Ticks transmit more pathogens to humans and animals than any other arthropod. We describe the 2.1 Gbp nuclear genome of the tick, Ixodes scapularis (Say), which vectors pathogens that cause Lyme disease, human granulocytic anaplasmosis, babesiosis and other diseases. The large genome reflects accumulation of repetitive DNA, new lineages of retro-transposons, and gene architecture patterns resembling ancient metazoans rather than pancrustaceans. Annotation of scaffolds representing ∼57% of the genome, reveals 20,486 protein-coding genes and expansions of gene families associated with tick–host interactions. We report insights from genome analyses into parasitic processes unique to ticks, including host ‘questing', prolonged feeding, cuticle synthesis, blood meal concentration, novel methods of haemoglobin digestion, haem detoxification, vitellogenesis and prolonged off-host survival. We identify proteins associated with the agent of human granulocytic anaplasmosis, an emerging disease, and the encephalitis-causing Langat virus, and a population structure correlated to life-history traits and transmission of the Lyme disease agent.

In Europe, 6 of the 11 genospecies of Borrelia burgdorferi sensu lato are prevalent in questing Ixodes ricinus ticks. In most parts of Central Europe, B. afzelii, B. garinii, and B. valaisiana are the most frequent species, whereas B. burgdorferi sensu stricto, B. bissettii, and B. lusitaniae are rare. Previously, it has been shown that B. afzelii is associated with European rodents. Therefore, the aim of this study was to identify reservoir hosts of B. garinii and B. valaisiana in Slovakia. Songbirds were captured in a woodland near Bratislava and investigated for engorged ticks. Questing I. ricinus ticks were collected in the same region. Both tick pools were analyzed for spirochete infections by PCR, followed by DNA-DNA hybridization and, for a subsample, by nucleotide sequencing. Three of the 17 captured songbird species were infested with spirochete-infected ticks. Spirochetes in ticks that had fed on birds were genotyped as B. garinii and B. valaisiana, whereas questing ticks were infected with B. afzelii, B. garinii, and B. valaisiana. Furthermore, identical ospA alleles of B. garinii were found in ticks that had fed on the birds and in questing ticks. The data show that songbirds are reservoir hosts of B. garinii and B. valaisiana but not of B. afzelii. This and previous studies confirm that B. burgdorferi sensu lato is host associated and that this bacterial species complex contains different ecotypes.Lyme borreliosis is the most frequent arthropod-borne disease in humans living in moderate climates. Under the umbrella of the wider taxon Borrelia burgdorferi sensu lato, the bacteria constitute a group of 11 named genospecies, which were delineated based on DNA-DNA hybridization and sequence divergence of selected loci (2,32,34,39,40). In Europe, six genospecies are recorded as infecting Ixodes ricinus ticks (8,15,25), and the most prevalent genospecies are B. afzelii, B. garinii, and B. valaisiana (13, 25). In contrast to the case in northern America, B. burgdorferi sensu stricto and B. bissettii are relatively rare in Europe (8,13,15,25). B. lusitaniae seems to be restricted to the western Mediterranean Basin, where its infection prevalence in ticks has been reported to be very high locally (3).Since the delineation of genospecies in B. burgdorferi sensu lato, it has been discussed whether the species complex is differentiated ecologically (4,17,18,26,44 B. valaisiana (12, 17, 19, 27, 29). The transmission model also predicts that bird-and rodent-associated ecotypes of B. burgdorferi sensu lato segregate in individual questing ticks, a prediction that has also been validated (25).The present work was carried out in a region of Europe where B. afzelii, B. garinii, and B. valaisiana are prevalent in questing ticks. In a previous study carried out in the same region, we have demonstrated that rodents are the reservoir hosts of B. afzelii but not of B. garinii and B. valaisiana (13). For this reason, hosts other than rodents must contribute to the prevalence of B. garinii and B. valaisiana in questing tic...

Blackbirds (Turdus merula) and song thrushes (Turdus philomelos) were found to carry 95% of all spirocheteinfected tick larvae among 40 bird species captured in Central Europe. More than 90% of the infections were typed as Borrelia garinii and Borrelia valaisiana. We conclude that thrushes are key players in the maintenance of these spirochete species in this region of Central Europe.Lyme borreliosis is a tick-transmitted zoonosis caused by spirochete bacteria from the genus Borrelia. This genus comprises 13 named species, and at least 4 of these cause disease in humans, namely, Borrelia burgdorferi, Borrelia spielmanii, Borrelia afzelii, and Borrelia garinii (1,14). All known strains of Lyme borreliosis spirochetes are maintained in nature by vertebrate hosts and ixodid ticks, with humans being ecological dead-end hosts.For Europe, pheasants (Phasianus colchicus), a few seabird species, and some passerine bird species have been shown to be reservoir competent for B. garinii and B. valaisiana but not for B. afzelii, a rodent specialist (4,5,6,7,13). However, little is known about the roles of the numerous European woodland bird species in the ecology of Lyme borreliosis spirochetes (2, 13). Therefore, we captured birds of a wide range of species, many of which are migratory, and determined their importance as hosts to ticks and as reservoirs for Lyme borreliosis spirochetes in selected sites of Central Europe.Ticks were collected from birds captured in four woodlands in Slovakia (16) during 2001 and 2002 and, in 2003, at one woodland in the southeastern Czech Republic. Questing adult and nymphal Ixodes ricinus ticks were collected from Slovak sites. Extracted DNA (3) was subjected to nested PCR targeting the 5S-23S intergenic spacer and also, in some cases, the flaB gene of Lyme borreliosis spirochetes (8, 15). Spirochete infections determined in ticks were assigned to species by the reverse line blot assay (5,8,15) or by DNA sequencing.Risk factors for tick infestation and infection with B. burgdorferi genospecies were investigated in negative binomial and logistic regression models, respectively. Explanatory variables were month, year, site, and bird species. Data from the Czech Republic were excluded because of differences in collection year and bird species range. The level of significance was set at a P value of Ͻ0.05. Because of the poor fit of Poisson regression models, the negative binomial models were used. For detailed statistical methods and results, see the supplemental material.Tick infestations of birds. Of 529 birds captured (345 and 184 at sites in Slovakia and the Czech Republic, respectively, comprising 40 species of 17 families), 187 (145 in Slovakia and 42 in the Czech Republic) carried I. ricinus (463 and 157 larvae and 375 and 495 nymphs in Slovakia and the Czech Republic, respectively) (Table 1). In Slovakia, blackbirds (Turdus merula), song thrushes (Turdus philomelos), and European robins (Erithacus rubecula) carried 55.6% of all collected I. ricinus ticks. In the Czech Republic, Europea...