A Novel Francisella-Like Endosymbiont in Haemaphysalis longicornis and Hyalomma asiaticum, China

Recent Progress on Tick-Borne Animal Diseases of Veterinary and Public Health Significance in China

Ticks and tick-borne diseases pose a growing threat to human and animal health, which has brought great losses to livestock production. With the continuous expansion of human activities and the development of natural resources, there are more and more opportunities for humans to contract ticks and tick-borne pathogens. Therefore, research on ticks and tick-borne diseases is of great significance. This paper reviews recent progress on tick-borne bacterial diseases, viral diseases, and parasitic diseases in China, which provides a theoretical foundation for the research of tick-borne diseases.

Prediction and validation of cross-protective candidate antigen of Hyalomma asiaticum cathepsin L between H. asiaticum and H. anatolicum

Hyalomma asiaticum and H. anatolicum are tick species in Eurasia and Africa with major medical and veterinary significance. Beside their direct pathogenic effects, H. asiaticum and H. anatolicum are vectors of important diseases of livestock and in some instances of zoonoses. In search of ways to address the increasing incidence of global acaricide resistance, tick control through vaccination is regarded as a sustainable alternative approach. Cathepsin L-like cysteine protease (CPL) is a potent hemoglobinase, and plays important roles in the digestion of blood acquired from a host. CPL from H. anatolicum (HanCPL) with high similarity (> 90%) for H. asiaticum CPL (HasCPL) were aligned by in silico analysis. After further in vitro validation, the anti-HasCPL sera have cross-reactivity between the different total native protein of life stages and tissues for H. asiaticum and H. anatolicum. Furthermore, we further confirmed that recombinant HasCPL (rHasCPL) immunized rabbits were partially cross-protected (54.8%) by H. anatolicum infestation.

Detection and Genotyping of Francisella tularensis in Animal Hosts and Vectors from Six Different Natural Landscape Areas, Gansu Province, China

Objective

Tularemia, also known as hare fever, is caused by the bacterium Francisella tularensis (F. tularensis) transmitted through diseased wild animals, blood sucking insects, or contaminated water or food, which is distributed worldwide. The purpose of this study was to investigate F. tularensis infection in animal hosts and vectors from six different natural landscape areas in Gansu Province and to identify the genotypes of the detected F. tularensis.

Methods

Rodents were captured by snap traps, and ticks were collected by dragging a cloth over the vegetation or from domestic animals. After species identification, DNA was isolated from the captured animals and detected by nested PCR assays targeting the F. tularensis fopA gene. The positive samples were further amplified to discriminate the species, and another two short-sequence tandem repeat regions (SSTR) were amplified to identify their genotypes. All positive fragments were sequenced and analyzed by ClustalX (5.0) and DNAClub software.

Results

A total of 407 rodents of 12 species were captured, among which six rodent species were positive for F. tularensis, with an overall prevalence of 3.93%. The geographical difference in infection rate was statistically significant. At the SSTR9 locus, there were 7 genotypes among positive rodent samples. A total of 1864 ticks were tested for evidence of tularemia by nested PCR assays, 69 of which were positive, with an average positive rate of 3.70% for F. tularensis in ticks. The positive rates were significantly different among different regions. Seven genotypes were identified at the SSTR9 locus, one of which seemed dominant in positive tick samples. All positive samples had the same genotype at the SSTR16 locus.

Conclusion

There is natural infection of F. tularensis among animal vectors and hosts in Gansu Province, with diverse genotypes.

Grappling with the tick microbiome

Ixodes scapularis and Ixodes pacificus are the predominant vectors of multiple human pathogens, including Borrelia burgdorferi, one of the causative agents of Lyme disease in North America. Differences in the habitats and host preferences of these closely related tick species present an opportunity to examine key aspects of the tick microbiome. While advances in sequencing technologies have accelerated a descriptive understanding of the tick microbiome, molecular and mechanistic insights into the tick microbiome are only beginning to emerge. Progress is stymied by technical difficulties in manipulating the microbiome and by biological variables related to the life cycle of Ixodid ticks. This review highlights these challenges and examines avenues to understand the significance of the tick microbiome in tick biology.

Molecular Evidence of Bartonella melophagi in Ticks in Border Areas of Xinjiang, China

Bartonella are gram-negative intracellular bacteria; certain species of Bartonella can cause diseases in mammals and humans. Ticks play a major role in the transmission of Bartonella. Xinjiang is the largest province in China according to land area and has one-third of the tick species in China; the infection rate of Bartonella in ticks in the Xinjiang border areas has not been studied in detail. Therefore, this study investigated tick infections by Bartonella in Xinjiang border areas, and the purpose of the study was to fill in gaps in information regarding the genetic diversity of tick infections by Bartonella in Xinjiang. We tested 1,549 tick samples from domestic animals (sheep and cattle) for Bartonella using ribC-PCR. Positive samples from the ribC-PCR assay for Bartonella spp. were further subjected to PCR assays targeting the ITS, rpoB and gltA genes followed by phylogenetic analyses. Bartonella DNA was detected in 2.19% (34/1,549) of tick samples, and the ITS, rpoB and gltA genes of ribC gene-positive samples were amplified to identify nine samples of Bartonella melophagi. In this study, molecular analysis was used to assess the presence and genetic diversity of B. melophagi in ticks collected from sheep and cattle from Xinjiang, China. This study provides new information on the presence and identity of B. melophagi in ticks from sheep and cattle.

Microbial community of Hyalomma lusitanicum is dominated by Francisella-like endosymbiont

Exploring tick associations with complex microbial communities and single-microbial partners, especially intracellular symbionts, has become crucial to understand tick biology. Of particular interest are the underlying interactions with biological consequences i.e. tick fitness, vector competence. In this study, we first sequenced the 16S rRNA bacterial phylogenetic marker in adult male ticks of Hyalomma lusitanicum collected from 5 locations in the province of Cáceres to explore the composition of its microbial community. Overall, 16S rRNA sequencing results demonstrated that the microbial community of H. lusitanicum is mostly dominated by Francisella-like endosymbionts (FLEs) (ranging from 52% to 99% of relative abundance) suggesting it is a key taxon within the microbial community and likely a primary endosymbiont. However, further research is required to explore the mechanisms underlying the interaction between FLEs and H. lusitanicum.

Mechanisms Affecting the Acquisition, Persistence and Transmission of Francisella tularensis in Ticks

Over 600,000 vector-borne disease cases were reported in the United States (U.S.) in the past 13 years, of which more than three-quarters were tick-borne diseases. Although Lyme disease accounts for the majority of tick-borne disease cases in the U.S., tularemia cases have been increasing over the past decade, with >220 cases reported yearly. However, when comparing Borrelia burgdorferi (causative agent of Lyme disease) and Francisella tularensis (causative agent of tularemia), the low infectious dose (<10 bacteria), high morbidity and mortality rates, and potential transmission of tularemia by multiple tick vectors have raised national concerns about future tularemia outbreaks. Despite these concerns, little is known about how F. tularensis is acquired by, persists in, or is transmitted by ticks. Moreover, the role of one or more tick vectors in transmitting F. tularensis to humans remains a major question. Finally, virtually no studies have examined how F. tularensis adapts to life in the tick (vs. the mammalian host), how tick endosymbionts affect F. tularensis infections, or whether other factors (e.g., tick immunity) impact the ability of F. tularensis to infect ticks. This review will assess our current understanding of each of these issues and will offer a framework for future studies, which could help us better understand tularemia and other tick-borne diseases.

Ticks (Acari: Ixodidae) on birds migrating to the island of Ponza, Italy, and the tick-borne pathogens they carry

Seasonal migration of birds between breeding and wintering areas can facilitate the spread of tick species and tick-borne diseases. In this study, 151 birds representing 10 different bird species were captured on Ponza Island, an important migratory stopover off the western coast of Italy and screened for tick infestation. Ticks were collected and identified morphologically. Morphological identification was supported through sequencing a fragment of the 16S mitochondrial gene. In total, 16 captured birds carried ticks from four tick species: Hyalomma rufipes (n = 14), Amblyomma variegatum (n = 1), Amblyomma sp. (n = 1), and Ixodes ventalloi (n = 2). All specimens were either larvae (n = 2) or nymphs (n = 16). All ticks were investigated for tick-borne pathogens using published molecular methods. Rickettsia aeschlimannii was detected in six of the 14 collected H. rufipes ticks. Additionally, the singular A. variegatum nymph tested positive for R. africae. In all 14 H. rufipes specimens (2 larvae and 12 nymphs), Francisella-like endosymbionts were detected. Four H. rufipes ticks tested positive for Borrelia burgdorferi sensu lato in a screening PCR but did not produce sufficient amplicon amounts for species identification. All ticks tested negative for tick-borne encephalitis virus, Crimean-Congo hemorrhagic fever virus, Coxiella burnetii, Coxiella-like organisms, Babesia spp., and Theileria spp. This study confirms the role of migratory birds in the spread and establishment of both exotic tick species and tick-borne pathogens outside their endemic range.

Exploring the Diversity Within the Genus Francisella - An Integrated Pan-Genome and Genome-Mining Approach

Pan-genome analysis is a powerful method to explore genomic heterogeneity and diversity of bacterial species. Here we present a pan-genome analysis of the genus Francisella, comprising a dataset of 63 genomes and encompassing clinical as well as environmental isolates from distinct geographic locations. To determine the evolutionary relationship within the genus, we performed phylogenetic whole-genome studies utilizing the average nucleotide identity, average amino acid identity, core genes and non-recombinant loci markers. Based on the analyses, the phylogenetic trees obtained identified two distinct clades, A and B and a diverse cluster designated C. The sizes of the pan-, core-, cloud-, and shell-genomes of Francisella were estimated and compared to those of two other facultative intracellular pathogens, Legionella and Piscirickettsia. Francisella had the smallest core-genome, 692 genes, compared to 886 and 1,732 genes for Legionella and Piscirickettsia respectively, while the pan-genome of Legionella was more than twice the size of that of the other two genera. Also, the composition of the Francisella Type VI secretion system (T6SS) was analyzed. Distinct differences in the gene content of the T6SS were identified. In silico approaches performed to identify putative substrates of these systems revealed potential effectors targeting the cell wall, inner membrane, cellular nucleic acids as well as proteins, thus constituting attractive targets for site-directed mutagenesis. The comparative analysis performed here provides a comprehensive basis for the assessment of the phylogenomic relationship of members of the genus Francisella and for the identification of putative T6SS virulence traits.

Bacterial community profiling highlights complex diversity and novel organisms in wildlife ticks

Ticks Acari:Ixodida transmit a greater variety of pathogens than any other blood-feeding group of arthropods. While numerous microbes have been identified inhabiting Australian Ixodidae, some of which are related to globally important tick-borne pathogens, little is known about the bacterial communities within ticks collected from Australian wildlife. In this study, 1,019 ticks were identified on 221 hosts spanning 27 wildlife species. Next-generation sequencing was used to amplify the V1-2 hypervariable region of the bacterial 16S rRNA gene from 238 ticks; Amblyomma triguttatum (n = 6), Bothriocroton auruginans (n = 11), Bothriocroton concolor (n = 20), Haemaphysalis bancrofti (n = 10), Haemaphysalis bremneri (n = 4), Haemaphysalis humerosa (n = 13), Haemaphysalis longicornis (n = 4), Ixodes antechini (n = 29), Ixodes australiensis (n = 26), Ixodes fecialis (n = 13), Ixodes holocyclus (n = 37), Ixodes myrmecobii (n = 1), Ixodes ornithorhynchi (n = 10), Ixodes tasmani (n = 51) and Ixodes trichosuri (n = 3). After bioinformatic analyses, over 14 million assigned bacterial sequences revealed the presence of recently described bacteria 'Candidatus Borrelia tachyglossi', 'Candidatus Neoehrlichia australis', 'Candidatus Neoehrlichia arcana' and 'Candidatus Ehrlichia ornithorhynchi'. Furthermore, three novel Anaplasmataceae species were identified in the present study including; a Neoehrlichia sp. in I. australiensis and I. fecialis collected from quenda (Isoodon fusciventer) (Western Australia), an Anaplasma sp. from one B. concolor from echidna (Tachyglossus aculeatus) (New South Wales), and an Ehrlichia sp. from a single I. fecialis parasitising a quenda (WA). This study highlights the diversity of bacterial genera harboured within wildlife ticks, which may prove to be of medical and/or veterinary importance 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.