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Gern, Lise

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Gern, Lise
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https://libra.unine.ch/handle/123456789/303

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  • 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
    Accès libre
    Influence of some climatic factors on Ixodes ricinus ticks studied along altitudinal gradients in two geographic regions in Switzerland
    (2008)
    Morán Cadenas, Francisca
    ;
    Burri, Caroline
    ;
    Gern, Lise 
    In the context of climate change, the seasonal activity of questing Ixodes ricinus and their infection with Borrelia burgdorferi sensu lato (s.l.) were examined in relation to some climatic data along altitudinal gradients in Switzerland. The first study took place in an Alpine area (Valais) from 750 to 1020 m above sea level. The other gradient was located on a mountain in the foothills of the Jura chain (Neuchâtel) from 620 to 1070 m above sea level. In the Alpine area, the highest questing tick density was observed at the highest altitude. At the lowest altitudes (750 and 880 m), very high saturation deficits, >10 mmHg, were present during most of the tick activity season and they seem to have impaired the thriving of tick populations. The second study in Neuchâtel (2003–2005) was a follow-up of a previous study (1999–2001) in which it was observed that tick density decreased with increasing altitude. During the follow-up study, substantial differences in questing tick density and phenology of ticks were observed: At high elevations, questing tick densities were 2.25 and 3.5 times higher for nymphs and adults, respectively, than during 1999–2001. As observed during 1999–2001, questing tick density decreased with increasing altitude in this site in 2003–2005. Tick questing density remained higher at the lowest altitude. Increased temperatures during summer months, more favorable for ticks, reaching values similar to those registered in the first study at the lowest elevations are probably responsible for the higher tick questing density at high altitudes. B. burgdorferi s.l. infection prevalence in ticks decreased with increasing altitudes along both altitudinal gradients. Long-lasting high saturation deficit values may limit the development of tick populations as too high a moisture stress has a negative effect on tick survival. This factor may have a permanent impact, as it is probably the case at the lowest altitudes in the Alpine area or a more transient effect like in the Neuchâtel gradient.
  • Publication
    Accès libre
    Assessment of intraspecific mtDNA variability of European Ixodes ricinus sensu stricto (Acari: Ixodidae)
    (Elsevier, 2008)
    Casati, Simona
    ;
    Bernasconi, Marco V.
    ;
    Gern, Lise 
    ;
    Jean-claude Piffaretti
    The Ixodes ricinus complex is composed of 14 species distributed worldwide. Some members of this complex are involved in the transmission of a number of diseases to animals and humans, in particular Lyme borreliosis, tick-borne encephalitis, ehrlichiosis and babesiosis. While the phylogenetic relationships between species of the I. ricinus complex have been investigated in the past, still little is known about the genetic structure within the species I. ricinus sensu stricto. We have investigated the intraspecific variability among 26 I. ricinus s.s. ticks collected in various European countries, including Switzerland, Italy, Austria, Denmark, Sweden, and Finland by using five mitochondrial gene fragments corresponding to the control region, 12S rDNA, cytb, COI, and COII. The five genes considered here showed a low genetic variability (1.6–5%). Our results based on both statistical parsimony (applied to the COI + COII + cytb + 12S + CR data set, for a total of 3423 bp) and maximum parsimony (applied to the COI + COII + cytb + 12S data set, for a total of 2980 bp) did not provide any evidence for a correlation between the identified haplotypes and their geographic origin. Thus, the European I. ricinus s.s. ticks do not seem to show any phylogeography structure.
  • Publication
    Accès libre
    Ixodes ticks belonging to the Ixodes ricinus complex encode a family of anticomplement proteins
    (2007)
    Daix, V.
    ;
    Schroeder, H.
    ;
    Praet, N.
    ;
    Georgin, J.-P.
    ;
    Chiappino, I.
    ;
    Gillet, L.
    ;
    de Fays, K.
    ;
    Decrem, Y.
    ;
    Leboulle, G.
    ;
    Godfroid, E.
    ;
    Bollen, A.
    ;
    Pastoret, P.-P.
    ;
    Gern, Lise 
    ;
    Sharp, P. M.
    ;
    Vanderplasschen, A.
    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
    Accès libre
    Diversity within Borrelia burgdorferi sensu lato genospecies in Switzerland by recA gene sequence
    (2004)
    Casati, Simona
    ;
    Bernasconi, Marco V.
    ;
    Gern, Lise 
    ;
    Piffaretti, Jean-Claude
    A total of 874 Ixodes ricinus ticks were collected in Switzerland to investigate the genetic diversity of the Borrelia population. We integrated to the RT-PCR method the DNA sequence analysis of a 162-bp fragment of the recA gene. Five genospecies were detected: Borrelia afzelii, Borrelia burgdorferi s.s., Borrelia garinii, Borrelia valaisiana, and Borrelia lusitaniae. A heterogeneous distribution was observed within the B. burgdorferi s.l. genospecies. The most prevalent and diverse genospecies found in Switzerland was Borrelia afzelii, which might suggest a rapid evolution of this genospecies.
  • Publication
    Accès libre
    Density of questing Ixodes ricinus nymphs and adults infected by Borrelia burgdorferi sensu lato in Switzerland: spatio-temporal pattern at a regional scale
    (2004)
    Jouda, Fatima
    ;
    Perret, Jean-Luc
    ;
    Gern, Lise 
    Lyme borreliosis, the most important vector-borne disease in the Northern hemisphere, causes health problem for populations in endemic areas. In the present study, the density of questing Ixodes ricinus ticks and their infection with Borrelia burgdorferi sensu lato (sl) was examined in 11 areas located on the Swiss Plateau and in an alpine valley. From 1999 to 2001, free-living I. ricinus ticks were collected on a monthly basis by flagging vegetation in these areas. Each tick was examined for the presence of B. burgdorferi sl using direct fluorescent antibody assay, and for isolation of the bacteria. Borreliae were characterized by PCR followed by RFLP. Density of questing ticks varied greatly between studied areas. Borreliae were observed in ticks collected in all investigated sites. However, the prevalence of infection differed significantly among areas. Infection prevalence varied from 9% to 40% in nymphs and from 22% to 47% in adults. Adult ticks were significantly more infected (129/366, 35%) than nymphs (109/552, 20%). There was no correlation between nymphal density and infection prevalence as well as between adult density and infection prevalence, but there was a correlation between density of ticks and density of infected ticks. During the spring peak of questing tick density, a range of 2-30.3 infected ticks per 100 m2 was observed. B. burgdorferi sl isolates (n = 129) were obtained from ticks collected in 10/11 areas. Five Borrelia species were identified: B. garinii, B. burgdorferi sensu stricto, B. afzelii, B. valaisiana, B. lusitaniae, and six mixed infections were also obtained. Borrelia species were heterogeneously distributed in the different areas.
  • Publication
    Accès libre
    Darkness induces mobility, and saturation deficit limits questing duration, in the tick Ixodes ricinus
    (2003)
    Perret, Jean-Luc
    ;
    Guerin, Patrick 
    ;
    Diehl, Peter-Allan 
    ;
    Vlimant, Michèle 
    ;
    Gern, Lise 
    The behaviour of Ixodes ricinus nymphs was recorded in 10-day experiments using computer-assisted video-tracking, in the absence of any host stimuli. These ticks switch spontaneously from questing in a desiccating atmosphere to quiescence in a water-saturated atmosphere after dark. Quantification of both questing and quiescence duration demonstrates that questing duration is inversely related to saturation deficit whereas quiescence duration is not. Distance walked after quiescence increased with desiccating conditions, while the distance walked after questing remained unchanged. Almost all locomotor activities of I. ricinus occurred during darkness under either a 14 h:10 h L:D or a 8 h:4 h L:D cycle. We established that all life stages of I. ricinus are equipped to sense shifts in light intensity with bilaterally placed strings of photoreceptors. This permits I. ricinus to use onset of darkness to trigger mobility when desiccation risk is reduced in nature.
  • Publication
    Accès libre
    Distribution and prevalence of Borrelia burgdorferi sensu lato in Ixodes ricinus ticks of canton Ticino (Switzerland)
    (2003)
    Jouda, Fatima
    ;
    Crippa, Mara
    ;
    Perret, Jean-Luc
    ;
    Gern, Lise 
    Free-living Ixodes ricinus ticks were collected from 12 different sites of canton Ticino, south of the Alps (Switzerland). Each tick was examined for the presence of Borrelia burgdorferi sensu lato (sl), the etiologic agent of Lyme borreliosis using direct fluorescent antibody assay, and isolation of the bacteria. Borreliae were characterized by PCR followed by RFLP. The abundance and infection rates of I. ricinus ticks varied greatly between the areas. Two localities were found free of Borrelia. The prevalence of infected ticks ranged from 5 to 19%. Most ticks (96%) were found infected by <50 spirochetes. Three B. burgdorferi sl species were successfully isolated: B. garinii dominated, followed by B. lusitaniae and B. valaisiana. Additionally, a mixed infection with B. garinii and B. valaisiana was observed. The distribution of the various Borrelia species in the different areas was heterogeneous. This is the first report of the presence of B. lusitaniae in I. ricinus in Switzerland.
  • Publication
    Accès libre
    Investigations on the Mode and Dynamics of Transmission and Infectivity of Borrelia burgdorferi Sensu Stricto and Borrelia afzelii in Ixodes ricinus Ticks
    (2002)
    Crippa, Mara
    ;
    Rais, Olivier 
    ;
    Gern, Lise 
    Borrelia burgdorferi sensu lato (sl), the agent of Lyme disease, is transmitted to the host during the blood meal of Ixodes ticks. In most unfed ticks, spirochetes are present in the midgut and migrate during blood feeding to the salivary glands, from which they are transmitted to the host via saliva. In the present study, the efficiency of Ixodes ricinus ticks to transmit B. afzelii and B. burgdorferi sensu stricto (ss) and their infectivity for mice were examined in relation to the duration of the blood meal. In addition, we investigated whether these two Borrelia species can penetrate intact skin. Three modes of infection of mice were studied: tick-bite infection, inoculation of tick homogenates, and transcutaneous infection by topical application of tick homogenates on mouse skin. Transmission of B. burgdorferi sl from I. ricinus nymphs to mouse increased with duration of tick attachment. B. afzelii-infected ticks start to transmit infection earlier (≤48 h) than B. burgdorferi ss-infected ticks. As previously shown for B. burgdorferi ss in Ixodes scapularis, B. burgdorferi ss and B. afzelii in unfed I. ricinus were noninfectious for mice when tick homogenates were inoculated. However, the inoculation of homogenates of ticks fed for 24 h readily produced infection in mice. Therefore, B. burgdorferi ss and B. afzelii spirochetes are potentially infectious in the tick before natural transmission can occur. None of the mice (n = 33) became infected by transcutaneous transmission when tick homogenates were applied on mouse skin, showing that B. burgdorferi ss and B. afzelii are unable to penetrate intact skin, in contrast to relapsing fever spirochetes. This study also shows that B. afzelii is transmitted by I. ricinus to the host earlier than B. burgdorferi ss and that I. ricinus seems to be a more efficient vector of B. afzelii than B. burgdorferi ss.
  • Publication
    Accès libre
    Relationship between Borrelia burgdorferi sensu lato species, red squirrels (Sciurus vulgaris) and Ixodes ricinus in enzootic areas in Switzerland
    (1998)
    Humair, Pierre-François
    ;
    Gern, Lise 
    The infection and reservoir status of red squirrels (Sciurus vulgaris) for Borrelia burgdorferi sensu lato were studied in Switzerland. B. burgdorferi sensu lato was isolated from 15 skin samples from 4/6 dead red squirrels, victims of road traffic. Isolates were identified using restriction fragment length polymorphism (RFLP): B. burgdorferi sensu stricto was present in 14 culture tubes containing skin samples and B. afzelii in two other tubes. A mixed infection was revealed in one case. A total of 227 ticks attached to squirrels were cultivated in BSKII medium and 90 isolates were obtained. Genotypic identification by RFLP showed that B. afzelii (59%) and B. burgdorferi sensu stricto (46%) dominated in ticks feeding on red squirrels. Data collected from one particular animal, highly infested with Ixodes ricinus and harbouring numerous Borrelia-infected Ixodes ricinus ticks, showed that transmission of B. burgdorferi sensu lato occurred from S. vulgaris to feeding ticks. More precisely, B. burgdorferi sensu stricto and B. afzelii were mainly transmitted from S. vulgaris to ticks. The present data emphasized the results obtained previously from small rodents and birds in Japan and in Switzerland, showing the occurrence of specific associations between host species and Borrelia genospecies.