Gern, Lise

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.

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.

2007, Humair, Pierre-François, Douet, Véronique, Cadenas, Francisca Moran, Schouls, Leo M, Van de Pol, Ingrid, Gern, Lise

We developed an efficient molecular method for the identification of the bloodmeal sources in the tick Ixodes ricinus (L.), the European vector of the agents of Lyme borreliosis and tick-borne encephalitis. A approximate to 145-bp orthologous fragment of the vertebrate mitochondrial 12S rDNA was used as a molecular marker to discriminate host vertebrate species. The method consists of a single run polymerase chain reaction amplification of the 12S rDNA molecular marker by using nondegenerate primers followed by a reverse line blot hybridization assay by using specific oligonucleotide probes. The palette of probes allowed us to distinguish major groups of host vertebrates (e.g., mammals, small rodents, artiodactyls, birds, lizards) and to identify the bloodmeal sources at the genus or species level. External primers were designed and used to sequence the 12S rDNA molecular marker of a broad range of known or potential host vertebrate species (n = 60), including mammal (n = 28), bird (n = 31), and reptile (n = 1) species. The use of this technique coupled with known methods for identification of tick-borne pathogens (e.g., Borrelia burgdorferi sensu lato) allowed us to determine the source of infective bloodmeal and to identify reservoir species. The present method was successfully used to identify the source of bloodmeals in all feeding I. ricinus ticks and in half of questing field-collected L ricinus ticks. Moreover, the bloodmeal source was identified in 65% of ticks infected with B. burgdorferi sensu lato. Further development of this technique may be envisaged for the detection of other vector-borne patbogens and their reservoir hosts.

2004, Perret, Jean-Luc, Rais, Olivier, Gern, Lise

We studied the relationship between climate and Ixodes ricinus L. tick behavior by following every day the proportion of ticks questing in a tick population placed in polyamide mesh-delimited arenas in the field. Simultaneously, the phenology of the questing density of nymphs and adults was studied by sampling ticks in a close location. At any time during the year, the proportion of questing adults was significantly higher (mean 24%) than the proportion of questing nymphs (mean 12%). The proportion of questing nymphs and adults decreased stepwise with time. The proportion of. questing adults partially recovered after each decrease. In contrast, the proportion of questing nymphs was strongly reduced during a single short period in June and did not recover even partially. Decrease in the proportion of questing ticks was strongly related either to a peak in saturation deficit or to a drop in maximal relative humidity. No increase in the proportion of questing nymphs was observed in the arenas during autumn, although an autumn peak of nymphs was observed at the sampling location close to the arenas. This suggests that the autumn peak of nymphs observed in nature was due to newly emerged spring-fed larvae and not to reactivated spring active nymphs.

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.

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.

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.

2008, Gern, Lise

In Europe, Borrelia burgdorferi sensu late (sl) the agent of Lyme borreliosis circulates in endemic areas between Ixodes ricinus ticks and a large number of vertebrate hosts upon which ticks feed. Currently, at least 12 different Borrelia species belonging to the complex B. burgdorferi sl have been identified among which seven have been defected in 1. ricinus: B. burgdorferi sensu stricto (ss), B. garinii, B. afzelii, B. valaisiana, B. spielmanii and B. bisseffii. A few dozens of vertebrate hosts have been identified as reservoirs for these Borrelia species. Specific associations were rather early observed between hosts, ticks and borrelia species, like for example between rodents and B. afzelii and B. burgdorferi ss, and between birds and B. garinii and B. valaisiana. The complement present in the blood of the hosts is the active component in the Borrelia host specificity. Recent studies confirmed trends toward specific association between Borrelia, species and particular host, but also suggested that loose associations may be more frequent in transmission cycles in nature than previously thought.

2007, Cadenas, Francisca Moran, Schneider, Helene, Lommano, Elena, Burri, Caroline, Moret, Jacqueline, Gern, Lise

We tested two approaches to extract Borrelia DNA from live Ixodes ricinus ticks before polymerase chain reaction (PCR) and reverse line blotting (RLB): DNA extraction of one half of the tick after incubation in BSK medium and DNA extraction of the other half of the tick directly, using ammonium hydroxide. Among 2079 ticks, 31.2% (n = 649) were found to be Borrelia-infected by PCR-RLB test using at least one of the DNA extraction methods. Five hundred four ticks (24.2%) were found infected after incubation in BSK and 481 (23.1%) after direct DNA extraction from the tick. The difference was not significant. However, these prevalences were significantly lower when only one method was applied (23.1% and 24.2%) compared to the prevalence obtained by the use of both methods (31.2%). In 313 infected ticks discordant results were obtained, i.e., one half of the tick was found to be infected whereas the other half was uninfected. Among these ticks, B. garinii and B. burgdorferi sensu stricto (ss) were significantly more frequently identified in the half tick incubated in BSK. No significant differences were observed for B. burgdorferi ss, B. valaisiana, and for undetermined Borrelia species.

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 in above sea level) on the slope of a mountain in Chaumont (Neuchatel, 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, vas 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 : B. garinii, B. burgdorferi sensu stricto, B. afzelii, B. valaisiana, and B. lusitaniae. Mixed isolate 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.