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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Effect of challenge dose of plasmid-mediated extended-spectrum β-lactamase and AmpC β-lactamase producing Escherichia coli on time-until-colonization and level of excretion in young broilers
Dame-Korevaar, Anita ; Fischer, Egil A.J. ; Goot, Jeanet van der; Velkers, Francisca ; Broek, Jan van den; Veldman, Kees ; Ceccarelli, Daniela ; Mevius, Dik ; Stegeman, Arjan - \ 2019
Veterinary Microbiology 239 (2019). - ISSN 0378-1135
Animal model - Antibiotic resistance - Dose-response - Inoculation - Poultry - Transmission

Plasmid-mediated extended-spectrum β-lactamase and AmpC β-lactamase (ESBL/pAmpC) producing bacteria are present at all levels of the broiler production pyramid. Young birds can be found positive for ESBL/pAmpC-producing Escherichia coli shortly after arrival at farm. The aim of this study was to determine the effect of different challenge doses of ESBL/pAmpC-producing E. coli on time-until-colonization and the level of excretion in young broilers. One-day-old broilers (specific-pathogen free (SPF) and conventional Ross 308) were housed in isolators and challenged with 0.5 ml ESBL/pAmpC-producing E. coli strains of varying doses (101–105 CFU/ml). Presence and concentration (CFU/gram feces) of ESBL/pAmpC-producing E. coli and total E. coli were determined longitudinally from cloacal swabs, and in cecal content 72 h after challenge. Higher challenge doses resulted in shorter time-until-colonization. However, even the lowest dose (101 CFU/ml) resulted in colonization of the broilers which excreted >106 CFU/gram feces 72 h after inoculation. Conventional broilers were colonized later than SPF broilers, although within 72 h after challenge all broilers were excreting ESBL/pAmpC-producing E. coli. A probabilistic model was used to estimate the probability of colonization by initial inoculation or transmission. The higher the dose the higher the probability of excreting ESBL/pAmpC-producing E. coli as a result of inoculation. In conclusion, low initial doses of ESBL/pAmpC-producing E. coli can result in rapid colonization of a flock. Interventions should thus be aimed to eliminate ESBL/pAmpC-producing bacteria in the environment of the hatchlings and measures focusing at reducing colonization and transmission of ESBL/pAmpC-producing E. coli should be applied shortly after hatching.

Subgenomic flavivirus RNA binds the mosquito DEAD/H-box helicase ME31B and determines Zika virus transmission by Aedes aegypti
Göertz, Giel P. ; Bree, Joyce W.M. van; Hiralal, Anwar ; Fernhout, Bas M. ; Steffens, Carmen ; Boeren, Sjef ; Visser, Tessa M. ; Vogels, Chantal B.F. ; Abbo, Sandra R. ; Fros, Jelke J. ; Koenraadt, Constantianus J.M. ; Oers, Monique M. van; Pijlman, Gorben P. - \ 2019
Proceedings of the National Academy of Sciences of the United States of America 116 (2019)38. - ISSN 0027-8424 - p. 19136 - 19144.
Aedes aegypti - Purification - RNA-affinity - Subgenomic flavivirus RNA - Transmission - Zika virus

Zika virus (ZIKV) is an arthropod-borne flavivirus predominantly transmitted by Aedes aegypti mosquitoes and poses a global human health threat. All flaviviruses, including those that exclusively replicate in mosquitoes, produce a highly abundant, noncoding subgenomic flavivirus RNA (sfRNA) in infected cells, which implies an important function of sfRNA during mosquito infection. Currently, the role of sfRNA in flavivirus transmission by mosquitoes is not well understood. Here, we demonstrate that an sfRNA-deficient ZIKV (ZIKVΔSF1) replicates similar to wild-type ZIKV in mosquito cell culture but is severely attenuated in transmission by Ae. aegypti after an infectious blood meal, with 5% saliva-positive mosquitoes for ZIKVΔSF1 vs. 31% for ZIKV. Furthermore, viral titers in the mosquito saliva were lower for ZIKVΔSF1 as compared to ZIKV. Comparison of mosquito infection via infectious blood meals and intrathoracic injections showed that sfRNA is important for ZIKV to overcome the mosquito midgut barrier and to promote virus accumulation in the saliva. Next-generation sequencing of infected mosquitoes showed that viral small-interfering RNAs were elevated upon ZIKVΔSF1 as compared to ZIKV infection. RNA-affinity purification followed by mass spectrometry analysis uncovered that sfRNA specifically interacts with a specific set of Ae. aegypti proteins that are normally associated with RNA turnover and protein translation. The DEAD/H-box helicase ME31B showed the highest affinity for sfRNA and displayed antiviral activity against ZIKV in Ae. aegypti cells. Based on these results, we present a mechanistic model in which sfRNA sequesters ME31B to promote flavivirus replication and virion production to facilitate transmission by mosquitoes.

Transmission of African Swine Fever Virus via carrier (survivor) pigs does occur
Eblé, P.L. ; Hagenaars, T.J. ; Weesendorp, E. ; Quak, S. ; Moonen-Leusen, H.W. ; Loeffen, W.L.A. - \ 2019
Veterinary Microbiology 237 (2019). - ISSN 0378-1135
African Swine Fever - Carrier - Environment - Reproduction ratio - Survivor - Transmission

We investigated whether ASF carrier pigs that had completely recovered from an acute infection with ASFV Netherlands ‘86, could transmit the disease to naive pigs by direct contact transmission. For this, we used pigs that had survived an ASFV infection, had recovered from disease, and had become carriers of ASFV. These clinically healthy carriers were put together one-by-one with naive contact pigs. Two of the twelve contact pigs developed an acute ASFV infection. Using the results of the experiment we quantified the transmission parameters βcarrier (0.039/day) and Tcarrier (25.4 days). With the survival rate of 0.3 for our ASFV isolate, these parameter values translate into the contribution of carriers to R0 in groups of pigs being 0.3. Further, we placed naive contact pigs in an ASFV contaminated environment. Here, no contact infections were observed. Our findings show that clinically healthy carriers can be a source of acute new infections, which can contribute to the persistence of ASFV in swine populations. The estimates that we provide can be used for modelling of transmission in domestic pigs and, in part, for modelling transmission in wild boar.

Exploring contacts facilitating transmission of influenza A(H5N1) virus between poultry farms in West Java, Indonesia : A major role for backyard farms?
Wibawa, Hendra ; Karo-Karo, Desniwaty ; Pribadi, Eko Sugeng ; Bouma, Annemarie ; Bodewes, Rogier ; Vernooij, Hans ; Diyantoro, ; Sugama, Agus ; Muljono, David H. ; Koch, Guus ; Tjatur Rasa, Fadjar Sumping ; Stegeman, Arjan - \ 2018
Preventive Veterinary Medicine 156 (2018). - ISSN 0167-5877 - p. 8 - 15.
Avian influenza - Contact structure - H5N1 - Indonesia - Poultry - Transmission
Highly pathogenic avian influenza virus (HPAIV) H5N1 has been reported in Asia, including Indonesia since 2003. Although several risk factors related to the HPAIV outbreaks in poultry in Indonesia have been identified, little is known of the contact structure of farms of different poultry production types (backyard chickens, broilers, layers, and ducks). This study aims to quantify the contact rates associated with the movement of people, and movements of live birds and products and equipment that affect the risk of HPAIV H5N1 transmission between poultry farms in Indonesia. On 124 poultry farms in 6 districts in West Java, logbooks were distributed to record the movements of farmers/staff and visitors and their poultry contacts. Most movements in backyard chicken, commercial native chicken, broiler and duck farms were visits to and from other poultry farms, whilst in layer farms visits to and from poultry companies, visits to egg collection houses and visit from other poultry farms were most frequent. Over 75% of persons visiting backyard chicken and duck farms had previously visited other poultry farms on the same day. Visitors of backyard chicken farms had the highest average contact rate, either direct contact with poultry on other farms before the visits (1.35 contact/day) or contact during their visits in the farms (10.03 contact/day). These results suggest that backyard chicken farms are most at risk for transmission of HPAIV compared to farms of the other poultry production types. Since visits of farm-to-farm were high, backyard farms could also a potential source for HPAIV transmission to commercial poultry farms.
Farming, Q fever and public health : Agricultural practices and beyond
Mori, Marcella ; Roest, Hendrik Jan - \ 2018
Archives of Public Health 76 (2018)1. - ISSN 0778-7367
Agricultural practices - Control - Coxiella burnetii - One health - Surveillance - Transmission
Since the Neolithic period, humans have domesticated herbivores to have food readily at hand. The cohabitation with animals brought various advantages that drastically changed the human lifestyle but simultaneously led to the emergence of new epidemics. The majority of human pathogens known so far are zoonotic diseases and the development of both agricultural practices and human activities have provided new dynamics for transmission. This article provides a general overview of some factors that influence the epidemic potential of a zoonotic disease, Q fever. As an example of a disease where the interaction between the environment, animal (domestic or wildlife) and human populations determines the likelihood of the epidemic potential, the management of infection due to the Q fever agent, Coxiella burnetii, provides an interesting model for the application of the holistic One Health approach.
Quantification of Mycobacterium bovis transmission in a badger vaccine field trial
Aznar, I. ; Frankena, K. ; More, S.J. ; O'Keeffe, J. ; McGrath, G. ; Jong, M.C.M. de - \ 2018
Preventive Veterinary Medicine 149 (2018). - ISSN 0167-5877 - p. 29 - 37.
Bacille calmette-Guérin (BCG) - Badgers - Basic reproduction ratio - Mycobacterium bovis - Transmission - Vaccine efficacy for infectiousness - Vaccine efficacy for susceptibility
In the UK and Ireland, Bacille Calmette-Guérin (BCG) vaccination of badgers has been suggested as one of a number of strategies to control or even eradicate Mycobacterium bovis infection in badgers. In this manuscript, we present the results of a badger field trial conducted in Ireland and discuss how the novel trial design and analytical methods allowed the effects of vaccination on protection against infection and, more importantly, on transmission to be estimated. The trial area was divided into three zones North to South (A, B and C) where vaccination coverages of 0, 50 and 100%, respectively, were applied. Badgers were trapped over a 4 year period. Badgers were assigned to either placebo or vaccine treatment, with treatment allocation occurring randomly in zone B. Blood samples were collected at each capture, and serology was performed in these samples using a chemiluminescent multiplex ELISA system (Enfer test). The analysis aimed to compare new infections occurring in non-infected non-vaccinated badgers to those in non-infected vaccinated ones, while accounting for the zone in which the badger was trapped and the infection pressure to which this individual badger was exposed. In total, 440 records on subsequent trappings of individual non-infected badgers were available for analysis. Over the study period, 55 new infections occurred in non-vaccinated (out of 239 = 23.0%) and 40 in vaccinated (out of 201 = 19.9%) badgers. A Generalized Linear Model (GLM) with a cloglog link function was used for analysis. Statistical analysis showed that susceptibility to natural exposure with M. bovis was reduced in vaccinated compared to placebo treated badgers: vaccine efficacy for susceptibility, VES, was 59% (95% CI = 6.5%–82%). However, a complete lack of effect from BCG vaccination on the infectivity of vaccinated badgers was observed, i.e. vaccine efficacy for infectiousness (VEI) was 0%. Further, the basic reproduction ratio as a function of vaccination coverage (p) (i.e. R(p)) was estimated. Given that the prevalence of M. bovis infection in badgers in endemic areas in Ireland is approximately 18%, we estimated the reproduction ratio in the unvaccinated population as R(0) = 1.22. Because VES was now known, the reproduction ratio for a fully vaccinated population was estimated as R(1) = 0.50. These results imply that with vaccination coverage in badgers exceeding 30%, eradication of M. bovis in badgers in Ireland is feasible, provided that the current control measures also remain in place.
Vector competence of northern and southern European Culex pipiens pipiens mosquitoes for West Nile virus across a gradient of temperatures
Vogels, C.B.F. ; Göertz, G.P. ; Pijlman, G.P. ; Koenraadt, C.J.M. - \ 2017
Medical and Veterinary Entomology 31 (2017)4. - ISSN 0269-283X - p. 358 - 364.
Arbovirus - Culex pipiens complex - Infection - Italy - Northern house mosquito - The Netherlands - Transmission

In Europe, West Nile virus (WNV) outbreaks have been limited to southern and central European countries. However, competent mosquito vectors and susceptible bird hosts are present in northern Europe. Differences in temperature and vector competence of mosquito populations may explain the absence of WNV outbreaks in northern Europe. The aim of the present study was to directly compare vector competence of northern and southern European Culex pipiens (Cx. p.) pipiens mosquitoes for WNV across a gradient of temperatures. WNV infection and transmission rates were determined for two Cx. p. pipiens populations originating from The Netherlands and Italy, respectively. Mosquitoes were orally exposed by providing an infectious bloodmeal, or by injecting WNV (lineage 2) in the thorax, followed by 14-day incubation at 18, 23, or 28°C. No differences in infection or transmission rates were found between the Cx. p. pipiens populations with both infection methods, but WNV transmission rates were significantly higher at temperatures above 18°C. The absence of WNV outbreaks in northern Europe cannot be explained by differences in vector competence between Cx. p. pipiens populations originating from northern and southern Europe. This study suggests that low temperature is a key limiting factor for WNV transmission.

Transmissible mycobacterium tuberculosis strains share genetic markers and immune phenotypes
Nebenzahl-Guimaraes, Hanna ; Laarhoven, Arjan van; Farhat, Maha R. ; Koeken, Valerie A.C.M. ; Mandemakers, Jornt J. ; Zomer, Aldert ; Hijum, Sacha A.F.T. Van; Netea, Mihai G. ; Murray, Megan ; Crevel, Reinout van; Soolingen, Dick van - \ 2017
American Journal of Respiratory and Critical Care Medicine 195 (2017)11. - ISSN 1073-449X - p. 1519 - 1527.
Bacterial genomes - Immunology - Transmission - Tuberculosis

Rationale: Successful transmission of tuberculosis depends on the interplay of human behavior, host immune responses, and Mycobacterium tuberculosis virulence factors. Previous studies have been focused on identifying host risk factors associated with increased transmission, but the contribution of specific genetic variations in mycobacterial strains themselves are still unknown. Objectives: To identify mycobacterial genetic markers associated with increased transmissibility and to examine whether these markers lead to altered in vitro immune responses. Methods: Using a comprehensive tuberculosis registry (n = 10,389) and strain collection in the Netherlands, we identified a set of 100 M. tuberculosis strains either least or most likely to be transmitted after controlling for host factors.Wesubjected these strains to wholegenome sequencing and evolutionary convergence analysis, and we repeated this analysis in an independent validation cohort. We then performed immunological experiments to measure in vitro cytokine production and neutrophil responses to a subset of the original strains with or without the identified mutations associated with increased transmissibility. Measurements and Main Results: We identified the loci espE, PE-PGRS56, Rv0197, Rv2813-2814c, and Rv2815-2816c as targets of convergent evolution among transmissible strains. We validated four of these regions in an independent set of strains, and we demonstrated that mutations in these targets affected in vitro monocyte and T-cell cytokine production, neutrophil reactive oxygen species release, and apoptosis. Conclusions: In this study, we identified genetic markers in convergent evolution of M. tuberculosis toward enhanced transmissibility in vivo that are associated with altered immune responses in vitro.

Competitive exclusion reduces transmission and excretion of extended-spectrum-β-lactamase-producing Escherichia coli in broilers
Ceccarelli, Daniela ; Essen-Zandbergen, Alieda van; Smid, Bregtje ; Veldman, Kees T. ; Boender, Gert Jan ; Fischer, Egil A.J. ; Mevius, Dik J. ; Goot, Jeanet A. van der - \ 2017
Applied and Environmental Microbiology 83 (2017)11. - ISSN 0099-2240 - 13 p.
Broiler chicken - Competitive exclusion - ESBL - Escherichia coli - Excretion - Intervention - Poultry - Transmission - β-lactamases

Extended-spectrum β-lactamases (ESBLs) and plasmid-mediated AmpC β-lactamases (pAmpC) are enzymes able to hydrolyze a large variety of β-lactam antibiotics, including third-generation cephalosporins and monobactams. Broilers and broiler meat products can be highly contaminated with ESBL- and pAmpCproducing Escherichia coli strains, also known as extended-spectrum cephalosporin (ESC)-resistant E. coli strains, and can be a source for human infections. As few data on interventions to reduce the presence of ESC-resistant E. coli in broilers are available, we used transmission experiments to examine the role of competitive exclusion (CE) on reducing transmission and excretion in broilers. A broiler model to study the transmission of ESC-resistant E. coli was set up. Day-old chickens were challenged with an ESBL-producing E. coli strain isolated from healthy broilers in the Netherlands. Challenged and not challenged chicks were housed together in pairs or in groups, and ESBL-producing E. coli transmission was monitored via selective culturing of cloacal swab specimens. We observed a statistically significant reduction in both the transmission and excretion of ESBL-producing E. coli in chicks treated with the probiotic flora before E. coli challenge compared to the transmission and excretion in untreated controls. In conclusion, our results support the use of competitive exclusion as an intervention strategy to control ESC-resistant E. coli in the field.

Predicting the ability of preclinical diagnosis to improve control of farm-to-farm foot-and-mouth disease transmission in cattle
Nelson, Noel ; Paton, David J. ; Gubbins, Simon ; Colenutt, Claire ; Brown, Emma ; Hodgson, Sophia ; Gonzales Rojas, Jose - \ 2017
Journal of Clinical Microbiology 55 (2017)6. - ISSN 0095-1137 - p. 1671 - 1681.
Diagnostics - Early detection - FMD - Foot-and-mouth disease virus - PCR - Sensitivity - Surveillance - Transmission

Foot-and-mouth disease (FMD) can cause large disruptive epidemics in livestock. Current eradication measures rely on the rapid clinical detection and removal of infected herds. Here, we evaluated the potential for preclinical diagnosis during reactive surveillance to reduce the risk of between-farm transmission. We used data from transmission experiments in cattle where both samples from individual animals, such as blood, probang samples, and saliva and nasal swabs, and herd-level samples, such as air samples, were taken daily during the course of infection. The sensitivity of each of these sample types for the detection of infected cattle during different phases of the early infection period was quantified. The results were incorporated into a mathematical model for FMD, in a cattle herd, to evaluate the impact of the early detection and culling of an infected herd on the infectious output. The latter was expressed as the between-herd reproduction ratio, Rh, where an effective surveillance approach would lead to a reduction in the Rh value to <1. Applying weekly surveillance, clinical inspection alone was found to be ineffective at blocking transmission. This was in contrast to the impact of weekly random sampling (i.e., using saliva swabs) of at least 10 animals per farm or daily air sampling (housed cattle), both of which were shown to reduce the Rh to <1. In conclusion, preclinical detection during outbreaks has the potential to allow earlier culling of infected herds and thereby reduce transmission and aid the control of epidemics.

Using a ray-tracing model to design a greenhouse with maximized transmission during winter
Swinkels, G.L.A.M. ; Kempkes, F.L.K. ; Hemming, S. - \ 2017
Acta Horticulturae 1154 (2017). - ISSN 0567-7572 - p. 179 - 183.
Greenhouse - Model - Ray tracing - Transmission - Winter

During winter, natural light limits crop growth, and it is therefore important to use all the available sunlight for crop production. Important factors that influence light transmission are the structure of the greenhouse (construction elements, orientation, roof slope, symmetrical or asymmetrical design) and the greenhouse roof material (base material, coating(s), diffuse or clear). A project was started to maximize light transmission during winter by optimizing these factors. In the first phase of the project, a simulation model was used to analyze a number of promising new concepts. To validate the simulation model, a practical experiment with scale models in the open field was carried out. During winter, the transmission of these scale models was measured. Despite a number of factors that could not be controlled or modelled, such as rain and condensation, in general there was a good match between measured and calculated values. As an overall conclusion, the simulation model showed no consistent differences from the measurements. An asymmetric cover (saw tooth) in combination with diffuse glass did not contribute significantly to light transmission in comparison with a Venlo type cover. This supported the decisions made during the design of the final full-scale demonstration greenhouse in the follow-up project.

Mutations in the haemagglutinin protein and their effect in transmission of highly pathogenic avian influenza (HPAI) H5N1 virus in sub-optimally vaccinated chickens
Sitaras, Ioannis ; Rousou, Xanthoula ; Peeters, Ben ; Jong, Mart C.M. de - \ 2016
Vaccine 34 (2016)46. - ISSN 0264-410X - p. 5512 - 5518.
Epidemiology - H5N1 - HA - Influenza - Mutations - Transmission - Vaccination

Background Transmission of highly pathogenic avian influenza (HPAI) viruses in poultry flocks is associated with huge economic losses, culling of millions of birds, as well as human infections and deaths. In the cases where vaccination against avian influenza is used as a control measure, it has been found to be ineffective in preventing transmission of field strains. Reports suggest that one of the reasons for this is the use of vaccine doses much lower than the ones recommended by the manufacturer, resulting in very low levels of immunity. In a previous study, we selected for immune escape mutants using homologous polyclonal sera and used them as vaccines in transmission experiments. We concluded that provided a threshold of immunity is reached, antigenic distance between vaccine and challenge strains due to selection need not result in vaccine escape. Here, we evaluate the effect that the mutations in the haemagglutinin protein of our most antigenically-distant mutant may have in the transmission efficiency of this mutant to chickens vaccinated against the parent strain, under sub-optimal vaccination conditions resembling those often found in the field. Methods In this study we employed reverse genetics techniques and transmission experiments to examine if the HA mutations of our most antigenically-distant mutant affect its efficiency to transmit to vaccinated chickens. In addition, we simulated sub-optimal vaccination conditions in the field, by using a very low vaccine dose. Results We find that the mutations in the HA protein of our most antigenically-distant mutant are not enough to allow it to evade even low levels of vaccination-induced immunity. Discussion Our results suggest that – for the antigenic distances we investigated – vaccination can reduce transmission of an antigenically-distant strain compared to the unvaccinated groups, even when low vaccine doses are used, resulting in low levels of immunity.

Mass mosquito trapping for malaria control in western Kenya : Study protocol for a stepped wedge cluster-randomised trial
Hiscox, Alexandra ; Homan, Tobias ; Mweresa, Collins K. ; Maire, Nicolas ; Pasquale, Aurelio Di; Masiga, Daniel ; Oria, Prisca A. ; Alaii, Jane ; Leeuwis, Cees ; Mukabana, Wolfgang R. ; Takken, Willem ; Smith, Thomas A. - \ 2016
Trials 17 (2016). - ISSN 1745-6215
Anopheline mosquitoes - Clinical malaria - Mass trapping - Odour-baited trap - Stepped wedge cluster-randomised trial - Transmission - Vector control - 016-3956

Background: Increasing levels of insecticide resistance as well as outdoor, residual transmission of malaria threaten the efficacy of existing vector control tools used against malaria mosquitoes. The development of odour-baited mosquito traps has led to the possibility of controlling malaria through mass trapping of malaria vectors. Through daily removal trapping against a background of continued bed net use it is anticipated that vector populations could be suppressed to a level where continued transmission of malaria will no longer be possible. Methods/design: A stepped wedge cluster-randomised trial design was used for the implementation of mass mosquito trapping on Rusinga Island, western Kenya (the SolarMal project). Over the course of 2 years (2013-2015) all households on the island were provided with a solar-powered mosquito trapping system. A continuous health and demographic surveillance system combined with parasitological surveys three times a year, successive rounds of mosquito monitoring and regular sociological studies allowed measurement of intervention outcomes before, during and at completion of the rollout of traps. Data collection continued after achieving mass coverage with traps in order to estimate the longer term effectiveness of this novel intervention. Solar energy was exploited to provide electric light and mobile phone charging for each household, and the impacts of these immediate tangible benefits upon acceptability of and adherence to the use of the intervention are being measured. Discussion: This study will be the first to evaluate whether the principle of solar-powered mass mosquito trapping could be an effective tool for elimination of malaria. If proven to be effective, this novel approach to malaria control would be a valuable addition to the existing strategies of long-lasting insecticide-treated nets and case management. Sociological studies provide a knowledge base for understanding the usage of this novel tool.

Larvae of Ixodes ricinus transmit Borrelia afzelii and B. miyamotoi to vertebrate hosts
Duijvendijk, Gilian van; Coipan, Claudia ; Wagemakers, Alex ; Fonville, Manoj ; Ersöz, Jasmin ; Oei, Anneke ; Földvári, Gábor ; Hovius, Joppe ; Takken, Willem ; Sprong, Hein - \ 2016
Parasites & Vectors 9 (2016). - ISSN 1756-3305
Borrelia burgdorferi - Borrelia miyamotoi - Infection - Ixodes ricinus - Larva - Rodent - Tick - Transmission - Vector - 016-3918

Background: Lyme borreliosis is the most common tick-borne human disease and is caused by Borrelia burgdorferi sensu lato (s.l.). Borrelia miyamotoi, a relapsing fever spirochaete, is transmitted transovarially, whereas this has not been shown for B. burgdorferi (s.l). Therefore, B. burgdorferi (s.l) is considered to cycle from nymphs to larvae through vertebrates. Larvae of Ixodes ricinus are occasionally B. burgdorferi (s.l) infected, but their vector competence has never been studied. Methods: We challenged 20 laboratory mice with field-collected larvae of I. ricinus. A subset of these larvae was analysed for infections with B. burgdorferi (s.l) and B. miyamotoi. After three to four challenges, mice were sacrificed and skin and spleen samples were analysed for infection by PCR and culture. Results: Field-collected larvae were naturally infected with B. burgdorferi (s.l) (0.62 %) and B. miyamotoi (2.0 %). Two mice acquired a B. afzelii infection and four mice acquired a B. miyamotoi infection during the larval challenges. Conclusion: We showed that larvae of I. ricinus transmit B. afzelii and B. miyamotoi to rodents and calculated that rodents have a considerable chance of acquiring infections from larvae compared to nymphs. As a result, B. afzelii can cycle between larvae through rodents. Our findings further imply that larval bites on humans, which easily go unnoticed, can cause Lyme borreliosis and Borrelia miyamotoi disease.

Aerosol transmission of foot-and-mouth disease virus Asia-1 under experimental conditions
Colenutt, C. ; Gonzales, J.L. ; Paton, D.J. ; Gloster, J. ; Nelson, N. ; Sanders, C. - \ 2016
Veterinary Microbiology 189 (2016). - ISSN 0378-1135 - p. 39 - 45.
Aerosol - Exposure dose - Foot-and-mouth disease virus - Transmission
Foot-and-mouth disease virus (FMDV) control measures rely on understanding of virus transmission mechanisms. Direct contact between naïve and infected animals or spread by contaminated fomites is prevented by quarantines and rigorous decontamination procedures during outbreaks. Transmission of FMDV by aerosol may not be prevented by these control measures and this route of transmission may allow infection of animals at distance from the infection source. Understanding the potential for aerosol spread of specific FMDV strains is important for informing control strategies in an outbreak. Here, the potential for transmission of an FMDV Asia 1 strain between pigs and cattle by indirect aerosol exposure was evaluated in an experimental setting. Four naïve calves were exposed to aerosols emitted from three infected pigs in an adjacent room for a 10 h period. Direct contact between pigs and cattle and fomite transfer between rooms was prevented. Viral titres in aerosols emitted by the infected pigs were measured to estimate the dose that calves were exposed to. One of the calves developed clinical signs of FMD, whilst there was serological evidence for spread to cattle by aerosol transmission in the remaining three calves. This highlights the possibility that this FMDV Asia 1 strain could be spread by aerosol transmission given appropriate environmental conditions should an outbreak occur in pigs. Our estimates suggest the exposure dose required for aerosol transmission was higher than has been previously quantified for other serotypes, implying that aerosols are less likely to play a significant role in transmission and spread of this FMDV strain
Co-housing of Rift Valley fever virus infected lambs with immunocompetent or immunosuppressed lambs does not result in virus transmission
Wichgers Schreur, Paul J. ; Keulen, Lucien Van; Kant, Jet ; Oreshkova, Nadia ; Moormann, Rob J.M. ; Kortekaas, Jeroen - \ 2016
Frontiers in Microbiology 7 (2016). - ISSN 1664-302X
Contact-exposure - Epidemiology - Horizontal transmission - Rift Valley fever virus - Risk assessment - Transmission

Rift Valley fever virus (RVFV) is transmitted among susceptible animals by mosquito vectors. Although the virus can be isolated from nasal and oral swabs of infected animals and is known to be highly infectious when administered experimentally via oral or respiratory route, horizontal transmission of the virus is only sporadically reported in literature. We considered that immunosuppression resulting from stressful conditions in the field may increase the susceptibility to horizontally transmitted RVFV. Additionally, we reasoned that horizontal transmission may induce immune responses that could affect the susceptibility of contact-exposed animals to subsequent infection via mosquito vectors. To address these two hypotheses, viremic lambs were brought into contact with sentinel lambs. One group of sentinel lambs was treated with the immunosuppressive synthetic glucocorticosteroid dexamethasone and monitored for signs of disease and presence of virus in the blood and target organs. Another group of contact-exposed sentinel lambs remained untreated for three weeks and was subsequently challenged with RVFV. We found that none of the dexamethasone-treated contact-exposed lambs developed detectable viremia, antibody responses or significant increases in cytokine mRNA levels. Susceptibility of immunocompetent lambs to RVFV infection was not influenced by previous contact-exposure. Our results are discussed in light of previous findings.

Foot-and-mouth Disease Transmission in Africa : Implications for Control, a Review
Tekleghiorghis, T. ; Moormann, R.J.M. ; Weerdmeester, K. ; Dekker, A. - \ 2016
Transboundary and Emerging Diseases 63 (2016)2. - ISSN 1865-1674 - p. 136 - 151.
Africa - Animal husbandry - Foot-and-mouth disease - Serotype - Topotype - Transmission - Wildlife

In Africa, for the control of foot-and-mouth disease (FMD), more information is needed on the spread of the disease at local, regional and inter-regional level. The aim of this review is to identify the role that animal husbandry, trade and wildlife have on the transmission of FMD and to provide a scientific basis for different FMD control measures in Africa. Review of literature, published reports and databases shows that there is more long distance spread of FMD virus serotypes within North, West, Central and East Africa than in southern Africa. In North, West, Central and East Africa migratory animal husbandry systems often related with search for grazing and water as well as trade are practiced to a greater extent than in southern Africa. In southern Africa, the role of African buffalo (Syncerus caffer) is more extensively studied than in the other parts of Africa, but based on the densities of African buffalo in Central and East Africa, one would assume that buffalo should also play a role in the epidemiology of FMD in this part of Africa. More sampling of buffalo is necessary in West, Central and East Africa. The genetic analysis of virus strains has proven to be valuable to increase our understanding in the spread of FMD in Africa. This review shows that there is a difference in FMD occurrence between southern Africa and the rest of the continent; this distinction is most likely based on differences in animal husbandry and trade systems. Insufficient data on FMD in wildlife outside southern Africa is limiting our understanding on the role wildlife plays in the transmission of FMD in the other buffalo inhabited areas of Africa.

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