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Gern, Lise

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Gern, Lise
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Ancien.ne collaborateur.trice
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https://libra.unine.ch/handle/123456789/303

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  • Publication
    Accès libre
    Ecologie de 'Borrelia burgdorferi' sensu lato en Suisse: dynamique saisonnière de la tique 'Ixodes ricinus', sa relation avec les rongeurs, et implication des modes de transmission de 'B. afzelii' entre rongeurs et tiques sur la diversité du gène ospC chez 'B.afzelii'
    (2012)
    Pérez Bertoni, David
    ;
    Gern, Lise 
    En Europe, les agents de la Borréliose de Lyme (BL) sont maintenus dans la nature via un cycle de transmission impliquant la tique Ixodes ricinus (I. ricinus) et des hôtes réservoirs. Le gène codant pour l’ « Outer Surface Protein C » (OspC), une lipoprotéine plasmidique exprimée par les spirochètes lors du repas sanguin de la tique et lors de la dissémination chez l’hôte, est un marqueur génétique pouvant être associé à la pathogénèse et à la sévérité d’une BL. L’analyse du gène ospC a permis de classifier des isolats de Borrelia. burgdorferi sensu lato (B. burgdorferi sl) en groupes ospC.
    De 2003 à 2005, nous avons prélevé de façon mensuelle des tiques libres dans 2 sites du plateau suisse, les Portes-Rouges (PR) et le Staatswald (SW). Parallèlement, les micromammifères ont été piégés afin de rechercher la présence de stades immatures d’I. ricinus et l’infection des rongeurs a été vérifiée par xénodiagnose. La typisation des génoespèces de B. burgdorferi sl chez les tiques libres, les tiques des rongeurs et les tiques de xénodiagnose a été réalisée par « Polymerase Chain Reaction » (PCR) et « Restriction Fragment Length Polymorphism » (RFLP). Les isolats de B. afzelii, génoespèce associée aux rongeurs, obtenus de ces 3 populations de tiques, ont été analysés par « Single Stranded Conformational Polymorphism » (SSCP) et classifiés par groupes ospC.
    Nous avons observé durant les 3 années des variations dans l’évolution saisonnière de la densité de tiques libres. La densité de nymphes en quête était plus importante au PR alors que la proportion de rongeurs infestés par des stades immatures d’I. ricinus était similaire dans les 2 sites. Des tiques ont été observées sur les rongeurs en automne et en été alors que la densité de tiques libres était faible voire inexistante. Les rongeurs du SW présentaient des infestations par des immatures d’I. ricinus élevées et 28% étaient infestés par des nymphes et des larves (11% au PR). Cette nutrition simultanée de tiques regroupées sur un hôte porte le nom de co-feeding et permet la transmission de pathogènes entre tiques infectées et tiques non-infectées, sans présence d’infection systémique chez l’hôte. Malgré une situation favorable de co-feeding, principalement au SW, seul B. afzelii et B. bavariensis ont été transmises des rongeurs aux tiques laissant supposer que le co-feeding ne contribue pas au maintien de la diversité des génoespèces de B. burgdorferi sl présentes chez les tiques libres.
    L’analyse du gène ospC nous a permis de classer les isolats de B. afzelii provenant des différentes populations de tiques en 10 groupes ospC, dont 8 déjà décrits (A1, A2, A3, A4, A5, A6, A8, VS461) et 2 nouveaux (ME et YU). La plus grande diversité de groupes ospC a été observée chez les tiques en quête. Les isolats de B. afzelii obtenus à partir de larves d’I. ricinus s’étant nourries en co-feeding avec des nymphes présentaient une diversité de groupes ospC plus importante que celles s’étant nourries seules. Ce travail montre pour la première fois l’importance du co-feeding dans le maintien de la diversité intraspécifique de B. afzelii dans la nature.
  • Publication
    Accès libre
    A flea-induced pre-hatching maternal effect modulates tick feeding behaviour on great tit nestlings
    (2008)
    Gallizzi, K.
    ;
    Gern, Lise 
    ;
    Richner, H.
    1. A host's defence reaction against one parasite species can modulate the habitat quality for other parasites in two ways: it can provide cross-resistance against closely related species due to antigenic similarity, or it can reduce resistance to other cohabiting species, since the mounting of multiple defence reactions is more costly.
    2. Here we test whether two completely unrelated parasite species can influence each other across host generations, that is, whether a hen flea-induced maternal effect known to protect great tit (Parus major) nestlings against flea infestations will also alter tick (Ixodes ricinus) feeding behaviour on nestlings.
    3. We infested experimental great tit nests with hen fleas (Ceratophyllus gallinae) prior to egg-laying to induce the maternal effect, while all parasites were removed in control nests. Nestlings from the two types of nests were then cross-fostered into flea-free foster nests to produce broods that contained both, nestlings with and without the flea-induced maternal effect. Five days after hatching, we put five larval ticks on each nestling and assessed tick feeding behaviour.
    4. We found that ticks feeding on nestlings with the flea-induced maternal effect detached significantly earlier than ticks feeding on controls. The result is compatible with the hypothesis of a trans-generational parasite–parasite interaction, that is, it suggests that the flea-induced maternal effect alters tick feeding behaviour and that it may protect nestlings against tick-borne diseases by reducing tick attachment times. In addition, we found that more ticks attached on male than on female nestlings, suggesting that males are more susceptible to parasites than females as shown in other vertebrates.
  • Publication
    Accès libre
    Ixodes ricinus Density, and Distribution and Prevalence of Borrelia burgdorferi Sensu Lato Infection Along an Altitudinal Gradient
    (2004)
    Jouda, Fatima
    ;
    Perret, Jean-Luc
    ;
    Gern, Lise 
    In this study, we measured the phenology of Ixodes ricinus ticks and their infection with Borrelia burgdorferi sensu lato (sl) simultaneously along an altitudinal gradient to assess the impact of climate on the phenology of ticks and on their infection with B. burgdorferi sl. From 1999 to 2001, free-living I. ricinus ticks were collected monthly by flagging vegetation at three different altitudes (620, 740, and 900 m above sea level) on the slope of a mountain in Chaumont (Neuchâtel, Switzerland). I. ricinus ticks were examined for the presence of B. burgdorferi sl by using direct fluorescent antibody assay and isolation of spirochetes. Borrelia species were characterized by polymerase chain reaction followed by restriction fragment-length polymorphism. Tick density and tick phenology varied with altitude. Although the peak tick density decreased and the onset of ticks was delayed with altitude, the phenology was much more stable among years at the highest altitudes than at the lowest. The prevalence of B. burgdorferi infection in nymphs and adults decreased with altitude. The prevalence of infection differed significantly among years, and it was significantly higher in adults (30%) than in nymphs (21%). B. burgdorferi infection in adults was positively related with adult density, but this was not observed for nymphs. Five B. burgdorferi sl genospecies were successfully isolated: B. garinii, B. burgdorferi sensu stricto, B. afzelii, B. valaisiana, and B. lusitaniae. Mixed infections were obtained from five of 140 infected ticks. The greatest diversity in Borrelia species was observed at the lowest altitude where all five Borrelia species were present, whereas at the two highest altitudes, B. lusitaniae was not observed.
  • Publication
    Accès libre
    Early detection of Borrelia burgdorferi sensu lato infection in Balb/c mice by co-feeding Ixodes ricinus ticks
    (2003)
    Hu, Chang Min
    ;
    Cheminade, Yves
    ;
    Perret, Jean-Luc
    ;
    Weynants, Vincent
    ;
    Lobet, Yves
    ;
    Gern, Lise 
    In Europe, Borrelia burgdorferi is transmitted by Ixodes ricinus to animals and human. When infected and uninfected ticks co-feed on a host, spirochetes are transmitted from ticks to animal and also to uninfected ticks. Here, we used uninfected ticks to co-feed with infected ticks on mice to evaluate this method to detect early infection in mice. A total of 128 mice were challenged by infected nymphs placed in capsules glued on the back of the mice. Three days later uninfected larvae were added in the capsule to co-feed with infected nymphs and were examined for Borrelia infection after natural detachment. Infection in mice was also determined by xenodiagnosis and by spirochete isolation from ear skin biopsy and back skin biopsy taken at the tick attachment site one month after infection. A total of 111 mice were found to be infected by at least one of these four methods. Borrelia infection was observed in 95% of mice by the co-feeding method, in 92% of mice by xenodiagnosis, in 69% and in 68% of mice by cultivation of ear and back skin biopsies, respectively. Our results demonstrate that the co-feeding method is a very sensitive method which can be used to detect very early infection in mice infected by tick bites.
  • Publication
    Accès libre
    Genetic diversity of Borrelia burgdorferi sensu lato isolates obtained from Ixodes ricinus ticks collected in Slovakia
    (1999)
    Gern, Lise 
    ;
    Hu, Chang Min
    ;
    Kocianova, Elena
    ;
    Vyrostekova, Vanda
    ;
    Rehacek, J.
    In Europe, Borrelia burgdorferi sensu lato is diverse, including B.burgdorferi s.s., B.garinii, B.afzelii, B.valaisiana and B.lusitaniae. In this study, we focused on the distribution of the different B.burgdorferi species among Ixodes ricinus adult ticks collected in an endemic area within Slovakia. We compared results of prevalence of B.burgdorferi infection in ticks obtained by immunofluorescence (IF) and by isolation. Isolates were characterized by restriction fragment length polymorphism (RFLP) of the rrf-rrl intergenic spacer genes using MseI. Using immunofluorescence we observed that 56/114 (49%) ticks were infected by B.burgdorferi s.l. Males were found to be more often infected (32/57, 56%) than females (24/57, 42%) but the difference was not significant (p=0.1895). From the same 114 ticks a total of 37 isolates were obtained: 19 from males (33%) and 18 from females (32%). The RFLP identification revealed 25 B.afzelii (68%), 5 B.garinii (14%), 5 B.valaisiana (14%) and 2 B.lusitaniae (5%). The infection in ticks was more often detected by IF than by isolation (p=0.0153) and isolation success was higher when the infection degree in ticks was high (p=0.0397). The infection prevalence observed in this area is among the highest observed in Europe.
  • Publication
    Accès libre
    Isolement d'un spirochète à partir d'Ixodes ricinus de Tunisie
    (1989)
    Zhioua, Elyes
    ;
    Gern, Lise 
    ;
    Aeschlimann, André 
    Un spirochète non identifié a été isolé à partir d’un exemplaire d’Ixodes ricinus, tique récoltée au « drapeau » dans la région d’Ain Draham, au nord-ouest de la Tunisie
  • Publication
    Accès libre
    Changes in the protein profile and antigenicity of different Borrelia burgdorferi strains after reintroduction to Ixodes ricinus ticks
    Min Hu, Chang
    ;
    Gern, Lise 
    ;
    Aeschlimann, André 
    Eight Swiss strains of Borrelia burgdorferi, with various protein profiles and the North-American strain B31 were artificially introduced into Ixodes ricinus ticks and reisolated 10 days later. All isolates were subsequently examined by SDS-PAGE analysis. Comparing initial isolates with the reisolates, we observed that 7 out of 9 strains changed their protein pattern with respect to the major proteins OspA, OspB and the 22 kDa protein after passage in the tick. The strains NE2, NE4 and NE83 with the initial phenotype of OspA and 22 kDa proteins changed to the phenotype of OspA and OspB, the strains B2 and NE202 with the initial phenotype of OspA acquired an additional protein of 22 kDa and the strain NE58 with the initial phenotype of OspA also acquired a protein of 22 kDa. Examination of these isolates by Western blot analysis demonstrated that the reaction with the monoclonal antibody H5332 and a monospecific polyclonal antibody PoAb/anti-22 kDa differed between the initial isolates and the reisolates.