The Biological and Ecological Features of Northbound Migratory Birds, Ticks, and Tick-Borne Microorganisms in the African-Western Palearctic

Identifying the species that act as hosts, vectors, and vehicles of vector-borne pathogens is vital for revealing the transmission cycles, dispersal mechanisms, and establishment of vector-borne pathogens in nature. Ticks are common vectors for pathogens causing human and animal diseases, and they transmit a greater variety of pathogenic agents than any other arthropod vector group. Ticks depend on the movements by their vertebrate hosts for their dispersal, and tick species with long feeding periods are more likely to be transported over long distances. Wild birds are commonly parasitized by ticks, and their migration patterns enable the long-distance range expansion of ticks. The African-Palearctic migration system is one of the world's largest migrations systems. African-Western Palearctic birds create natural links between the African, European, and Asian continents when they migrate biannually between breeding grounds in the Palearctic and wintering grounds in Africa and thereby connect different biomes. Climate is an important geographical determinant of ticks, and with global warming, the distribution range and abundance of ticks in the Western Palearctic may increase. The introduction of exotic ticks and their microorganisms into the Western Palearctic via avian vehicles might therefore pose a greater risk for the public and animal health in the future.

First molecular detection of Francisella-like endosymbionts in Hyalomma and Rhipicephalus tick species collected from vertebrate hosts from Sardinia island, Italy

Ticks are vectors of a wide variety of human and animal pathogens as well as non-pathogenic microorganisms acting as endosymbionts and whose role in ticks is still little known. Symbionts such as Francisella-like endosymbionts (FLEs) are members of Francisellaceae family with unknown pathogenicity, detected in both hard and soft ticks. A total of 236 ticks collected from several sites in Sardinia were screened for Francisella species by PCR using primers targeting a fragment of the 16S rRNA gene. DNA of Francisella was detected in 5.1% (12/236) of the ticks tested. Sequencing results revealed that seven Rhipicephalus sanguineus s.l., three Hyalomma marginatum, one Hy. lusitanicum, and one Rh. bursa ticks exhibited DNA with 99-100% similarity to Francisella-like endosymbionts isolated from different tick species all over the world. Further research is needed in order to better characterize FLE strains obtained in Sardinia and to better understand if their presence could be related to the infection with other zoonotic pathogens.

Range-wide genetic analysis of Dermacentor variabilis and its Francisella-like endosymbionts demonstrates phylogeographic concordance between both taxa

BACKGROUND

The American dog tick, Dermacentor variabilis, is an important vector of pathogens to humans, wildlife and domestic animals in North America. Although this tick species is widely distributed in the USA and Canada, knowledge of its range-wide phylogeographic patterns remains incomplete.

METHODS

We carried out a phylogenetic analysis of D. variabilis using samples collected from 26 USA states and five Canadian provinces. Tick samples (n = 1053 in total) originated from two main sources: existing archives (2000-2011), and new collections made from 2012 to 2013. We sequenced a 691 bp fragment of the cox1 gene from a subset (n = 332) of geographically diverse D. variabilis. DNA extracted from individual ticks (n = 1053) was also screened for a Francisella-like endosymbiont, using a targeted 16S rRNA sequencing approach, and important pathogens (Rickettsia spp. and Coxiella burnetii), using species-specific quantitative PCR assays.

RESULTS

Maximum parsimony analysis of cox1 sequences revealed two major groups within D. variabilis with distinct geographical distributions: one from the eastern USA/Canada (Group 1) and one from the west coast states of the USA (California and Washington; Group 2). However, genetic subdivisions within both of these two major groups were weak to moderate and not tightly correlated with geography. We found molecular signatures consistent with Francisella-like endosymbionts in 257 of the DNA extracts from the 1053 individual ticks, as well as Rickettsia spp. and Coxiella burnetii in a small number of ticks (n = 29 and 2, respectively). Phylogenetic patterns for Francisella-like endosymbionts, constructed using sequence data from the bacterial 16S rRNA locus, were similar to those for D. variabilis, with two major groups that had a nearly perfect one-to-one correlation with the two major groups within D. variabilis.

CONCLUSIONS

Our findings reveal a distinct phylogenetic split between the two major D. variabilis populations. However, high levels of genetic mixture among widely separated geographical localities occur within each of these two major groups. Furthermore, our phylogenetic analyses provide evidence of long-term tick-symbiont co-evolution. This work has implications for understanding the dispersal and evolutionary ecology of D. variabilis and associated vector-borne diseases.

Francisella species in ticks and animals, Iberian Peninsula

The presence of Francisella species in 2134 ticks, 93 lagomorphs and 280 small mammals from the Iberian Peninsula was studied. Overall, 19 ticks and 6 lagomorphs were positive for Francisella tularensis subsp. holarctica, suggesting, as described for other regions, that lagomorphs may have an important role in the maintenance of F. tularensis in nature. Of the 6 positive lagomorphs, 4 were identified as the European rabbit, Oryctogalus cuniculus. Additionally, 353 ticks and 3 small mammals were PCR positive for Francisella-like endosymbionts (FLEs) and one small mammal was also positive for Francisella hispaniensis-like DNA sequences. Among FLE positive specimens, a variety of sequence types were detected: ticks were associated with 5 lpnA sequence types, with only one type identified per tick, in contrast to 2 lpnA sequence types detected in a single wood mouse (Apodemus sylvaticus). To our knowledge, this is the first report of FLEs in free-living small mammals as well as the first detection of F. hispaniensis-like sequences in a natural setting.

Occurrence of Francisella spp. in Dermacentor reticulatus and Ixodes ricinus ticks collected in eastern Poland

A total of 530 questing Dermacentor reticulatus ticks and 861 questing Ixodes ricinus ticks were collected from Lublin province (eastern Poland) and examined for the presence of Francisella by PCR for 16S rRNA (rrs) and tul4 genes. Only one female D. reticulatus tick out of 530 examined (0.2%) was infected with Francisella tularensis subspecies holarctica, as determined by PCR of the rrs gene. None of 861 I. ricinus ticks were infected with F. tularensis. In contrast, the presence of Francisella-like endosymbionts (FLEs) was detected in more than half of the D. reticulatus ticks (50.4%) and 0.8% of the I. ricinus ticks. The nucleotide sequences of the FLEs detected in D. reticulatus exhibited 100% homology with the nucleotide sequence of the FLE strain FDrH detected in Hungary in D. reticulatus. In conclusion, our results suggest a low contribution of D. reticulatus and I. ricinus ticks to the circulation of F. tularensis in eastern Poland. This finding, however, needs to be confirmed by further studies in other areas. Our study confirmed the common infection of D. reticulatus with Francisella-like endosymbionts (FLEs) of unknown pathogenic potential and revealed, for the first time, a low grade of infection of I. ricinus with FLEs.