Gern, Lise

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.

2003, Sarih, M'Hammed, Jouda, Fatima, Gern, Lise, Postic, Danièle

To determine the infection rate of Ixodes ricinus (I. ricinus) ticks with Borrelia burgdorferi sensu lato (B. burgdorferi sl) and to assess the frequency of the individual Borrelia species in this tick species, a total of 295 I. ricinus were collected in Taza region (Northeast of Morocco), from January to June 2002. The presence of B. burgdorferi A was determined by direct fluorescence antibody assay (DFA) and by PCR after culture. B. burgdorferi sl isolates were identified at the species level by restriction fragment length polymorphism. analysis of amplified products. The mean rate of I. ricinus infection with B. burgdorferi sl was 47.8%. Isolation attempts in BSK II medium resulted in 26 pure isolates. However, PCR performed on culture medium allowed to identify 82 Borrelia DNAs. B. lusitaniae has been identified from 76 out of 82 infected I. ricinus ticks (92.7%). Three ticks were infected by B. burgdorferi ss, and three other ticks were infected by B. garinii. This is the first report of the presence of B. burgdorferi A in Morocco and more specifically of B. burgdorferi ss in North Africa.

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.

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.