Annexe 1

Principes des différentes méthodes d’échantillonnage des tiques Capture des tiques sur la végétation • Méthode du drapeau L’échantillonnage par la méthode du drapeau (dragging method) permet de prélever les tiques à l’affût en simulant le passage d’un hôte (MacLeod, 1932 ; Vassallo et al., 2000). Ce leurre mécanique est réalisé à partir d’une pièce de tissu, appelée drapeau, attachée à un bâton. Ce drapeau est traîné sur la végétation par le préleveur à l’aide d’une corde fixée aux deux extré..

A cautionary note on Bayesian estimation of population size by removal sampling with diffuse priors

International audienc

Bayesian estimation of abundance based on removal sampling under weak assumption of closed population with catchability depending on environmental conditions. Application to tick abundance

International audienceThe estimation of animal abundance is essential to understand population dynamics, species interactions and disease patterns in populations. Estimations of relative abundance classically are based on a single observation of several sites. In this case, the mapping of abundance assumes that the probability of detecting an individual, hence the sampling rate, remains constant across the observed sites. In practice, however, this assumption is often not satisfied as the sampling rate may fluctuate between sites due to random fluctuations and/or fluctuations associated with the sampling process, notably associated with the characteristics of the site. It is therefore important to account for variations in detection probability. Using a removal sampling design, we studied the performance of a Bayesian approach to estimate both sampling rates and abundance under the assumption of a closed population. The assumption of a closed population often is weakened when the number of successive samplings is large. The number of samplings has to be limited and optimal. We therefore examined the minimal number of successive samplings needed to achieve sufficient statistical accuracy while respecting underlying model assumptions. Using the same simulations, we also compared the performance of the Bayesian approach to the performance of the frequentist Hayne method based on linear regression. We show that the Bayesian approach proposed gives generally better estimations of population size than the Hayne method. The two methods give approximately the same results for the estimation of sampling rate. We then studied the variability of detection probability of Ixodes ricinus ticks sampled under several environmental conditions by using a hierarchical Bayesian model with a random effect. The estimated sampling rate varied between 33.9% and 47.4% for shrubs and 53.6% and 66.7% for dead leaves. The variability of the sampling rate due to the site decreased when the number of successive samplings considered in the model increased. The variability was lower in dead leaves than shrubs. This approach could be used routinely for ecological or epidemiological studies of ticks and species with comparable life histories

Au cœur de la séquence ERC – Tentatives de caractérisation de l’hétérogénéité des méthodes d’évaluation des impacts

National audienc

Blood-feeding behavior of <em>Aedes albopictus</em>, a vector of Chikungunya on La Réunion

International audienceChikungunya virus (CHIKV) has long been considered to be transmitted to humans by the human-biting mosquito Aedes aegypti, especially in Africa. However, the recent outbreak of CHIKV involved another vector, Aedes albopictus, and serological data in the literature suggest that several species of domestic or human-related vertebrates can be contaminated by this virus. However, the role of Ae. albopictus mosquitoes as potential enzootic vectors for CHIKV has not yet been evaluated. Here we investigate Ae. albopictus feeding and resting behaviors in an area where a CHIKV epidemic recently occurred, which means deciphering host-seeking and feeding behaviors on several vertebrate species, measuring endophagous/exophagous (activity), endophilic/exophilic (resting) behaviors and its diel (24 h, day/night) biting activity. Ae. albopictus was found to have bimodal daily feeding activities and was found to have exophagic (89%) and exophilic (87%) behaviors. Ae. albopictus showed an opportunistic feeding behavior on a wide range of hosts (from cold-blooded to warm-blooded animals), supporting that it can be implicated in various vertebrate-virus pathosystems. However, with equal availability of one of the four vertebrate hosts (calf, chicken, dog, and goat) proposed against human, Ae. albopictus significantly preferred human, supporting earlier data about its high degree of anthropophily. Multiple blood feeding was also reported in every combination (animal/human) offered to Ae. albopictus, enlightening the higher risks to spread an arbovirus to human population because of interrupted feeding. Such catholic behavior suggests that Ae. albopictus may act as a bridge vector for zoonotic viruses. Further epidemiological implications of this issue are discussed

Association of Virulence Genotype with Phylogenetic Background in Comparison to Different Seropathotypes of Shiga Toxin-Producing Escherichia coli Isolates

The distribution of virulent factors (VFs) in 287 Shiga toxin-producing Escherichia coli (STEC) strains that were classified according to Karmali et al. into five seropathotypes (M. A. Karmali, M. Mascarenhas, S. Shen, K. Ziebell, S. Johnson, R. Reid-Smith, J. Isaac-Renton, C. Clark, K. Rahn, and J. B. Kaper, J. Clin. Microbiol. 41:4930-4940, 2003) was investigated. The associations of VFs with phylogenetic background were assessed among the strains in comparison with the different seropathotypes. The phylogenetic analysis showed that STEC strains segregated mainly in phylogenetic group B1 (70%) and revealed the substantial prevalence (19%) of STEC belonging to phylogenetic group A (designated STEC-A). The presence of virulent clonal groups in seropathotypes that are associated with disease and their absence from seropathotypes that are not associated with disease support the concept of seropathotype classification. Although certain VFs (eae, stx(2-EDL933), stx(2-vha), and stx(2-vhb)) were concentrated in seropathotypes associated with disease, others (astA, HPI, stx(1c), and stx(2-NV206)) were concentrated in seropathotypes that are not associated with disease. Taken together with the observation that the STEC-A group was exclusively composed of strains lacking eae recovered from seropathotypes that are not associated with disease, the “atypical” virulence pattern suggests that STEC-A strains comprise a distinct category of STEC strains. A practical benefit of our phylogenetic analysis of STEC strains is that phylogenetic group A status appears to be highly predictive of “nonvirulent” seropathotypes

Les risques associés aux tiques dans les parcs urbains et périurbains lyonnais

National audienc

Ecological Factors Characterizing the Prevalence of Bacterial Tick-Borne Pathogens in Ixodes ricinus Ticks in Pastures and Woodlands ▿ §

Ecological changes are recognized as an important driver behind the emergence of infectious diseases. The prevalence of infection in ticks depends upon ecological factors that are rarely taken into account simultaneously. Our objective was to investigate the influences of forest fragmentation, vegetation, adult tick hosts, and habitat on the infection prevalence of three tick-borne bacteria, Borrelia burgdorferi sensu lato, Anaplasma phagocytophilum, and Rickettsia sp. of the spotted fever group, in questing Ixodes ricinus ticks, taking into account tick characteristics. Samples of questing nymphs and adults were taken from 61 pastures and neighboring woodlands in central France. The ticks were tested by PCR of pools of nymphs and individual adults. The individual infection prevalence was modeled using multivariate regression. The highest infection prevalences were found in adult females collected in woodland sites for B. burgdorferi sensu lato and A. phagocytophilum (16.1% and 10.7%, respectively) and in pasture sites for Rickettsia sp. (8.7%). The infection prevalence in nymphs was lower than 6%. B. burgdorferi sensu lato was more prevalent in woodlands than in pastures. Forest fragmentation favored B. burgdorferi sensu lato and A. phagocytophilum prevalence in woodlands, and in pastures, the B. burgdorferi sensu lato prevalence was favored by shrubby vegetation. Both results are probably because large amounts of edges or shrubs increase the abundance of small vertebrates as reservoir hosts. The Rickettsia sp. prevalence was maximal on pasture with medium forest fragmentation. Female ticks were more infected by B. burgdorferi sensu lato than males and nymphs in woodland sites, which suggests an interaction between the ticks and the bacteria. This study confirms the complexity of the tick-borne pathogen ecology. The findings support the importance of small vertebrates as reservoir hosts and make a case for further studies in Europe on the link between the composition of the reservoir host community and the infection prevalence in ticks

Intérêt des données de téléphonie mobile et des sciences participatives pour l’estimation et la compréhension du risque de transmission de maladies liées à l’environnement : Application aux maladies transmises par les tiques

National audienc

Age- and sex-dependent effects of long-term zinc supplementation on essential trace element status and lipid metabolism in European subjects:The Zenith Study

International audienceGiven the key role of Zn in many physiological functions, optimal Zn status could be a predictive parameter of successful ageing. However, the benefit of Zn supplementation is still a matter of debate since Zn supplementation has been reported to be associated with the alteration of Cu status and lipid metabolism. As part of the Zenith Project, the present study aimed to investigate, in free-living healthy European middle-aged and older subjects, the effect of Zn supplementation on the biochemical status of Zn, Fe and Cu and on lipid profile. Volunteers aged 55-70 (n 188) and 70-85 (n 199) years old participated in a double-blinded, randomised study and received a daily placebo, or Zn as 15 or 30 mg for 6 months. Zn supplementation did not significantly modify erythrocyte Zn levels or erythrocyte Cu,Zn-superoxide dismutase activity. But Zn supplementation at 15 or 30 mg/d for 6 months increased significantly serum Zn levels and Zn urinary excretion with no major adverse effects on Fe and Cu status or on lipid metabolism. However, Zn supplementation at 30 mg/d showed some age- and sex-dependent alterations in Fe status or lipid profile. Therefore, with respect to the key role of an optimal Zn status in successful ageing, Zn supplementation at 15 mg/d, when necessary, could be safely proposed regarding lipids and the risk of interaction with Fe and Cu