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Rais, Olivier

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Rais, Olivier
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Ancien.ne collaborateur.trice
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https://libra.unine.ch/handle/123456789/347

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  • 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
    Métadonnées seulement
    Borrelia burgdorferi genospecies detection by RLB hybridization in Ixodes cinus ticks from different sites of North-Eastern Poland
    (2014)
    Dunaj, Justyna
    ;
    Zajkowska, JM
    ;
    Kondrusik, M
    ;
    Gern, Lise 
    ;
    Rais, Olivier 
    ;
    Moniuszko, Anna
    ;
    Pancewicz, Slawomir
    ;
    Swierzbi?ska, R
  • Publication
    Métadonnées seulement
  • Publication
    Accès libre
  • Publication
    Accès libre
    Tick bites in a Lyme borreliosis highly endemic area in Switzerland
    (2009)
    Hügli, Delphine
    ;
    Moret, Jacqueline
    ;
    Rais, Olivier 
    ;
    Moosmann, Yves
    ;
    Erard, Philippe
    ;
    Malinverni, Raffaele 
    ;
    Gern, Lise 
    The duration of tick feeding is an important indicator to evaluate the risk of Borrelia burgdorferi sensu lato transmission, which increases considerably with the blood meal duration. This blood meal duration may be estimated from scutal index, the ratio between body length (idiosoma) and scutum width. For the estimation of blood meal duration in Ixodes ricinus, nymphal and adult female ticks were detached at predetermined intervals (24, 48, 72, and 96 h) from laboratory mice and rabbits and their scutal index calculated. From this, non-linear regression equations were developed to determine the duration of attachment for nymphal and adult female I. ricinus ticks. As part of an epidemiological study addressing the risk of subclinical (seroconversion) and clinical infections after a tick bite in the Neuchâtel area (Switzerland) over 3 years (2003–2005), duration of tick attachment and anatomical site of bites collected on participants as well as seasonal distribution of tick bites were studied. Tick attachment duration was estimated in all ticks collected during this study (n=261). Nymphs were attached for a mean (± standard error, SE) of 31.6 h (±2.6) and females for a mean (±SE) of 29.6 h (±3.2). Most nymphs were removed after 24 h of blood meal whereas most females were removed before 24 h. Legs were the major anatomical sites of bites for women (40.7%), men (44.4%), and almost all age classes. Only children <10 years old were bitten more frequently on the head (41.2%) and on the neck (38.5%) than participants >10 years. The majority of tick bites were recorded from May to July during the 3 years. Attachment sites can influence the discovery of ticks, hence the duration of the tick bite. A detailed body examination after each outing in forest and an early withdrawal of an attached tick is an effective way to prevent Lyme borreliosis.
  • Publication
    Métadonnées seulement
    Identification of host bloodmeal source and Borrelia burgdorferi sensu lato in field-collected Ixodes ricinus ticks in Chaumont (Switzerland)
    (2007)
    Cadenas, Francisca Moran
    ;
    Rais, Olivier 
    ;
    Humair, Pierre-François
    ;
    Douet, Véronique 
    ;
    Moret, Jacqueline
    ;
    Gern, Lise 
    To evaluate the importance of vertebrate species as tick hosts and as reservoir hosts in two endemic areas for Lyme borreliosis in Switzerland, we applied molecular methods for the analysis of bloodmeal source and Borrelia infection in questing Ixodes ricinus L. ticks. In total, 1,326 questing ticks were simultaneously analyzed for Borrelia and for blood meal remnants by using reverse line blot. An overall infection prevalence of 19.0% was recorded for Borrelia sp., with similar rates in both sites. Using a newly developed method for the analysis of bloodmeal targeting the 12S rDNA mitochondrial gene, identification of host DNA from field-collected ticks was possible in 43.6% of cases. Success of host identification at the genus and species level reached 72%. In one site, host identification success reached its maximum in spring (93% in May), decreasing in summer (20% in July) and rising in autumn (73% in October). In the other site, identification rate in ticks remained low from April to July and increased in autumn reaching 68% in October and November. The most prevalent identified host DNA was artiodactyls in both sites. Red squirrel DNA was significantly more frequently detected in ticks collected in one site, whereas insectivore DNA was more frequent in ticks in the other site. DNA from more than one vertebrate host was detected in 19.5% of nymphs and 18.9% of adults. Host DNA was identified in 48.4% of the Borrelia infected ticks. Although DNA from all Borrelia species was found in at least some ticks with DNA from mammals and some ticks with DNA from birds, our results confirm a general association of B. afzelii and B. burgdorferi sensu stricto with rodents, and B. valaisiana and B. garinii with birds.
  • Publication
    Métadonnées seulement
    Phenology of Ixodes ricinus and infection with Borrelia burgdorferi sensu lato along a North- and South-facing altitudinal gradient on Chaumont Mountain, Switzerland
    (2007)
    Cadenas, Francisca Moran
    ;
    Rais, Olivier 
    ;
    Jouda, Fatima
    ;
    Douet, Véronique 
    ;
    Humair, Pierre-François
    ;
    Moret, Jacqueline
    ;
    Gern, Lise 
    Questing Ixodes ricinus L. ticks were collected monthly from 2003 to 2005 on the north- and south-facing slopes of Chaumont Mountain in Neuchatel, Switzerland, at altitudes varying from 620 to 1,070 in. On the south-facing slope, questing tick density was higher than on the north-facing slope, and it decreased with altitude. Density tended to increase with altitude on the north-facing slope. Saturation deficit values higher than 10 mmHg and lasting for >2 mo were often recorded on the south-facing slope, explaining seasonal patterns of questing tick activity. The overall prevalence of Borrelia burgdorferi sensu lato was 22.4%, and prevalence differed according to exposure and among years. No difference was noticed between nymphs and adults. Four Borrelia species were identified. Mixed infections were detected in 52 ticks, B. garinii and B. valaisiana (n = 21) and B. afzelii and B. burgdorferi s.s. (n = 20) were the most frequent associations observed. The density of infected ticks varied from 3.6 to 78.7 infected nymphs per 1 00 m(2) and from 0.6 to 16.9 infected adults per 100 m(2), both slopes combined. The study on the south-facing slope was a follow-up of a previous study carried out at the same location during 1999-2001. Comparison of climatic data between the two periods showed a marked increase in saturation deficit. Substantial differences in density and phenology of ticks also were observed. At high elevations, ticks were significantly more abundant during the current study. This can be explained by rising temperatures recorded during summer at altitude, reaching values similar to those registered in the first study beneath. At the lowest altitude, adults were significantly less abundant, probably due to long-lasting high saturation deficits that impaired nymphal survival. The density of Borrelia-infected ticks was higher than in the previous study.