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Voordouw, Maarten

Nom
Voordouw, Maarten
Affiliation principale
Fonction
Ancien.ne collaborteur.trice
Identifiants
https://libra.unine.ch/handle/123456789/375
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0000-0001-9384-0436

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  • Publication
    Accès libre
  • Publication
    Accès libre
    Cross-immunity and community structure of a multiple-strain pathogen in the tick vector
    (2015-11)
    Durand, Jonas 
    ;
    Jacquet, Maxime 
    ;
    Paillard, Lye 
    ;
    Rais, Olivier 
    ;
    Gern, Lise 
    ;
    Voordouw, Maarten 
    Many vector-borne pathogens consist of multiple strains that circulate in both the vertebrate host and the arthropod vector. Characterization of the community of pathogen strains in the arthropod vector is therefore important for understanding the epidemiology of mixed vector-borne infections. Borrelia afzelii and B. garinii are two species of tick-borne bacteria that cause Lyme disease in humans. These two sympatric pathogens use the same tick, Ixodes ricinus, but are adapted to different classes of vertebrate hosts. Both Borrelia species consist of multiple strains that are classified using the highly polymorphic ospC gene. Vertebrate cross-immunity against the OspC antigen is predicted to structure the community of multiple-strain Borrelia pathogens. Borrelia isolates were cultured from field-collected I. ricinus ticks over a period spanning 11 years. The Borrelia species of each isolate was identified using a reverse line blot (RLB) assay. Deep sequencing was used to characterize the ospC communities of 190 B. afzelii isolates and 193 B. garinii isolates. Infections with multiple ospC strains were common in ticks, but vertebrate cross-immunity did not influence the strain structure in the tick vector. The pattern of genetic variation at the ospC locus suggested that vertebrate cross-immunity exerts strong selection against intermediately divergent ospC alleles. Deep sequencing found that more than 50% of our isolates contained exotic ospC alleles derived from other Borrelia species. Two alternative explanations for these exotic ospC alleles are cryptic coinfections that were not detected by the RLB assay or horizontal transfer of the ospC gene between Borrelia species.
  • Publication
    Accès libre
    Serological signature of tick-borne pathogens in Scandinavian brown bears over two decades
    (2015-7-28)
    Paillard, Lye 
    ;
    Jones, Krista L.
    ;
    Evans, Alina L.
    ;
    Jacquet, Maxime 
    ;
    Berret, Jérémy 
    ;
    Lienhard, Reto
    ;
    Bouzelboudjen, Mahmoud 
    ;
    Arnemo, Jon M.
    ;
    Swenson, Jon E.
    ;
    Voordouw, Maarten 
    Background: Anthropogenic disturbances are changing the geographic distribution of ticks and tick-borne diseases. Over the last few decades, the tick Ixodes ricinus has expanded its range and abundance considerably in northern Europe. Concurrently, the incidence of tick-borne diseases, such as Lyme borreliosis and tick-borne encephalitis, has increased in the human populations of the Scandinavian countries. Methods: Wildlife populations can serve as sentinels for changes in the distribution of tick-borne diseases. We used serum samples from a long-term study on the Scandinavian brown bear, Ursus arctos, and standard immunological methods to test whether exposure to Borrelia burgdorferi sensu lato, the causative agent of Lyme borreliosis, and tick-borne encephalitis virus (TBEV) had increased over time. Bears had been sampled over a period of 18 years (1995-2012) from a southern area, where Ixodes ricinus ticks are present, and a northern area where ticks are uncommon or absent. Results: Bears had high levels of IgG antibodies against B. burgdorferi sensu lato but not TBEV. Bears at the southern area had higher values of anti-Borrelia IgG antibodies than bears at the northern area. Over the duration of the study, the value of anti-Borrelia IgG antibodies increased in the southern area but not the northern area. Anti-Borrelia IgG antibodies increased with the age of the bear but declined in the oldest age classes. Conclusions: Our study is consistent with the view that ticks and tick-borne pathogens are expanding their abundance and prevalence in Scandinavia. Long-term serological monitoring of large mammals can provide insight into how anthropogenic disturbances are changing the distribution of ticks and tick-borne diseases.
  • Publication
    Accès libre
    Borrelia burgdorferi Has Minimal Impact on the Lyme Disease Reservoir Host Peromyscus leucopus
    (2011)
    Schwanz, Lisa E.
    ;
    Voordouw, Maarten 
    ;
    Brisson, Dustin
    ;
    Ostfeld, Richard S.
    The epidemiology of vector-borne zoonotic diseases is determined by encounter rates between vectors and hosts. Alterations to the behavior of reservoir hosts caused by the infectious agent have the potential to dramatically alter disease transmission and human risk. We examined the effect of Borrelia burgdorferi, the etiological agent of Lyme disease, on one of its most important reservoir hosts, the white-footed mouse, Peromyscus leucopus. We mimic natural infections in mice using the vector (Black-legged ticks, Ixodes scapularis) and examine the immunological and behavioral responses of mouse hosts. Despite producing antibodies against B. burgdorferi, infected mice did not have elevated white blood cells compared with uninfected mice. In addition, infected and uninfected mice did not differ in their wheel-running activity. Our results suggest that infection with the spirochete B. burgdorferi has little impact on the field activity of white-footed mice. Lyme disease transmission appears to be uncomplicated by pathogen-altered behavior of this reservoir host.
  • Publication
    Accès libre
    Prevalence of the pathogenic chytrid fungus, Batrachochytrium dendrobatidis, in an endangered population of northern leopard frogs, Rana pipiens
    (2010)
    Voordouw, Maarten 
    ;
    Adama, Doug
    ;
    Houston, Barb
    ;
    Govindarajulu, Purnima
    ;
    Robinson, John

    Background
    Emerging infectious diseases threaten naïve host populations with extinction. Chytridiomycosis, an emerging infectious disease of amphibians, is caused by the pathogenic fungus Batrachochytrium dendrobatidis (Bd) and has been linked to global declines in amphibians.
    Results
    We monitored the prevalence of Bd for four years in the Northern leopard frog, Rana pipiens, which is critically imperiled in British Columbia (BC), Canada. The prevalence of Bd initially increased and then remained constant over the last three years of the study. Young of the year emerging from breeding ponds in summer were rarely infected with Bd. Some individuals cleared their Bd infections and the return rate between infected and uninfected individuals was not significantly different.
    Conclusions
    The BC population of R. pipiens appears to have evolved a level of resistance that allows it to co-exist with Bd. However, this small population of R. pipiens remains vulnerable to extinction.
  • Publication
    Accès libre
    Rodent malaria-resistant strains of the mosquito, Anopheles gambiae, have slower population growth than -susceptible strains
    (2009)
    Voordouw, Maarten 
    ;
    Anholt, Bradley R.
    ;
    Taylor, Pam J.
    ;
    Hurd, Hilary
    Background
    Trade-offs between anti-parasite defence mechanisms and other life history traits limit the evolution of host resistance to parasites and have important implications for understanding diseases such as malaria. Mosquitoes have not evolved complete resistance to malaria parasites and one hypothesis is that anti-malaria defence mechanisms are costly.
    Results
    We used matrix population models to compare the population growth rates among lines of Anopheles gambiae that had been selected for resistance or high susceptibility to the rodent malaria parasite, Plasmodium yoelii nigeriensis. The population growth rate of the resistant line was significantly lower than that of the highly susceptible and the unselected control lines, regardless of whether mosquitoes were infected with Plasmodium or not. The lower population growth of malaria-resistant mosquitoes was caused by reduced post blood-feeding survival of females and poor egg hatching.
    Conclusions
    With respect to eradicating malaria, the strategy of releasing Plasmodium-resistant Anopheles mosquitoes is unlikely to be successful if the costs of Plasmodium-resistance in the field are as great as the ones measured in this study. High densities of malaria-resistant mosquitoes would have to be maintained by continuous release from captive breeding facilities.
  • Publication
    Accès libre
    Comparison of male reproductive success in malaria-refractory and susceptible strains of Anopheles gambiae
    (2008)
    Voordouw, Maarten 
    ;
    Koella, Jacob 
    ;
    Hurd, Hilary
    Background
    In female mosquitoes that transmit malaria, the benefits of being refractory to the Plasmodium parasite are balanced by the immunity costs in the absence of infection. Male mosquitoes, however, gain no advantage from being refractory to blood-transmitted parasites, so that any costs associated with an enhanced immune system in the males limit the evolution of female refractoriness and has practical implications for the release of transgenic males.
    Methods
    Aspects of the male cost of carrying Plasmodium-refractory genes were estimated by comparing the males' immune response and reproductive success among strains of Anopheles gambiae that had been selected for refractoriness or extreme susceptibility to the rodent malaria parasite, Plasmodium yoelii nigeriensis. The refractory males had a stronger melanization response than males from the susceptible line. Four traits were used as correlates of a male's reproductive success: the proportion of females that were inseminated by a fixed number of males in a cage within a fixed time frame, the proportion of females with motile sperm in their spermathecae, the proportion of ovipositing females, and the mean number of eggs per batch.
    Results
    Although there were significant differences among groups of males in sperm motility and oviposition success, these differences in male reproductive success were not associated with the refractory or susceptible male genotypes. Contrary to expectation, females mated to early emerging refractory males laid significantly more eggs per batch than females mated to later emerging susceptible males. Sperm motility and oviposition success were strongly correlated suggesting that variation in sperm motility influences female oviposition and ultimately male reproductive success.
    Conclusions
    An increased melanization response in male A. gambiae does not diminish male reproductive success under the experimental protocol used in this study. That refractory males induced ovipositing females to lay more eggs than susceptible males is an interesting result for any strategy considering the release of transgenic males. That sperm motility influences female oviposition is also important for the release of transgenic males.
  • Publication
    Accès libre
    No maternal effects after stimulation of the melanization response in the yellow fever mosquito Aedes aegypti
    (2008)
    Voordouw, Maarten 
    ;
    Lambrechts, Louis
    ;
    Koella, Jacob 
    The costs and benefits of activating the immune system can reach across generations. Thus, in vertebrates and in several invertebrates, stimulating the immune system of a female can enhance immunity of her offspring or decrease offspring fitness. We evaluated the potential maternally transmitted costs and benefits of the melanization response, an innate immune response of insects that helps to protect mosquitoes from malaria parasites. We manipulated the maternal melanization response of the yellow fever mosquito Aedes aegypti by inoculating female mosquitoes with negatively charged sephadex beads or with immunologically inert glass beads; a control group was not inoculated. In the next generation, we assayed the melanization response and measured three other life-history traits: survival up to emergence, the age at emergence, and body size (estimated as wing length). We found no evidence of fitness costs or benefits for the offspring. A retrospective power analysis found that our experiment would have detected an effect size that is three times smaller than the maternal immune priming effects that have been reported in the literature. We did find a strong correlation between offspring wing length and melanization response. Overall, our findings indicate that trans-generational immune priming in invertebrates cannot be generalized, and that it may depend on the species, the immune challenge, and the environmental conditions.
  • Publication
    Accès libre
    Genetic variation in the primary sex ratio in populations of the intertidal copepod, Tigriopus californicus, is widespread on Vancouver Island
    (2008)
    Voordouw, Maarten 
    ;
    Stebbins, Gabe
    ;
    Robinson, H. Eve
    ;
    Perrot-Minnot, Marie-Jeanne
    ;
    Rigaud, Thierry
    ;
    Anholt, Bradley R
    Hypothesis: Genetic variation for the primary sex ratio is widespread in a copepodwith polygenic sex determination. Cytoplasmic sex ratio distorters (e.g. Wolbachia andmicrosporidians) influence the primary sex ratio in this copepod.
    Organism: The intertidal copepod, Tigriopus californicus; six populations from VancouverIsland, British Columbia.
    Study site: Quantitative genetics experiment in the laboratory. PCR and antibioticsexperiment to test for the presence of cytoplasmic sex ratio distorters.
    Results: Genetic variation for the primary sex ratio was found in five of the six populationssurveyed. The primary sex ratio was paternally transmitted. There was no evidence thatWolbachia or microsporidians influenced the primary sex ratio of T. californicus.
  • Publication
    Accès libre
    Intra-specific variation of sperm length in the malaria vector Anopheles gambiae: males with shorter sperm have higher reproductive success
    (2008)
    Voordouw, Maarten 
    ;
    Koella, Jacob 
    ;
    Hurd, Hilary
    Background
    Intra-specific variation in sperm length influences male reproductive success in several species of insects. In males of the malaria vector Anopheles gambiae, sperm length is highly variable but the significance of this variation is unknown. Understanding what determines the reproductive success of male mosquitoes is critical for controlling malaria, and in particular for replacing natural populations with transgenic, malaria-resistant mosquitoes.
    Methods
    A laboratory population of A. gambiae males was tested for intra-specific variation in sperm length. A full-sib quantitative genetic design was used to test for a genetic component of sperm length in A. gambiae males and estimate its heritability. This study also tested for a relationship between sperm length and male reproductive success in A. gambiae. Male reproductive success was measured as the proportions of inseminated and ovipositing females.
    Results
    There was intra-specific variation of sperm length in A. gambiae. There was no significant genetic variation in sperm length and its heritability was low (h2 = 0.18) compared to other insects. Sperm length was correlated with male body size (measured as wing length). Males with short sperm had significantly higher reproductive success than males with long sperm and this was independent of body size.
    Conclusions
    This is the first study to demonstrate intra-specific variation in sperm length in A. gambiae and that males with short sperm have higher reproductive success. That sperm length influences female oviposition is important for any strategy considering the release of transgenic males.