Experimental in vitro transmission of Babesia sp. (EU1) by Ixodes ricinus

Babesia sp. (EU1), first characterized in 2003, has been implicated in human cases of babesiosis in Italy, Austria and Germany. It has been identified in roe deer and in its suspected tick vector, Ixodes ricinus, in several European countries. The aim of the present study was to validate the competence of I. ricinus as a vector of Babesia sp. (EU1) via experimental infections. For this purpose, a parasite strain isolated from roe deer was cloned in sheep erythrocytes. After experimental infections, parasite DNA was successfully amplified by PCR in both eggs and larvae originating from infected I. ricinus females and in the salivary glands of females exposed to Babesia sp. (EU1) as nymphs. We also demonstrate that infected females were able to transmit parasite DNA during a new blood meal. Together with previous epidemiological studies, these results validate I. ricinus as a competent vector for Babesia sp. (EU1)

Detection of Wolbachia in the Tick Ixodes ricinus is Due to the Presence of the Hymenoptera Endoparasitoid Ixodiphagus hookeri

The identification of micro-organisms carried by ticks is an important issue for human and animal health. In addition to their role as pathogen vectors, ticks are also the hosts for symbiotic bacteria whose impact on tick biology is poorly known. Among these, the bacterium Wolbachia pipientis has already been reported associated with Ixodes ricinus and other tick species. However, the origins of Wolbachia in ticks and their consequences on tick biology (known to be very diverse in invertebrates, ranging from nutritional symbionts in nematodes to reproductive manipulators in insects) are unknown. Here we report that the endoparasitoid wasp Ixodiphagus hookeri (Hymenoptera, Chalcidoidea, Encyrtidae) – strictly associated with ticks for their development - is infested at almost 100% prevalence by a W. pipientis strain belonging to a Wolbachia supergroup that has already been reported as associated with other hymenopteran parasitoids. In a natural population of I. ricinus that suffers high parasitism rates due to I. hookeri, we used specific PCR primers for both hymenopteran and W. pipientis gene fragments to show that all unfed tick nymphs parasitized by I. hookeri also harbored Wolbachia, while unparasitized ticks were Wolbachia-free. We demonstrated experimentally that unfed nymphs obtained from larvae exposed to I. hookeri while gorging on their vertebrate host also harbor Wolbachia. We hypothesize that previous studies that have reported W. pipientis in ticks are due to the cryptic presence of the endoparasitoid wasp I. hookeri. This association has remained hidden until now because parasitoids within ticks cannot be detected until engorgement of the nymphs brings the wasp eggs out of diapause. Finally, we discuss the consequences of this finding for our understanding of the tick microbiome, and their possible role in horizontal gene transfer among pathogenic and symbiotic bacteria

Apport de la génétique des populations pour déterminer le rôle respectif des mammifères et des oiseaux dans la dispersion passive de la tique Ixodes ricinus

National audienc

Whole body transcriptomes and new insights into the biology of the tick Ixodes ricinus

Background: Ixodes ricinus is the most important vector of tick-borne diseases in Europe. A better knowledge of its genome and transcriptome is important for developing control strategies. Previous transcriptomic studies of I. ricinus have focused on gene expression during the blood meal in specific tissues. To obtain a broader picture of changes in gene expression during the blood meal, our study analysed the transcriptome at the level of the whole body for both nymphal and adult ticks. Ixodes ricinus ticks from a highly inbred colony at the University of Neuchatel were used. We also analysed previously published RNAseq studies to compare the genetic variation between three wild strains and three laboratory strains, including the strain from Neuchatel. Results: RNA was extracted from whole tick bodies and the cDNA was sequenced, producing 162,872,698 paired-end reads. Our reference transcriptome contained 179,316 contigs, of which 31% were annotated using Trinotate. Gene expression was compared between ticks that differed by feeding status (unfed vs partially fed). We found that blood-feeding in nymphs and female adult ticks increased the expression of cuticle-associated genes. Using a set of 3866 single nucleotide polymorphisms to calculate the heterozygosity, we found that the wild tick populations of I. ricinus had much higher levels of heterozygosity than the three laboratory populations. Conclusion: Using high throughput strand-oriented sequencing for whole ticks in different stages and feeding conditions, we obtained a de novo assembly that significantly increased the genomic resources available for I. ricinus. Our study illustrates the importance of analysing the transcriptome at the level of the whole body to gain additional insights into how gene expression changes over the life-cycle of an organism. Our comparison of several RNAseq datasets shows the power of transcriptomic data to accurately characterize genetic polymorphism and for comparing different populations or sources of sequencing material

List of studies reporting the presence of <i>Wolbachia pipientis</i> associated with ticks.

<p>List of studies reporting the presence of <i>Wolbachia pipientis</i> associated with ticks.</p

<i>Ixodiphagus hookeri</i> (Hymenoptera : Chalcidoidea, Encyrtidae).

<p>A Female habitus. B Female ovipositing in an engorged nymphs of <i>Ixodes ricinus</i> (ovipositor indicated by the arrow). C Adults of <i>I. hookeri</i> around the dead body of an engorged nymph of <i>I. ricinus</i>. D Emergence hole from which parasitoids exit the dead body of the engorged nymph.</p

Phylogenetic tree of <i>Wolbachia pipientis</i>.

<p>A Neighbor-Joining tree based on the the <i>Ftsz</i> sequence obtained with MEGA5 using the Maximum Composite Likelihood distance. Only bootstrap values greater than 80% are shown. Letters A to F (at the right of the name of the host from which the <i>Wolbachia</i> was sequenced and of its accession number) refer to the <i>Wolbachia</i> supergroups already described <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0030692#pone.0030692-Casiraghi1" target="_blank">[58]</a>.</p

Parasitism rates of <i>Ixodes rcinus</i> due to <i>Ixodiphagus hookeri</i> and presence of <i>Wolbachia</i> in the wasps

<p>Parasitism rates of <i>Ixodes rcinus</i> due to <i>Ixodiphagus hookeri</i> and presence of <i>Wolbachia</i> in the wasps</p

Clinical and biological characterization of patients with low (0.1-2%) JAK2V617F allele burden at diagnosis

International audience.