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Gern, Lise

Nom
Gern, Lise
Affiliation principale
Fonction
Professeur associé
Email
lise.gern@unine.ch
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https://libra.unine.ch/handle/123456789/303

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  • Publication
    Métadonnées seulement
    Genetic variation in transmission success of the Lyme borreliosis pathogen Borrelia afzelii
    (2015)
    Tonetti, Nicolas 
    ;
    Voordouw, Maarten 
    ;
    Durand, Jonas 
    ;
    Monnier, Séverine
    ;
    Gern, Lise 
    The vector-to-host and host-to-vector transmission steps are the two critical events that define the life cycle of any vector-borne pathogen. We expect negative genetic correlations between these two transmission phenotypes, if parasite genotypes specialized at invading the vector are less effective at infecting the vertebrate host and vice versa. We used the tick-borne bacterium Borrelia afzelii, a causative agent of Lyme borreliosis in Europe, to test whether genetic trade-offs exist between tick-to-host, systemic (host-to-tick), and a third mode of co-feeding (tick-to-tick) transmission. We worked with six strains of B. afzelii that were differentiated according to their ospC gene. We compared the three components of transmission among the B. afzelii strains using laboratory rodents as the vertebrate host and a laboratory colony of Ixodes ricinus as the tick vector. We used next generation matrix models to combine these transmission components into a single estimate of the reproductive number (R0) for each B. afzelii strain. We also tested whether these strain-specific estimates of R0 were correlated with the strain-specific frequencies in the field. We found significant genetic variation in the three transmission components among the B. afzelii strains. This is the first study to document genetic variation in co-feeding transmission for any tick-borne pathogen. We found no evidence of trade-offs as the three pairwise correlations of the transmission rates were all positive. The R0 values from our laboratory study explained 45% of the variation in the frequencies of the B. afzelii ospC strains in the field. Our study suggests that laboratory estimates of pathogen fitness can predict the distribution of pathogen strains in nature.
  • 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.
  • 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
    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
    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
    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
    Métadonnées seulement
    Longitudinal study of Lyme borreliosis in a high risk population in Switzerland
    (1998)
    Zhioua, Elyes
    ;
    Gern, Lise 
    ;
    Aeschlimann, André 
    ;
    Sauvain, Marie-Josephe
    ;
    Van der Linden, Sjef
    ;
    Fahrer, Heinz
    Orienteers from all parts of Switzerland (n = 416) were included in a longitudinal study for lyme borreliosis. In spring 1986, the seroprevalence was 28.1 %. At the beginning of the study, 84.3 % of orienteers reported a history of tick bite, and 3.8 % reported a past history of lyme borreliosis. During the first (spring 1986-autumn 1986), second (autumn 1986-spring 1987) and third (spring 1987-autumn 1987) period, rates of seroconversion were 0.6 % 2.7 % and 2.1 % respectively. During the first and second period, clinical incidence were 1.0 % and 0.25 % respectively. No active lyme borreliosis was detected during the third period. Among orienteers who seroconverted during the study (n = 16), only two developed clinical symptoms. Hence, Borrelia burgdorferi infection is often asymptomatic.
  • Publication
    Métadonnées seulement
    Ixodes ticks belonging to the Ixodes ricinus complex encode a family of anticomplement proteins
    (2007)
    Daix, Virginie
    ;
    Schroeder, Hélène
    ;
    Praet, N
    ;
    Georgin, Jean-Pierre
    ;
    Chiappino, I
    ;
    Gillet, Laurent
    ;
    de Fays, Katalin
    ;
    Decrem, Yves
    ;
    Leboulle, Gérard
    ;
    Godfroid, Edmond
    ;
    Bollen, Alex
    ;
    Pastoret, Paul-Pierre
    ;
    Gern, Lise 
    ;
    Sharp, Paul
    ;
    Vanderplasschen, Alain
    The alternative pathway of complement is an important innate defence against pathogens including ticks. This component of the immune system has selected for pathogens that have evolved countermeasures. Recently, a salivary protein able to inhibit the alternative pathway was cloned from the American tick Ixodes scapularis (Valenzuela et al., 2000; J. Biol. Chem. 275, 18717-18723). Here, we isolated two different sequences, similar to Isac, from the transcriptome of I. ricinus salivary glands. Expression of these sequences revealed that they both encode secreted proteins able to inhibit the complement alternative pathway. These proteins, called I. ricinus anticomplement (IRAC) protein I and II, are coexpressed constitutively in I. ricinus salivary glands and are upregulated during blood feeding. Also, we demonstrated that they are the products of different genes and not of alleles of the same locus. Finally, phylogenetic analyses demonstrate that ticks belonging to the Ixodes ricinus complex encode a family of relatively small anticomplement molecules undergoing diversification by positive Darwinian selection.
  • Publication
    Métadonnées seulement
    Reservoir role of lizard Psammodromus algirus in transmission cycle of Borrelia burgdorferi sensu lato (Spirochaetaceae) in Tunisia
    (2006)
    Dsouli, Najla
    ;
    Younsi-Kabachii, Hend
    ;
    Postic, Danièle
    ;
    Nouira, Said
    ;
    Gern, Lise 
    ;
    Bouattour, Ali
    To investigate the reservoir role of the lizard Psammodromus algirus for the Lyme disease spirochete, 199 lizards were trapped from April to October 2003 in El Jouza, northwestern Tunisia. In this site, the infection rate of free-living Ixodes ricinus (L.) by Borrelia was evaluated by immunofluorescence as 34.6% for adult ticks and 12.5% for nymphs. Eighty percent of P. algirus (117/146) captured during this study were infested by I. ricinus, the predominant tick species collected from lizards. The intensity of tick infestation of this host by larvae and nymphs ranged from 0.14 to 7.07 and from 1.5 to 6.58, respectively. These immature stages of I. ricinus were found on lizards in spring and the beginning of summer, with a peak of intensity during June (10.16 immature ticks by lizard). Tissue cultures from lizards and xenodiagnosis with larval L ricinus were used to assess the infection and the ability, respectively, of infected lizards to transmit Borrelia to naive ticks. Seventeen percent of xenodiagnostic ticks (40/229) acquired B. lusitaniae while feeding on P. algirus. Therefore, we demonstrated the ability of the lizards to sustain Borrelia infection and to infect attached ticks, and we proved that P. algirus is a reservoir host competent to transmit B. lusitaniae.