening we usedchoice assays and selected one mutant that displays enhanced antixenosis based resistance towards aphids. Further characterization of this mutant revealed that that the antixenosis is phloem based and requires intact plants.

    To evaluate aphid resistance of a larger number (>5000) of activation tag mutants, we established a high throughput screening system in which plant resistance against aphids is inferred from a reduced transmission of the circulative Turnip yellows virus(TuYV). This virus can only be transmitted into a plant after virus-infected aphids feed for a prolonged (> 10min) time from the phloem sap. In the initial screening 13 virus-free mutant lines were identified. The putative candidate mutant lines were re-evaluated and characterized, resulting in nine mutants on which aphids showed a reduced population development.

    Molecular analysis of two of these mutants revealed that the genes underlying the resistance were IRM1(Increased ResistancetoMyzus persicae1,At5g65040)and SKS13 (SKU5Similar13, At3g13400). In wild type plants,IRM1is strongly expressed in xylem and extremely low expressed in other plant tissue whereas SKS13 is exclusively expressed in pollen. We show that constitutive overexpression of these genes in all plant tissues confers enhanced resistance towards aphids. Analysis of aphid feeding behavior showed that the resistance conferred by IRM1and SKS13affect the aphids differently. On the IRM1 overexpressing mutant aphids encounter difficulties in reaching the phloem, indicating that resistance factors are located between the cell surface and the phloem. On the SKS13overexpressingmutant the phloem feeding of aphids is severely affected, indicating that resistance factors are phloem based. Further analysis strongly suggests the involvement of Reactive Oxygen Species (ROS) in the reduced aphid performance on the SKS13overexpressingmutant. We also show that the resistances are not aphid specific, as the performance of the cabbage aphid (Brevicoryne brassicae)is also affectedon both overexpressing mutants.

    The results obtained in this thesis show that plant resistance to insects can be increased by expressing genes that are assigned for other biological functions. Characterization of the identified mutants revealed twogenes conferring enhanced aphid resistance via different mechanisms. These findings lead to a better understanding of plant-aphid interactions on the molecular level. Furthermore, such knowledge obtained from the model plant A.thalianashould be applied in crop plants, which can be achieved by transgenic and genetic studies in combination with newly developed techniques, such as RNAi and TILLING.

    Resistance to thrips in pepper
    Maharijaya, A. - \ 2013
    Wageningen University. Promotor(en): Richard Visser, co-promotor(en): Roeland Voorrips; Ben Vosman. - Wageningen : Wageningen UR - ISBN 9789461737397 - 110
    capsicum - capsicum annuum - capsicum chinense - paprika's - spaanse pepers - insectenplagen - vectoren, ziekten - frankliniella occidentalis - thrips - plaagresistentie - loci voor kwantitatief kenmerk - soortkruising - plantenveredeling - capsicum - capsicum annuum - capsicum chinense - sweet peppers - chillies - insect pests - disease vectors - frankliniella occidentalis - thrips - pest resistance - quantitative trait loci - interspecific hybridization - plant breeding

    Pepper (Capsicum) production is constrained by heavy infestations of thrips, causing direct and indirect (by transmitting viruses) damage. Thrips control using chemical insecticides, biological agents, culture practices and integrated pest management has limited success. The availability of thrips-resistant varieties would increase the effectiveness of thrips control and may also delay and reduce the transmission of viruses. This thesis is aimed at obtaining more knowledge regarding thrips resistance in pepper, including the identification of new sources of resistance, the elucidation of resistance mechanisms, identification of factors contributing to resistance and a QTL analysis.

    We developed several test methods to evaluate plant resistance to thrips and showed that in vitro tests correlate well with greenhouse tests. We used these methods to test a collection of Capsicum accessions of widely different origin and crop types. This resulted in the identification of a few accessions (mostly C. annuum) with high levels of resistance to two thrips species: Frankliniella occidentalis and Thrips parvispinus. Since C. annuum is the most widely cultivated species, the finding of resistance in C. annuum is means that the resistance can be easily introgressed through conventional crossing and selection.

    The effect of resistance in pepper on thrips reproduction and development was studied using three highly resistant, three medium resistant and three susceptible accessions selected based on damage ratings. Adult and pre-adult survival, developmental time and reproduction rate were assessed in a detached leaf system. Resistance factors in leaves of resistant pepper accessions were shown to have significant effects on oviposition rate, larval mortality and life-cycle period, indicating that this resistance is based on antibiosis.

    In order to map QTL for resistance we developed an F2 population from the cross between a susceptible C. chinense accession and the resistant C. annuum AC 1979. A genetic linkage map for this population was based on AFLP and SSR markers, where the SSR markers served to assign and orient most linkage groups to pepper chromosomes. As larval stages were highly affected by resistance in pepper leaves, damage caused by larvae and larval survival were used as parameters to detect QTLs conferring resistance to thrips. Interval mapping detected one QTL for each of these parameters, all co-localizing near the same marker on chromosome 6. This QTL explained about 50% of the genetic variation, and the resistance allele of this QTL was inherited from the resistant parent. No other resistance QTLs were detected in this population.

    Since resistance to thrips was clearly expressed in pepper leaves we proceeded to study leaf traits that may contribute to resistance. Morphological leaf characters and metabolites have frequently been linked with resistance to thrips in other plant species. However, we found no convincing evidence that any of these traits played a role in thrips resistance in pepper. In the F2 mapping population we found no correlation and no QTL co-localization of resistance with leaf morphological characters previously linked to resistance in pepper against insect pest and in other plant species against thrips e.g. color, toughness, trichome density, and cuticula thickness. GC-MS (Gass Chromatography – Mass Spectrometry) analysis of the three resistant, three intermediate and three susceptible accessions mentioned above showed that seven metabolites were correlated with resistance to thrips and six compounds with susceptibility. However, when we applied GC-MS and LC-MS (Liquid Chromatography – Mass Spectrometry) to leaves of the F2 mapping population, we found no strong correlation between resistance and any detected metabolites. Two metabolite QTLs co-localized with the resistance QTL. However, these QTLs explained only a small proportion of the variance and the co-localization was not supported by strong correlations of the metabolites with resistance. This suggests that the major resistance factor(s) in pepper against thrips may not or only partially be determined by the presence or absence of specific metabolites.

    This thesis provides a strong basis for the development of thrips resistant pepper varieties through introgression of the resistance QTL region on chromosome 6 originating from resistant C. annuum accessions. However, the effect of resistance QTL on chromosome 6 should be confirmed in another population such as a population of F3 lines. In vitro leaf assay can be used as evaluation methods in pepper breeding program. This has the advantages of minimizing the risk of contamination and of controlled environmental conditions. Elucidation of factors contributing to resistance should be continued by giving attention to other possibilities such as proteins, specifically proteinase inhibitors, or other leaf anatomical and morphological traits. Also other extraction and detection methods may be used to discover other metabolites that might be related to resistance. Finally, for practical applications it is necessary study how to use the antibiosis based mechanism against thrips found in this thesis in thrips control and/or management practices.

    Culicoides obsoletus allergens for diagnosis of insect bite hypersensitivity in horses
    Meide, N.M.A. van der - \ 2013
    Wageningen University. Promotor(en): Huub Savelkoul, co-promotor(en): Edwin Tijhaar. - S.l. : s.n. - ISBN 9789461736697 - 228
    paarden - equus - culicoides obsoletus - insectenbeten - allergenen - overgevoeligheid - allergieën - cytokinen - diagnose - elisa - vectoren, ziekten - immunologie - horses - equus - culicoides obsoletus - insect bites - allergens - hypersensitivity - allergies - cytokines - diagnosis - elisa - disease vectors - immunology

    AInsect Bite Hypersensitivity (IBH) is the most common skin allergy in horses and involves a Type I (IgE mediated) hypersensitivity reaction against bites of insects, mainly of the Culicoides species. Welfare of affected horses is seriously reduced and no fully curative treatment is yet available. Furthermore, current diagnostic tests are unreliable because of their low sensitivity and specificity. Aim of our research was to increase the understanding of immunological aspects of IBH, with special attention to improving diagnosis by the characterization and production of recombinant allergens.

    Whole body extracts (WBE) of three Culicoides species: C. obsoletus C. nubeculosus and C. sonorensis were evaluated for their applicability for diagnosis of IBH in horses in The Netherlands. They were tested for IgE binding by ELISA and Western blotting and for their capacity to degranulate basophils in a histamine release test. For all tests, best results were obtained with C. obsoletus. The ELISA was further evaluated using C. obsoletus extract on approximately 200 IBH affected and healthy horses, which demonstrated high test sensitivity and specificity. C. obsoletus-specific IgE serum levels were found to be the same in the IBH season and off season, suggesting that the test can be used to diagnose horses in winter when clincial symptoms are absent.

    Since C. obsoletus was found to be the most important species for diagnosis of IBH in The Netherlands, mRNA of this Culicoides species was sequenced and assembled to create a transcriptome. Using the sequences from in literature described allergens from C. nubeculosus and C. sonorensis, similarity searches were performed on this transcriptome,. This resulted in the identification of seven allergens from C. obsoletus. These allergens were cloned and expressed as recombinant proteins in E. coli and named Cul o 1 – Cul o 7. The frequency of positive test results by ELISA within IBH affected horses ranged from 38 % to 67 %. The capability of the allergens to induce Type I hypersensitivity reaction in IBH affected horses was demonstrated by an intradermal test.

    The applicability of the 7 C. obsoletus derived recombinant allergens was further evaluated and compared with C. obsoletus WBE in an IgE ELISA using a large number of horses.The highest test accuracy was obtained with WBE, followed by Cul o 2, 3 and 5. Two ELISA’s with a combination of recombinant allergens, combi-1 (Cul o 3, 5 and 7) and combi-2 (Cul o 1, 2, 5 and 7) were additionally performed and both resulted in high test accuracies close to that obtained with WBE. Both combi-1 and combi-2 resulted in a lower test sensitivity with samples collected in winter compared to samples collected in IBH season, but most IBH affected horses could still also be correctly diagnosed in winter.

    The association between several factors and IgE levels against C. obsoletus whole body extract and the 7 recombinant allergens was quantified. Furthermore, the relation between IgE levels and severity of symptoms was examined. Severity of symptoms and IgE levels against several C. obsoletus allergens were found to be related. Factors that were found to be associated with IgE levels were: breed, age, month of scoring, interaction between IBH status and month of scoring, degree of itchiness and number of seasons horses were affected with IBH.

    The general discussion discussed the prospects to use the produced recombinant allergens for immunotherapy treatment of IBH affected horses. The panel of all 7 recombinant allergens allows to determine for which exact components of C. obsoletus the IBH horses are allergic (“component resolved diagnosis”). This will enable a tailor made composition of (recombinant) allergens for use in immunotherapy.

    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.

    Ecology of parasite-vector interactions
    Takken, W. ; Koenraadt, C.J.M. - \ 2013
    Wageningen : Wageningen Academic Publishers (Ecology and control of vector-borne diseases vol. 3) - ISBN 9789086861880 - 272
    gastheer parasiet relaties - parasieten - vectoren, ziekten - ziekten overgebracht door vectoren - vectorbestrijding - ecologie - medische entomologie - host parasite relationships - parasites - disease vectors - vector-borne diseases - vector control - ecology - medical entomology
    Vector-borne diseases continue to be one of the most important determinants affecting human and animal health. Large numbers of people suffer from diseases like malaria, dengue, filariasis and leishmaniasis, especially in the tropics. Whereas these diseases were eradicated from the temperate climate zones, in recent years the rising incidence of 'emerging' vector-borne diseases such as bluetongue, West Nile Virus, Lyme disease, tick-borne encephalitis and the recent outbreaks of chikungunya and dengue in southern Europe provide evidence that these diseases are resilient and can disperse to other regions and continents where before they were not present or relevant. Many tools for the management of vector-borne diseases are currently under pressure because of increasing drug and insecticide resistance, as well as the realization of biological variation of parasites and vectors and their ecosystems. At the same time, progress in our understanding of genetics, immunology, population biology and epidemiology allow for a better understanding of parasite-vector interactions. Here the state-of-the-art of these interactions is being reviewed, and means for using this information for advanced strategies of vector-borne disease control are proposed. This 3rd edition of ECVD aims to provide a rapid overview of recent developments in the field of parasite-vector interactions and how this can be used for more effective and sustainable disease control.
    Behavioural effects of fungal infection by Metarhizium anisopliae in adult malaria mosquitoes
    Ondiaka, S.N. - \ 2012
    Wageningen University. Promotor(en): Willem Takken; Marcel Dicke, co-promotor(en): W.R. Mukabana. - S.l. : s.n. - ISBN 9789461732934 - 179
    anopheles gambiae - vectoren, ziekten - malaria - vectorbestrijding - biologische bestrijding - metarhizium anisopliae - diergedrag - paringsgedrag - gedrag bij zoeken van een gastheer - voedingsgedrag - ovipositie - anopheles gambiae - disease vectors - malaria - vector control - biological control - metarhizium anisopliae - animal behaviour - mating behaviour - host-seeking behaviour - feeding behaviour - oviposition

    Malaria remains a major global health problem with the burden of disease greatest in Sub-Saharan Africa. The strategies for malaria control differ throughout the world according to levels of endemicity and the magnitude of disease but the focus remains either to control malaria parasites or vectors. A high degree of drug resistance and the absence of malaria vaccines are a major hindrance to control of the disease. In such circumstances, vector control becomes an alternative and has remained the most effective means to prevent malaria transmission. Contemporary adult mosquito control is almost exclusively based on indoor application of chemical insecticides in the form of indoor residual spraying (IRS) of walls and ceilings and insecticide-impregnated bed nets. However, sustainable use of chemicals is undermined by problems of insecticide resistance in mosquito populations, environmental contamination and risks to human health. Biological control based on fungal pathogens has shown potential to complement existing vector control methods. The entomopathogenic fungi (EPF) Metarhizium anisopliae and Beauveria bassiana have demonstrated ability to infect, kill and reduce the survival of malaria vectors. However, the effect of EPF on the behaviour of malaria vectors has not been fully addressed.

    This thesis was designed to provide baseline information on mosquito-fungus interaction focusing on the efficacy of entomopathogenic fungus M. anisopliae ICIPE 30 on the important life-history behaviours of the African malaria vector Anopheles gambiae Giles sensu stricto under laboratory and semi-field conditions. The information is important to facilitate the further development of malaria vector control based on biological control agents. Host-seeking, sugar-feeding, mating and oviposition were the behaviours investigated. Since mosquito-fungus contact is crucial for infection with EPF, a paper sheet (28.6 × 14.3 cm) lined inside a plastic cylinder (9-cm diameter and 15-cm height) was developed as a cost effective method of infection. Moreover, 0.1 g (approx. 1011 conidia/m2) of dry conidia and 6 hr exposure time sufficient for An. gambiae to pick up large numbers of conidia were established to cause high pathogenicity (Chapter 3). As the impact of EPF on insect behaviour was reported to occur at least three days post-exposure to fungal pathogen (Chapter 2), all experiments were conducted with a special focus on mosquitoes three days post-exposure to fungus. It is, however, important to mention that on average 50% of the mosquitoes died on the third day after fungal exposure (Chapter 3) and only those that survived were used for behavioural assays.

    The host-seeking capability of An. gambiae mosquitoes is an important parameter in the vectorial capacity equation. At short-range (1 m from host) assessment using a dual-choice olfactometer under semi-field conditions, infection with EPF strongly reduced the host-seeking response of mosquitoes, but did not impair their olfactory-based capability to discriminate between hosts (Chapter 4). At medium-range, using experimental cages (3 x 3 x 2 m) under laboratory conditions, fungal infection reduced the host-seeking response and feeding propensity of female An. gambiae mosquitoes (Chapter 7) whereas at long-range (7 m from host) inside a semi-field enclosure, infection with EPF sharply reduced the house-entry response and the hourly human-biting responses of host-seeking mosquitoes indoors and outdoors (Chapter 5). Plant sugar feeding is an important component in the biology of mosquitoes and is the main priority for both sexes at emergence. Infection with fungal pathogen strongly reduced the survival and sugar-feeding propensity of both sexes of the malaria vector An. gambiae but did not affect their potential to feed and digest meals (Chapter 6). Mating behaviour plays a key role in population growth. The activity takes place after sugar feeding and thereafter, the females search for their blood meal host. Infection with M. anisopliae strongly reduced multiple mating propensity and the mating performance of adult male An. gambiae mosquitoes in a large arena such as a screenhouse. Although this resulted in a reduction in the number of females inseminated, it facilitated the transfer of fungal conidia to conspecific healthy females during mating (Chapter 8). Finally, after blood meal intake, the females prepare to lay eggs. Infection with M. anisopliae reduced the oviposition propensity of female An. gambiae mosquitoes although the number of eggs laid remained unaffected (Chapter 7).

    In conclusion, these findings demonstrate that the entomopathogenic fungus M. anisopliae alters the major life history behaviours of An. gambiae mosquitoes. This is possible because the fungus strongly impairs flight performance of mosquitoes that makes the insect less able to fly and engage in host-seeking, sugar-feeding, mating and oviposition behaviours. The high mortalities observed in the early days of infection prior to conducting behavioural assays, mortalities observed while conducting behavioural assays and a reduction in behavioural response of M. anisopliae-infected mosquitoes collectively are likely to have a significant impact in suppressing a vector population. The susceptibility of male mosquitoes to fungal conidia opens a new strategy for mosquito vector control. Overall, this thesis has demonstrated that EPF may be a good complement to other mosquito vector control tools for the reduction of mosquito bites, and transmission of malaria and other mosquito-borne diseases.

    Meer bekend over het optreden van Lissers bij hyacint
    Vreeburg, P.J.M. ; Korsuize, C.A. ; Lemmers, M.E.C. ; Pham, K.T.K. - \ 2012
    BloembollenVisie 2012 (2012)245. - ISSN 1571-5558 - p. 24 - 25.
    hyacinthus - insectenplagen - macrosteles sexnotatus - vectoren, ziekten - plantenziekteverwekkende bacteriën - gewasbescherming - bestrijdingsmethoden - forceren van planten - hyacinthus - insect pests - macrosteles sexnotatus - disease vectors - plant pathogenic bacteria - plant protection - control methods - forcing
    Lissers is al een oud probleem dat vroeger zo nu en dan optrad, maar de laatste jaren een blijvend probleem is op sommige percelen. Voldoende kennis over de infectiebron, moment van overdracht en bestrijding ontbreekt nog. Na één jaar onderzoek is meer bekend geworden hoe het zit met de verspreiding en (on)mogelijkheden voor bestrijding. Helemaal voorkomen lijkt niet mogelijk, maar gestreefd kan worden om de bestrijding te velde zo optimaal mogelijk uit te voeren. Cicadenbestrijding lijkt voor mei niet nodig.
    Ziek en Zeer : Monitoring dwergcicaden in hyacintenveld
    Vink, P. - \ 2012
    BloembollenVisie 2012 (2012)245. - ISSN 1571-5558 - p. 23 - 23.
    hyacinthus - bloembollen - cicadelloidea - vectoren, ziekten - macrosteles sexnotatus - detectie - landbouwkundig onderzoek - hyacinthus - ornamental bulbs - cicadelloidea - disease vectors - macrosteles sexnotatus - detection - agricultural research
    Vanaf 2007 zien we jaarlijks problemen in de broeierij met zogenoemde 'Lissers' in hyacinten, veroorzaakt door een besmetting met fytoplasma's. Deze ziekteverwekker wordt tijdens de bollenteelt overgebracht door (dwerg)cicaden. Van belang leek het om na te gaan hoe vroeg in het seizoen deze insecten in Nederland actief rondvliegen en dus mogelijk ook in staat zijn om fytoplasma's te verspreiden. Het bleek dat dwergcicaden al in april waren te vangen. Dit is aanzienlijk vroeger dan werd gedacht en dus is het van belang om de juiste keuzes te kunnen maken bij bestrijding van deze insecten.
    Risk assessment framework for emerging vector-borne livestock diseases
    Vos, C.J. de; Hoek, M.R. ; Fischer, E.A.J. ; Koeijer, A.A. de; Bremmer, J. - \ 2012
    Lelystad : Wageningen UR, Central Veterinary Institute - 76
    veehouderij - dierziekten - infectieziekten - risicoschatting - risicoanalyse - besluitvorming - vectoren, ziekten - livestock farming - animal diseases - infectious diseases - risk assessment - risk analysis - decision making - disease vectors
    The objective of this project was to develop a framework for risk assessment of introduction, establishment, spread and persistence of vector-borne livestock diseases by integrating the essential elements of different approaches. This framework will help risk analysts to assess the risk of vector-borne diseases, considering both likelihood of occurrence and potential impact to inform stakeholders on behalf of their decision making.
    Hoe een modelleur een mug vangt - het nut van wiskundige modellen voor het bestuderen en bestrijden van vector-overgedragen ziekten
    Braks, M.A.H. ; Fischer, E.A.J. ; Hartemink, N. - \ 2011
    Entomologische Berichten 71 (2011)5. - ISSN 0013-8827 - p. 136 - 142.
    culicidae - epidemiologie - vectoren, ziekten - epidemiology - disease vectors
    Vector-overgedragen ziekten zijn infectieziekten die worden overgedragen door vectoren, meestal anthropoden, zoals muggen, knutten en teken. De laatste jaren is de aandacht voor deze ziekten toegenomen. Aanleidingen hiervoor zijn bijvoorbeeld de uitbraak van het West-Nijlvirus in Noord-Amerika, de recente blauwtong-epidemie in Nederland en omringende landen en de uitbraak van chikungunya in Italië.
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