A Coxiella-like endosymbiont is a potential vitamin source for the Lone Star tick

Molecular prevalence of Coxiella like endosymbionts and the first record of Coxiella burnetii in hard ticks from Southern Thailand

Eight hard tick species were identified among a total of 466 samples collected from vegetation in southern Thailand: Dermacentor compactus (n = 150), D. steini (n = 100), D. auratus (n = 85), D. tricuspis (n = 41), Haemaphysalis hystricis (n = 69), H. semermis (n = 3), H. shimoga (n = 2) and Amblyomma testudinarium (n = 16). In 93 ticks from these 8 species, Coxiella bacteria were detected via 16 S rRNA, groEL (60-kDa chaperone heat shock protein B) and rpoB (β subunit of bacterial RNA polymerase) genes. Interestingly, Coxiella burnetii was detected for the first time in H. hystricis and D. steini in Songkhla Province. Coxiella-like endosymbionts (CLEs) were also found in 84 ticks from 7 species, namely, D. compactus, D. auratus, D. tricuspis, H. hystricis, H. semermis, H. shimoga and A. testudinarium. Among these, CLEs associated with D. compactus and H. semermis were reported for the first time in Thailand. Phylogenetic analysis and generation of a haplotype network clearly revealed 2 distinct groups of Coxiella bacteria, namely, C. burnetii and CLEs. The nucleotide alignment of Coxiella 16 S rRNA revealed differences in bases at 3 positions between C. burnetii and CLEs. Thus, these differences could be used as liable molecular markers for discriminating these 2 groups in hard ticks.

The Tick Microbiome: The "Other Bacterial Players" in Tick Biocontrol

Hard ticks (family Ixodidae) are one of the most predominant arthropod disease vectors worldwide, second only to mosquitoes. In addition to harboring animal and human pathogens, ticks are known to carry a microbial community constituted of non-pathogenic organisms, which includes maternally inherited intracellular endosymbionts and other environmentally acquired extracellular microorganisms. These microbial communities, which include bacteria, viruses, protozoans, and fungi-with often commensal, mutualistic, or parasitic associations with the tick-comprise the tick microbiome, bacteria being the most studied community. Many bacterial taxa frequently reported in ticks include soil, plant, and animal-associated microbes, suggesting many are environmentally acquired, including members with known entomopathogenic potential, such as Bacillus thuringiensis, Bacillus spp., and Pseudomonas spp. It has been reported that microbial community composition can impact pathogen persistence, dissemination, and fitness in ticks. In the United States, Ixodes scapularis (northeast) and I. pacificus (west) are the predominant vectors of Borrelia burgdorferi, the causal agent of Lyme disease. Amblyomma americanum is another important tick vector in the U.S. and is becoming an increasing concern as it is the leading cause of alpha-gal syndrome (AGS, or red meat allergy). This condition is caused by tick bites containing the galactose alpha 1,3 galactose (alpha-gal) epitope in their saliva. In this paper, we present a summary of the tick microbiome, including the endosymbiotic bacteria and the environmentally acquired (here referred to as the non-endosymbiotic community). We will focus on the non-endosymbiotic bacteria from Ixodes spp. and Amblyomma americanum and discuss their potential for novel biocontrol strategies.

The epidemiological and infectious characteristics of novel types of Coxiella burnetii co-infected with Coxiella-like microorganisms from Xuyi County, Jiangsu province, China

Coxiella burnetii (C. burnetii) is the causative agent of Q fever, a type of zoonoses withwidespread distribution. In 2019, a case of Q fever was diagnosed by metagenomic next-generation sequencing (mNGS) method in Xuyi County (Jiangsu province, China). The seroprevalence of previous fever patients and the molecular epidemiology of Coxiella in wild hedgehogs and harbouring ticks around the confirmed patient were detected to reveal the genetic characteristics and pathogenicity of the Coxiella strains. Four of the 90 serum samples (4.44%) were positive for specific C. burnetii IgM antibody, suggesting that local humans are at risk of Q fever. The positive rates of C. burnetii in hedgehogs and ticks were 21.9% (7/32) and 70.5% (122/173), respectively. At least 3 strains of Coxiella were found prevalent in the investigated area, including one new genotype of pathogenic C. burnetii (XYHT29) and two non-pathogenic Coxiella-like organisms (XYHT19 and XYHT3). XYHT29 carried by ticks and wild hedgehogs successfully infected mice, imposing a potential threat to local humans. XYHT19, a novel Coxiella-like microorganism, was first discovered in the world to co-infect with C. burnetii in Haemaphysalis flava. The study provided significant epidemic information that could be used for prevention and control strategies against Q fever for local public health departments and medical institutions.

Temporal dynamics of the Hyalomma marginatum-borne pathogens in southern France

Spatio-temporal scales have a clear influence on microbial community distribution and diversity and should thus be applied to study the dynamics of microorganisms. The invasive tick species Hyalomma marginatum has recently become established in southern France. It may carry pathogens of medical and veterinary interest including the Crimean-Congo haemorrhagic fever virus, Rickettsia aeschlimannii, Theileria equi and Anaplasma phagocytophilum. Pathogenic communities of H. marginatum have been identified and their spatial distribution characterized, but their temporal dynamics remain unknown. Hyalomma marginatum ticks were collected from hosts at monthly intervals from February to September 2022 in a site in southern France to study their presence and temporal dynamics. Of the 281 ticks analysed, we detected pathogens including R. aeschlimannii, Anaplasma spp. and T. equi with infection rates reaching 47.0%, 4.6% and 11.0%, respectively. A total of 14.6% of ticks were infected with at least Theileria or Anaplasma, with monthly fluctuations ranging from 2.9% to 28.6%. Strong temporal patterns were observed for each pathogen detected, particularly for R. aeschlimannii, whose infection rates increased dramatically at the beginning of summer, correlated with monthly mean temperatures at the site. Based on these results, we hypothesise that R. aeschlimannii may be a secondary symbiont of H. marginatum and could be involved in the stress response to temperature increase and mediate thermal tolerance of H. marginatum. Analysis of monthly and seasonal fluctuations in pathogens transmitted by H. marginatum led us to conclude that the risk of infection is low but persists throughout the period of H. marginatum activity, with a notable increase in summer.

Molecular and genotyping techniques in diagnosis of Coxiella burnetii: An overview

Although we live in the genomic era, the accessibility of the complete genome sequence of Coxiella burnetii, the etiological agent of Q fever, has increased knowledge in the field of genomic diversity of this agent However, it is still somewhat of a "question" microorganism. The epidemiology of Q fever is intricate due to its global distribution, repository and vector variety, as well as absence of surveys defining the dynamic interaction among these factors. Moreover, C. burnetii is a microbial agent that can be utilized as a bioterror weapon. Therefore, typing techniques used to recognize the strains can also be used to trace infections back to their source which is of great significance. In this paper, the latest and current typing techniques of C. burnetii spp. are reviewed illustrating their advantages and constraints. Recently developed multi locus VNTR analysis (MLVA) and single-nucleotide polymorphism (SNP) typing methods are promising in improving diagnostic capacity and enhancing the application of genotyping techniques for molecular epidemiologic surveys of the challenging pathogen. However, most of these studies did not differentiate between C. burnetii and Coxiella-like endosymbionts making it difficult to estimate the potential role that ticks play in the epidemiology of Q fever. Therefore, it is necessary to analyze the vector competence of different tick species to transmit C. burnetii. Knowledge of the vector and reservoir competence of ticks is important for taking adequate preventive measures to limit infection risks. The significant prevalence observed for the IS1111 gene underscores its substantial presence, while other genes display comparatively lower prevalence rates. Methodological variations, particularly between commercial and non-commercial kit-based methods, result in different prevalence outcomes. Variations in sample processing procedures also lead to significant differences in prevalence rates between mechanical and non-mechanical techniques.

Metagenome reveals the midgut microbial community of Haemaphysalis qinghaiensis ticks collected from yaks and Tibetan sheep

BACKGROUND

Haemaphysalis qinghaiensis is a tick species distributed only in China. Due to its ability to transmit a variety of pathogens, including species of the genera Anaplasma, Rickettsia, Babesia, and Theileria, it seriously endangers livestock husbandry. However, the microbial community of the midgut of H. qinghaiensis females collected from yaks and Tibetan sheep has not yet been characterized using metagenomic sequencing technology.

METHODS

Haemaphysalis qinghaiensis were collected from the skins of yaks and Tibetan sheep in Gansu Province, China. Genomic DNA was extracted from the midguts and midgut contents of fully engorged H. qinghaiensis females collected from the two hosts. Metagenomic sequencing technology was used to analyze the microbial community of the two groups.

RESULTS

Fifty-seven phyla, 483 genera, and 755 species were identified in the two groups of samples. The ticks from the two hosts harbored common and unique microorganisms. At the phylum level, the dominant common phyla were Proteobacteria, Firmicutes, and Mucoromycota. At the genus level, the dominant common genera were Anaplasma, Ehrlichia, and Pseudomonas. At the species level, bacteria including Anaplasma phagocytophilum, Ehrlichia minasensis, and Pseudomonas aeruginosa along with eukaryotes such as Synchytrium endobioticum and Rhizophagus irregularis, and viruses such as the orf virus, Alphadintovirus mayetiola, and Parasteatoda house spider adintovirus were detected in both groups. In addition, the midgut of H. qinghaiensis collected from yaks had unique microbial taxa including two phyla, eight genera, and 23 species. Unique microorganisms in the midgut of H. qinghaiensis collected from Tibetan sheep included two phyla, 14 genera, and 32 species. Kyoto Encyclopedia of Genes and Genomes enrichment analysis revealed that the functional genes of the microbiome of H. qinghaiensis were annotated to six pathways, and the metabolic pathways included 11 metabolic processes, in which the genes involved in carbohydrate metabolism were the most abundant, followed by the genes involved in lipid metabolism.

CONCLUSIONS

These findings indicate that most of the microbial species in the collected H. qinghaiensis ticks were the same in both hosts, but there were also slight differences. The analytical data from this study have enhanced our understanding of the midgut microbial composition of H. qinghaiensis collected from different hosts. The database of H. qinghaiensis microbe constructed from this study will lay the foundation for predicting tick-borne diseases. Furthermore, a comprehensive understanding of tick microbiomes will be useful for understanding vector competency and interactions with ticks and midgut microorganisms.

Nutritional symbiosis in ticks: singularities of the genus Ixodes

Symbiosis with intracellular bacteria is essential for the nutrition of ticks, particularly through the biosynthesis of B vitamins. Yet, ticks of the genus Ixodes, which include major vectors of human pathogens, lack the nutritional symbionts usually found in other tick genera. This paradox raises questions about the mechanisms that Ixodes ticks use to prevent nutritional deficiencies. Nonetheless, Ixodes ticks commonly harbor other symbionts belonging to the order Rickettsiales. Although these obligate intracellular bacteria are primarily known as human pathogens, Rickettsiales symbionts often dominate the Ixodes microbial community without causing diseases. They also significantly influence Ixodes physiology, synthesize key B vitamins, and are crucial for immatures. These findings underscore unique associations between Rickettsiales and Ixodes ticks distinct from other tick genera.

Endosymbiont-derived metabolites are essential for tick host reproductive fitness

Ticks, like other obligatory blood-feeding arthropods, rely on endosymbiotic bacteria to supplement their diet with B vitamins lacking in blood. It has been suggested that additional metabolites such as L-proline may be involved in this nutritional symbiosis, but this has yet to be tested. Here, we studied the metabolite-based interaction between the brown dog tick Rhipicephalus sanguineus (Acari: Ixodidae) and its Coxiella-like endosymbionts (CLE). We measured amino acid titers and tested the effect of B vitamins and L-proline supplementation on the fitness of CLE-suppressed female ticks, displaying low titers of CLE. We found higher titers of L-proline in the symbiont-hosting organs of unfed ticks and in engorged blood-fed whole ticks. Supplementation of B vitamins increased the hatching rate of CLE-suppressed ticks; this effect appears to be stronger when L-proline is added. Our results indicate that L-proline is produced by CLE, and we suggest that CLE is essential in states of high metabolic demand that affects tick reproductive fitness, such as oogenesis and embryonic development. These findings demonstrate the broader effect of nutritional symbionts on their hosts and may potentially contribute to the control of ticks and tick-borne diseases.

IMPORTANCE

Coxiella-like endosymbionts (CLE) are essential to the brown dog tick Rhipicephalus sanguineus for feeding and reproduction. This symbiosis is based on the supplementation of B vitamins lacking in the blood diet. The involvement of additional metabolites has been suggested, but no experimental evidence is available as yet to confirm a metabolic interaction. Here, we show that B vitamins and L-proline, both of which contribute to tick reproductive fitness, are produced by CLE. These findings demonstrate the importance of symbiont-derived metabolites for the host's persistence and shed light on the complex bacteria-host metabolic interaction, which can be channeled to manipulate and control tick populations.

Host-bacteria interactions: ecological and evolutionary insights from ancient, professional endosymbionts

Interactions between eukaryotic hosts and their bacterial symbionts drive key ecological and evolutionary processes, from regulating ecosystems to the evolution of complex molecular machines and processes. Over time, endosymbionts generally evolve reduced genomes, and their relationship with their host tends to stabilize. However, host-bacteria relationships may be heavily influenced by environmental changes. Here, we review these effects on one of the most ancient and diverse endosymbiotic groups, formed by-among others-Legionellales, Francisellaceae, and Piscirickettsiaceae. This group is referred to as Deep-branching Intracellular Gammaproteobacteria (DIG), whose last common ancestor presumably emerged about 2 Ga ago. We show that DIGs are globally distributed, but generally at very low abundance, and are mainly identified in aquatic biomes. Most DIGs harbour a type IVB secretion system, critical for host-adaptation, but its structure and composition vary. Finally, we review the different types of microbial interactions that can occur in diverse environments, with direct or indirect effects on DIG populations. The increased use of omics technologies on environmental samples will allow a better understanding of host-bacterial interactions and help unravel the definition of DIGs as a group from an ecological, molecular, and evolutionary perspective.

Composition of the Midgut Microbiota Structure of Haemaphysalis longicornis Tick Parasitizing Tiger and Deer

Haemaphysalis longicornis is a common tick species that carries several pathogens. There are few reports on the influence of different hosts on the structure of midgut microflora in H. longicornis. In this study, midgut contents of fully engorged female H. longicornis were collected from the surface of tiger (Panthera tigris) and deer (Dama dama). The bacterial genomic DNA of each sample was extracted, and the V3-V4 regions of the bacterial 16S rRNA were sequenced using the Illumina NovaSeq sequencing. The diversity of the bacterial community of the fully engorged female H. longicornis on the surface of tiger was higher than that of deer. In total, 8 phyla and 73 genera of bacteria annotations were detected in the two groups. At the phylum level, the bacterial phyla common to the two groups were Proteobacteria, Firmicutes, and Actinobacteriota. At the genus level, there were 20 common bacterial genera, among which the relative abundances of Coxiella, Morganella, Diplorickettsia, and Acinetobacter were high. The Morganella species was further identified to be Morganella morganii. The alpha diversity index indicated that the bacterial diversity of the tiger group was higher than that of the deer group. Bacteroidota, Patescibacteria, Desulfobacterota, Verrucomicrobiota, and Cyanobacteria were solely detected in the tiger group. A total of 52 bacterial genera were unique in the tiger group, while one bacterial genus was unique in the deer group. This study indicates that there are differences in the structure of the gut bacteria of the same tick species among different hosts. Further culture-based methods are needed to provide a more comprehensive understanding of the tick microbiota parasitizing different hosts.

Tick symbiosis

As obligate blood-feeders, ticks serve as vectors for a variety of pathogens that pose threats on both human and livestock health. The microbiota that ticks harbor play important roles in influencing tick nutrition, development, reproduction, and vector. These microbes also affect the capacity of ticks to transmit pathogens (vector competence). Therefore, comprehending the functions of tick microbiota will help in developing novel and effective tick control strategies. Here, we summarize the effects of main tick symbiotic bacteria on tick physiology and vector competency.

Investigation of tick-borne bacterial microorganisms in Haemaphysalis ticks from Hebei, Shandong, and Qinghai provinces, China

Tick-borne microorganisms in many tick species and many areas of China are still not thoroughly investigated. In this study, 224 ticks including two species (Haemaphysalis longicornis and Haemaphysalis qinghaiensis) were collected from four cities in Hebei, Shandong, and Qinghai provinces, China. Ticks were screened for the presence of tick-borne bacterial microorganisms including Rickettsia, Anaplasmataceae (Anaplasma, Ehrlichia, Neoehrlichia, etc.), Coxiella, Borrelia, and Bartonella. Two Anaplasma species (Anaplasma ovis and Anaplasma capra) were detected in H. longicornis from Xingtai City of Hebei Province, with a positive rate of 3 % and 8 %, respectively. A Coxiella species was detected in H. longicornis ticks from all three locations in Hebei and Shandong provinces, with the positive rate ranging from 30 to 75 %. All the 16S and rpoB sequences were very similar (99.77-100 % identity) to Coxiella endosymbiont of Haemaphysalis ticks. An Ehrlichia species was detected in H. qinghaiensis (6/66, 9 %) from Xining City, Qinghai Province. The 16S and groEL sequences had 100 % and 97.40-97.85 % nucleotide identities to "Candidatus Ehrlichia pampeana" strains, respectively, suggesting that it may be a variant of "Candidatus Ehrlichia pampeana". All the ticks were negative for Rickettsia, Borrelia, and Bartonella. Because all the ticks were removed from goats or humans and were partially or fully engorged, it is possible that the microorganisms were from the blood meal but not vectored by the ticks. Our results may provide some information on the diversity and distribution of tick-borne pathogens in China.

Molecular detection of Coxiella burnetii in ticks collected from Iran

The present study was conducted with the aim of investigating the prevalence and genetic structure of Coxiella burnetii in tick samples collected from domestic animals in Hormozgan province146 tick samples were randomly collected from cattle, sheep, goat, camel and dog herds in seven cities of Hormozgan. After the DNA was extracted from each tick sample; Nested-PCR method was used to identify the presence of C. burnetii using IS1111 transposon gene and isocitrate dehydrogenase icd gene. In addition, phylogenetic analysis and tree diagram were constructed based on IS1111 and icd genes. The results showed that out of 146 pool tick samples, 40 pool samples based on IS1111 gene and 32 pool samples based on icd gene were infected with C. burnetii. When results were stratified by livestock type, infection rates were highest in sheep ticks (37.5%, 95% CI: 21.2% - 57.29%), followed by cattle ticks (32.14%, 95% CI: 17.90% - 50.66%) and dog tick (15%, 95% CI: 70.6% - 29%). In camel and goat ticks, the infection rate was 15.90 and 23.07%, respectively. In conclusion, this study emphasizes the role of ticks as potential carriers of C. burneti. The results indicate the importance of cattle, sheep, goats, camels and dogs in Hormozgan region as effective factors in the epidemiology of Q fever and its impact on public health. In addition, a high degree of similarity (from 99% to 100%) was observed between IS1111 and icd genes in this study and recorded sequences from different regions of the world.

Microbiome of Invasive Tick Species Haemaphysalis longicornis in North Carolina, USA

Ticks are one of the most important vectors of human and animal disease worldwide. In addition to pathogens, ticks carry a diverse microbiota of symbiotic and commensal microorganisms. In this study, we used next-generation sequencing (NGS) to survey the microbiomes of Haemaphysalis longicornis (Acari: Ixodidae) at different life stages collected from field populations in North Carolina (NC), USA. Sequence analyses were performed using QIIME2 with the DADA2 plugin and taxonomic assignments using the Greengenes database. Following quality filtering and rarefaction, the bacterial DNA sequences were assigned to 4795 amplicon sequence variants (ASVs) in 105 ticks. A core microbiome of H. longicornis was conserved across all ticks analyzed, and included bacterial taxa: Coxiella, Sphingomonas, Staphylococcus, Acinetobacter, Pseudomonas, Sphingomonadaceae, Actinomycetales, and Sphingobium. Less abundant bacterial taxa, including Rickettsia and Aeromonas, were also identified in some ticks. We discovered some ASVs that are associated with human and animal infections among the identified bacteria. Alpha diversity metrics revealed significant differences in bacterial diversity between life stages. Beta diversity metrics also revealed that bacterial communities across the three life stages were significantly different, suggesting dramatic changes in the microbiome as ticks mature. Based on these results, additional investigation is necessary to determine the significance of the Haemaphysalis longicornis microbiome for animal and human health.

Tetracycline inhibits tick host reproduction by modulating bacterial microbiota, gene expression and metabolism levels

BACKGROUND

Ticks are disease vectors that are a matter of worldwide concern. Antibiotic treatments have been used to explore the interactions between ticks and their symbiotic microorganisms. In addition to altering the host microbial community, antibiotics can have toxic effects on the host.

RESULTS

In the tick Haemaphysalis longicornis, engorged females showed reproductive disruption after microinjection of tetracycline. Multi-omics approaches were implemented to unravel the mechanisms of tick reproductive inhibition in this study. There were no significant changes in bacterial density in the whole ticks on Day (D)2 or D4 after tetracycline treatment, whereas the bacterial microbial community was significantly altered, especially on D4. The relative abundances of the bacteria Staphylococcus, Bacillus and Pseudomonas decreased after tetracycline treatment, whereas the relative abundances of Coxiella and Rhodococcus increased. Ovarian transcriptional analysis revealed a cumulative effect of tetracycline treatment, as there was a significant increase in the number of differentially expressed genes with treatment time and a higher number of downregulated genes. The tick physiological pathways including lysosome, extracellular matrix (ECM)-receptor interaction, biosynthesis of ubiquinone and other terpenoids-quinones, insect hormone biosynthesis, and focal adhesion were significantly inhibited after 4 days of tetracycline treatment. Metabolite levels were altered after tetracycline treatment and the differences increased with treatment time. The differential metabolites were involved in a variety of physiological pathways; the downregulated metabolites were significantly enriched in the nicotinate and nicotinamide metabolism, galactose metabolism, and ether lipid metabolism pathways.

CONCLUSIONS

These findings indicate that tetracycline inhibits tick reproduction through the regulation of tick bacterial communities, gene expression and metabolic levels. The results may provide new strategies for tick control. © 2023 Society of Chemical Industry.

Revealing the Diversity of the Mycobiome in Different Phases of Ticks: ITS Gene-Based Analysis

Ticks are obligate ectoparasites and vectors of a variety of pathogens in humans and animals. Certain tick-borne pathogens (TBPs) have been identified as the cause of zoonoses, posing potentially significant threats to the human health and livestock industries. Fungi are one of the major TBPs that can affect ticks and cause disease in humans. At present, there are few studies on the diversity of fungal microbial communities carried by Ixodes. Therefore, profiling tick-borne fungi will contribute to understanding the tick-fungal interaction. This study evaluated the community profile and differences in the fungal microbiome in Ixodidae collected on parasitic ticks or nonparasitic ticks in Wuwei, Gansu Province, China. The Shannon index, Simpson index, and Richness index were used to evaluate the diversity of mycobiome. Principle coordinates analysis (PCoA) was conducted to determine patterns of diversity in mycobiome. Using correlation analysis to determine the correlation of mycobiome. The results show that the high-throughput sequencing of the internal transcribed spacer gene generated 3,634,943 raw reads and 7,482 amplicon sequence variants. The dominant tick species in this region was Dermacentor nuttalli (Ixodidae). The mycobiome belonged to four classes-Dothideomycetes, Sordariomycetes, Ustilaginomycetes, and Tremellomycetes-and more than 261 genera, the most abundant genera were Cladosporium, Purpureocillium, Aureobasidium, Tranzscheliella, and Sporormiella. Alpha diversity indicated that the abundance and evenness of mycobiome were marginally higher in nonparasitic ticks than in parasitic ticks. PCoA showed that the community structures of parasitic ticks vary from nonparasitic ticks, samples from nonparasitic ticks tended to cluster more closely than those from the parasitic ticks. Correlation analysis indicated that there was a significant positive correlation or negative correlation between the mycobiome. Our results indicate that the mycobiome carried by Dermacentor nuttalli had rich diversity, and there was a significant difference in mycobiome between parasitic ticks and nonparasitic ticks. These findings may conducive to understand the complex interaction between ticks and commensal fungi and provide help for the further exploration of the behavioral characteristics of ticks and formulation of effective biological control measures.

Assessing the Influence of Climate Change and Environmental Factors on the Top Tick-Borne Diseases in the United States: A Systematic Review

In the United States (US), tick-borne diseases (TBDs) have more than doubled in the past fifteen years and are a major contributor to the overall burden of vector-borne diseases. The most common TBDs in the US-Lyme disease, rickettsioses (including Rocky Mountain spotted fever), and anaplasmosis-have gradually shifted in recent years, resulting in increased morbidity and mortality. In this systematic review, we examined climate change and other environmental factors that have influenced the epidemiology of these TBDs in the US while highlighting the opportunities for a One Health approach to mitigating their impact. We searched Medline Plus, PUBMED, and Google Scholar for studies focused on these three TBDs in the US from January 2018 to August 2023. Data selection and extraction were completed using Covidence, and the risk of bias was assessed with the ROBINS-I tool. The review included 84 papers covering multiple states across the US. We found that climate, seasonality and temporality, and land use are important environmental factors that impact the epidemiology and patterns of TBDs. The emerging trends, influenced by environmental factors, emphasize the need for region-specific research to aid in the prediction and prevention of TBDs.

Analysis of the bacterial community in female Rhipicephalus microplus ticks from selected provinces in Luzon, Philippines, using next-generation sequencing

Analysis of the tick microbiome can help understand tick-symbiont interactions and identify undiscovered pathogens, which may aid in implementing control of ticks and tick-borne diseases. The tropical cattle tick Rhipicephalus microplus is a widespread ectoparasite of cattle in the Philippines, negatively affecting animal productivity and health. This study characterized the bacterial community of R. microplus from Luzon, Philippines, through next-generation sequencing of 16s rRNA. DNA was extracted from 45 partially engorged female ticks from nine provinces. The DNA samples were pooled per province and then sequenced and analyzed using an open-source bioinformatics platform. In total, 667 operational taxonomic units (OTUs) were identified. The ticks in all nine provinces were found to have Coxiella, Corynebacterium, Staphylococcus, and Acinetobacter. Basic local alignment search tool (BLAST) analysis revealed the presence of known pathogens of cattle, such as Bartonella, Ehrlichia minasensis, and Dermatophilus congolensis. The tick samples from Laguna, Quezon, and Batangas had the most diverse bacterial species, whereas the tick samples from Ilocos Norte had the lowest diversity. Similarities in the composition of the bacterial community in ticks from provinces near each other were also observed. This is the first study on metagenomic analysis of cattle ticks in the Philippines, providing new insights that may be useful for controlling ticks and tick-borne diseases.

Characterization of the bacterial microbiota of cattle ticks in northeastern Thailand through 16S rRNA amplicon sequencing

Ticks are vectors of a variety of pathogens that can infect humans and animals. Ticks also harbor non-pathogenic microbiota. This study characterized the microbiota of the ticks infesting beef cattle in Thailand. Two species of ticks; Rhipicephalus microplus (n = 15) and Haemaphysalis bispinosa (n = 5), were collected in seven provinces in northeastern Thailand. Microbial community profile of ticks was examined based on sequences of the V3-V4 region of 16S rRNA gene. Proteobacteria (Pseudomonadota) was the most abundant phylum, followed by Firmicutes (Bacillota), and Actinobacteriota. Coxiella-like endosymbiont was the most abundant bacterial taxon overall (49% of sequence reads), followed by Anaplasma (8.5%), Corynebacterium (5.5%), Ehrlichia (3.9%), and Castellaniella (3.4%). Co-infections of the pathogenic bacteria Ehrlichia and Anaplasma were detected in 19/20 (95%) female ticks. The tick with the lowest number of bacteria had the lowest abundance of the Coxiella-like endosymbiont, and the pathogenic bacteria Anaplasma and Ehrlichia were absent. This study provides baseline information of the microbiota of cattle ticks in northeastern Thailand, suggesting that ticks carry a few dominant bacterial taxa that are primarily non-pathogenic but can co-occur with pathogenic microorganisms. The information obtained is useful for monitoring disease outbreaks in the future and informing prevention and control strategies against cattle tick-borne diseases.

Microbiota in disease-transmitting vectors

Haematophagous arthropods, including mosquitoes, ticks, flies, triatomine bugs and lice (here referred to as vectors), are involved in the transmission of various pathogens to mammals on whom they blood feed. The diseases caused by these pathogens, collectively known as vector-borne diseases (VBDs), threaten the health of humans and animals. Although the vector arthropods differ in life histories, feeding behaviour as well as reproductive strategies, they all harbour symbiotic microorganisms, known as microbiota, on which they depend for completing essential aspects of their biology, such as development and reproduction. In this Review, we summarize the shared and unique key features of the symbiotic associations that have been characterized in the major vector taxa. We discuss the crosstalks between microbiota and their arthropod hosts that influence vector metabolism and immune responses relevant for pathogen transmission success, known as vector competence. Finally, we highlight how current knowledge on symbiotic associations is being explored to develop non-chemical-based alternative control methods that aim to reduce vector populations, or reduce vector competence. We conclude by highlighting the remaining knowledge gaps that stand to advance basic and translational aspects of vector-microbiota interactions.

Impact of endosymbionts on tick physiology and fitness

Ticks transmit pathogens and harbour non-pathogenic, vertically transmitted intracellular bacteria termed endosymbionts. Almost all ticks studied to date contain 1 or more of Coxiella, Francisella, Rickettsia or Candidatus Midichloria mitochondrii endosymbionts, indicative of their importance to tick physiology. Genomic and experimental data suggest that endosymbionts promote tick development and reproductive success. Here, we review the limited information currently available on the potential roles endosymbionts play in enhancing tick metabolism and fitness. Future studies that expand on these findings are needed to better understand endosymbionts’ contributions to tick biology. This knowledge could potentially be applied to design novel strategies that target endosymbiont function to control the spread of ticks and pathogens they vector.

Molecular detection of Coxiella spp. in ticks (Ixodidae and Argasidae) infesting domestic and wild animals: with notes on the epidemiology of tick-borne Coxiella burnetii in Asia

Tick-borne Coxiella spp. are emerging in novel regions infecting different hosts, but information regarding their occurrence is limited. The purpose of this study was the molecular screening of Coxiella spp. in various ticks infesting goats, sheep, camels, cattle, wild mice, and domestic fowls (Gallus gallus domesticus) in various districts of Khyber Pakhtunkhwa, Pakistan. Morphologically identified tick species were confirmed by obtaining their cox1 sequences and were molecularly screened for Coxiella spp. by sequencing GroEL fragments. Almost 345 out of 678 (50.9%) hosts were infested by nine tick species. Regarding the age groups, the hosts having an age >3 years were highly infested (192/345, 55.6%), while gender-wise infestation was higher in female hosts (237/345, 68.7%). In collected ticks, the nymphs were outnumbered (613/1,119, 54.8%), followed by adult females (293/1,119, 26.2%) and males (213/1,119, 19.7%). A total of 227 ticks were processed for molecular identification and detection of Coxiella spp. The obtained cox1 sequences of nine tick species such as Hyalomma dromedarii, Hyalomma anatolicum, Haemaphysalis cornupunctata, Haemaphysalis bispinosa, Haemaphysalis danieli, Haemaphysalis montgomeryi, Rhipicephalus haemaphysaloides, Rhipicephalus microplus, and Argas persicus showed maximum identities between 99.6% and 100% with the same species and in the phylogenetic tree, clustered to the corresponding species. All the tick species except Ha. danieli and R. microplus were found positive for Coxiella spp. (40/227, 17.6%), including Coxiella burnetii (15/40, 6.7%), Coxiella endosymbionts (14/40, 6.3%), and different Coxiella spp. (11/40, 4.9%). By the BLAST results, the GroEL fragments of Coxiella spp. showed maximum identity to C. burnetii, Coxiella endosymbionts, and Coxiella sp., and phylogenetically clustered to the corresponding species. This is the first comprehensive report regarding the genetic characterization of Coxiella spp. in Pakistan's ticks infesting domestic and wild hosts. Proper surveillance and management measures should be undertaken to avoid health risks.

Epidemiology of Zoonotic Coxiella burnetii in The Republic of Guinea

BACKGROUND

Q fever is a zoonotic infectious disease characterized by fever, malaise, chills, significant weakness, and muscle pain. In some cases, the disease can become chronic and affect the inner membranes of the heart, such as the valves, leading to endocarditis and a high risk of death. Coxiella burnetii (C. burnetii) is the primary causative agent of Q fever in humans. This study aims to monitor the presence of C. burnetii in ticks collected from small mammals and cattle in the Republic of Guinea (RG).

METHODS

Rodents were trapped in the Kindia region of RG during 2019-2020, and ticks were collected from cattle in six regions of RG. Total DNA was extracted using a commercial kit (RIBO-prep, InterLabService, Russia) following the manufacturer's instructions. Real-time PCR amplification was conducted using the kit (AmpliSens Coxiella burnetii-FL, InterLabService, Russia) to detect C. burnetii DNA.

RESULTS AND CONCLUSIONS

Bacterial DNA was detected in 11 out of 750 (1.4%) small mammals and 695 out of 9620 (7.2%) tick samples. The high number of infected ticks (7.2%) suggests that they are the main transmitters of C. burnetii in RG. The DNA was detected in the liver and spleen of a Guinea multimammate mouse, Mastomys erythroleucus. These findings demonstrate that C. burnetii is zoonotic in RG, and measures should be taken to monitor the bacteria's dynamics and tick prevalence in the rodent population.

Metagenomic profile of the bacterial communities associated with Ixodes granulatus (Acari: Ixodidae): a potential vector of tick-borne diseases

Ixodes granulatus Supino, 1897 (Acari: Ixodida) is one of Malaysia's most common hard ticks and is a potential vector for tick-borne diseases (TBDs). Despite its great public health importance, research on I. granulatus microbial communities remains largely unexplored. Therefore, this study aimed to investigate the bacterial communities of on-host I. granulatus collected from three different recreational areas on the East Coast of Peninsular Malaysia using high throughput Next Generation Sequencing (NGS). A total of 9 females on-host I. granulatus were subjected to metabarcoding analysis targeting V3-V4 regions of 16S ribosomal RNA (rRNA) using the Illumina MiSeq platform. This study identified 15 bacterial phyla corresponding to 19 classes, 54 orders, and 90 families from 435 amplicon sequence variants (ASVs), revealing a diverse bacterial community profile. Together with 130 genera assigned, local I. granulatus harbored 4 genera of pathogens, i.e., Rickettsia da Rocha Lima, 1916 (Rickettsiales: Rickettsiaceae) (58.6%), Borrelia Swellengrebel 1907 (Spirochaetales: Borreliaceae) (31.6%), Borreliella Adeolu and Gupta 2015 (Spirochaetales: Borreliaceae) (0.6%), and Ehrlichia Cowdria Moshkovski 1947 (Rickettsiales: Ehrlichiaceae) (39.9%). Some endosymbiont bacteria, such as Coxiella (Philip, 1943) (Legionellales: Coxiellaceae), Wolbachia Hertig 1936 (Rickettsiales: Ehrlichiaceae), and Rickettsiella Philip, 1956 (Legionellales: Coxiellaceae), were also detected at very low abundance. Interestingly, this study reported the co-infection of Borrelia and Ehrlichia for the first time, instilling potential health concerns in the context of co-transmission to humans, especially in areas with a high population of I. granulatus. This study successfully characterized the tick microbiome and provided the first baseline data of I. granulatus bacterial communities in Malaysia. These results support the need for way-forward research on tick-associated bacteria using NGS, focusing on medically important species toward TBD prevention.

Distribution and Prevalence of Anaplasmataceae, Rickettsiaceae and Coxiellaceae in African Ticks: A Systematic Review and Meta-Analysis

In Africa, ticks continue to be a major hindrance to the improvement of the livestock industry due to tick-borne pathogens that include Anaplasma, Ehrlichia, Rickettsia and Coxiella species. A systemic review and meta-analysis were conducted here and highlighted the distribution and prevalence of these tick-borne pathogens in African ticks. Relevant publications were searched in five electronic databases and selected using inclusion/exclusion criteria, resulting in 138 and 78 papers included in the qualitative and quantitative analysis, respectively. Most of the studies focused on Rickettsia africae (38 studies), followed by Ehrlichia ruminantium (27 studies), Coxiella burnetii (20 studies) and Anaplasma marginale (17 studies). A meta-analysis of proportions was performed using the random-effects model. The highest prevalence was obtained for Rickettsia spp. (18.39%; 95% CI: 14.23–22.85%), R. africae (13.47%; 95% CI: 2.76–28.69%), R. conorii (11.28%; 95% CI: 1.77–25.89%), A. marginale (12.75%; 95% CI: 4.06–24.35%), E. ruminantium (6.37%; 95% CI: 3.97–9.16%) and E. canis (4.3%; 95% CI: 0.04–12.66%). The prevalence of C. burnetii was low (0%; 95% CI: 0–0.25%), with higher prevalence for Coxiella spp. (27.02%; 95% CI: 10.83–46.03%) and Coxiella-like endosymbionts (70.47%; 95% CI: 27–99.82%). The effect of the tick genera, tick species, country and other variables were identified and highlighted the epidemiology of Rhipicephalus ticks in the heartwater; affinity of each Rickettsia species for different tick genera; dominant distribution of A. marginale, R. africae and Coxiella-like endosymbionts in ticks and a low distribution of C. burnetii in African hard ticks.

Substantial viral and bacterial diversity at the bat-tick interface

Ticks harbour a high diversity of viruses, bacteria and protozoa. The soft tick Carios vespertilionis (Argasidae) is a common ectoparasite of bats in the Palearctic region and is suspected to be vector and reservoir of viruses and other microbial species in bat populations, some of which may act as zoonotic agents for human disease. The Soprano pipistrelle (Pipistrellus pygmaeus, Vespertilionidae) is widely distributed in Europe, where it can be found inside or close to human habitation. We used meta-transcriptomic sequencing to determine the RNA virome and common microbiota in blood-fed C. vespertilionis ticks collected from a Soprano pipistrelle bat roosting site in south-central Sweden. Our analyses identified 16 viruses from 11 virus families, of which 15 viruses were novel. For the first time in Sweden we identified Issuk-Kul virus, a zoonotic arthropod-borne virus previously associated with outbreaks of acute febrile illness in humans. Probable bat-associated and tick-borne viruses were classified within the families Nairoviridae, Caliciviridae and Hepeviridae, while other invertebrate-associated viruses included members of the Dicistroviridae, Iflaviridae, Nodaviridae, Partitiviridae, Permutotetraviridae, Polycipiviridae and Solemoviridae. Similarly, we found abundant bacteria in C. vespertilionis, including genera with known tick-borne bacteria, such as Coxiella spp. and Rickettsia spp. These findings demonstrate the remarkable diversity of RNA viruses and bacteria present in C. vespertilionis and highlight the importance of bat-associated ectoparasite surveillance as an effective and non-invasive means to track viruses and bacteria circulating in bats and ticks.

Involvement of Microbiota in Insect Physiology: Focus on B Vitamins

Insects are highly successful in colonizing a wide spectrum of ecological niches and in feeding on a wide diversity of diets. This is notably linked to their capacity to get from their microbiota any essential component lacking in the diet such as vitamins and amino acids. Over a century of research based on dietary analysis, antimicrobial treatment, gnotobiotic rearing, and culture-independent microbe detection progressively generated a wealth of information about the role of the microbiota in specific aspects of insect fitness. Thanks to the recent increase in sequencing capacities, whole-genome sequencing of a number of symbionts has facilitated tracing of biosynthesis pathways, validation of experimental data and evolutionary analyses. This field of research has generated a considerable set of data in a diversity of hosts harboring specific symbionts or nonspecific microbiota members. Here, we review the current knowledge on the involvement of the microbiota in insect and tick nutrition, with a particular focus on B vitamin provision. We specifically question if there is any specificity of B vitamin provision by symbionts compared to the redundant yet essential contribution of nonspecific microbes. We successively highlight the known aspects of microbial vitamin provision during three main life stages of invertebrates: postembryonic development, adulthood, and reproduction.

The dynamics of the microbiome in Ixodidae are shaped by tick ontogeny and pathogens in Sarawak, Malaysian Borneo

Tick-borne diseases have recently been considered a potential emerging public health threat in Malaysia; however, fundamental studies into tick-borne pathogens and microbiome appear limited. In this study, six tick species (Ixodes granulatus, Haemaphysalis hystricis, Haemaphysalis shimoga, Dermacentor compactus, Dermacentor steini and Dermacentor atrosignatus) collected from two primary forests and an oil palm plantation in Sarawak, Malaysian Borneo, were used for microbiome analysis targeting bacterial 16S rDNA using next-generation sequencing (NGS). In addition, bacterial species were further characterized in conventional PCRs to identify potential pathogens. Sequences generated from NGS were first filtered with the Decontam package in R before subsequent microbial diversity analyses. Alpha and beta analyses revealed that the genus Dermacentor had the highest microbial diversity, and H. shimoga significantly differed in microbial composition from other tick species. Alpha and beta diversities were also significantly different between developmental stages of H. shimoga. Furthermore, we observed that some bacterial groups were significantly more abundant in certain tick species and developmental stages of H. shimoga. We tested the relative abundances using pairwise linear discriminant analysis effect size (LEfSe), which also revealed significant microbial composition differences between Borrelia-positive and Borrelia-negative I. granulatus ticks. Finally, pathogenic and potentially pathogenic bacteria circulating in different tick species, such as Rickettsia heilongjiangensis, Ehrlichia sp., Anaplasma sp. and Bartonella spp. were characterized by PCR and sequencing. Moreover, Coxiella and Francisella-like potential symbionts were identified from H. shimoga and D. steini, respectively. More studies are required to unravel the factors associated with the variations observed in this study.

Changes in the Ixodes ricinus microbiome associated with artificial tick feeding

Artificial tick feeding systems (ATFS) can be used to study tick biology and tick-pathogen interactions. Due to the long feeding duration of hard ticks, antibiotics are commonly added to the in vitro blood meal to prevent the blood from decaying. This may affect the ticks' microbiome, including mutualistic bacteria that play an important role in tick biology. This effect was examined by the consecutive feeding of Ixodes ricinus larvae, nymphs, and adults in vitro with and without the supplementation of gentamicin and in parallel on calves. DNA extracted from unfed females was analyzed by 16S rRNA sequencing. The abundance of Candidatus Midichloria mitochondrii, Rickettsia helvetica and Spiroplasma spp. was measured by qPCR in unfed larvae, nymphs, and adults. Larvae and nymphs fed on calves performed significantly better compared to both in vitro groups. Adults fed on blood supplemented with gentamicin and B vitamins had a higher detachment proportion and weight compared to the group fed with B vitamins but without gentamicin. The detachment proportion and weights of females did not differ significantly between ticks fed on calves and in vitro with gentamicin, but the fecundity was significantly higher in ticks fed on calves. 16S rRNA sequencing showed a higher microbiome species richness in ticks fed on calves compared to ticks fed in vitro. A shift in microbiome composition, with Ca. Midichloria mitochondrii as dominant species in females fed as juveniles on calves and R. helvetica as the most abundant species in females previously fed in vitro was observed. Females fed in vitro without gentamicin showed significant lower loads of Ca. M. mitochondrii compared to females fed in vitro with gentamicin and ticks fed on calves. Spiroplasma spp. were exclusively detected in female ticks fed on cattle by qPCR, but 16S rRNA sequencing results also showed a low abundance in in vitro females exposed to gentamicin. In conclusion, the employed feeding method and gentamicin supplementation affected the ticks' microbiome composition and fecundity. Since these changes may have an impact on tick biology and vector competence, they should be taken into account in studies employing ATFS.

Thermal and latitudinal patterns in pace-of-life traits are partly mediated by the gut microbiome

The integration of life-history, physiological and behavioural traits into the pace-of-life generates a powerful framework to understand trait variation in nature both along environmental gradients and in response to environmental stressors. While the gut microbiome has been hypothesized as a candidate mechanism to underlie differentiation in the pace-of-life, this has been rarely studied. We investigated the role of the gut microbiome in contributing to the differentiation in pace-of-life and in thermal adaptation between populations of Ischnura elegans damselfly larvae inhabiting warmer low latitudes and colder high latitudes. We carried out a common-garden experiment, whereby we manipulated the exposure of the damselfly larvae to two key global warming factors: 4 °C warming and a 30 °C heat wave. Comparing the bacterial composition of the food source and the bacterioplankton indicated that damselfly larvae differentially take up bacteria from the surrounding environment and have a resident and functionally relevant microbiome. The gut microbiome differed between larvae of both latitudes, and this was associated with the host's latitudinal differentiation in activity, a key pace-of-life trait. Under heat wave exposure, the gut microbial community composition of high-latitude larvae converged towards that of the low-latitude larvae, with an increase in bacteria that likely are important in providing energy to cope with the heat wave. This suggests an adaptive latitude-specific shift in the gut microbiota matching the better ability of low-latitude hosts to deal with heat extremes. In general, our study provides evidence for the gut microbiome contributing to latitudinal differentiation in both the pace-of-life and in heat adaptation in natural populations.

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.

Identification of Bacterial Communities and Tick-Borne Pathogens in Haemaphysalis spp. Collected from Shanghai, China

Ticks can carry and transmit a large number of pathogens, including bacteria, viruses and protozoa, posing a huge threat to human health and animal husbandry. Previous investigations have shown that the dominant species of ticks in Shanghai are Haemaphysalis flava and Haemaphysalis longicornis. However, no relevant investigations and research have been carried out in recent decades. Therefore, we investigated the bacterial communities and tick-borne pathogens (TBPs) in Haemaphysalis spp. from Shanghai, China. Ixodid ticks were collected from 18 sites in Shanghai, China, and identified using morphological and molecular methods. The V3-V4 hypervariable regions of the bacterial 16S rRNA gene were amplified from the pooled tick DNA samples and subject to metagenomic analysis. The microbial diversity in the tick samples was estimated using the alpha diversity that includes the observed species index and Shannon index. The Unifrac distance matrix as determined using the QIIME software was used for unweighted Unifrac Principal coordinates analysis (PCoA). Individual tick DNA samples were screened with genus-specific or group-specific nested polymerase chain reaction (PCR) for these TBPs and combined with a sequencing assay to confirm the results of the V3-V4 hypervariable regions of the bacterial 16S rRNA gene. We found H. flava and H. longicornis to be the dominant species of ticks in Shanghai in this study. Proteobacteria, Firmicutes, Bacteroidetes and Actinobacteria are the main bacterial communities of Haemaphysalis spp. The total species abundances of Proteobacteria, Firmicutes and Bacteroidetes, are 48.8%, 20.8% and 18.1%, respectively. At the level of genus analysis, H. longicornis and H. flava carried at least 946 genera of bacteria. The bacteria with high abundance include Lactobacillus, Coxiella, Rickettsia and Muribaculaceae. Additionally, Rickettsia rickettsii, Rickettsia japonica, Candidatus Rickettsia jingxinensis, Anaplasma bovis, Ehrlichia ewingii, Ehrlichia chaffeensis, Coxiella spp. and Coxiella-like endosymbiont were detected in Haemaphysalis spp. from Shanghai, China. This study is the first report of bacterial communities and the prevalence of some main pathogens in Haemaphysalis spp. from Shanghai, China, and may provide insights and evidence for bacterial communities and the prevalence of the main pathogen in ticks. This study also indicates that people and other animals in Shanghai, China, are exposed to several TBPs.

Microbiota Community Structure and Interaction Networks within Dermacentor silvarum, Ixodes persulcatus, and Haemaphysalis concinna

Ticks carry and transmit a variety of pathogens, which are very harmful to humans and animals. To characterize the microbial interactions in ticks, we analysed the microbiota of the hard ticks, Dermacentor silvarum, Ixodes persulcatus, and Haemaphysalis concinna, using 16S rRNA, showing that microbial interactions are underappreciated in terms of shaping arthropod microbiomes. The results show that the bacterial richness and microbiota structures of these three tick species had significant differences. Interestingly, the bacterial richness (Chao1 index) of all ticks decreased significantly after they became engorged. All the operational taxonomic units (OTUs) were assigned to 26 phyla, 67 classes, 159 orders, 279 families, and 627 genera. Microbial interactions in D. silvarum demonstrated more connections than in I. persulcatus and H. concinna. Bacteria with a high abundance were not important families in microbial interactions. Positive interactions of Bacteroidaceae and F_Solibacteraceae Subgroup 3 with other bacterial families were detected in all nine groups of ticks. This study provides an overview of the microbiota structure and interactions of three tick species and improves our understanding of the role of the microbiota in tick physiology and vector capacity, thus being conducive to providing basic data for the prevention of ticks and tick-borne diseases.

Hematophagy and tick-borne Rickettsial pathogen shape the microbial community structure and predicted functions within the tick vector, Amblyomma maculatum

Background

Ticks are the primary vectors of emerging and resurging pathogens of public health significance worldwide. Analyzing tick bacterial composition, diversity, and functionality across developmental stages and tissues is crucial for designing new strategies to control ticks and prevent tick-borne diseases.

Materials and methods

Here, we explored the microbial communities across the developmental timeline and in different tissues of the Gulf-Coast ticks (Amblyomma maculatum). Using a high-throughput sequencing approach, the influence of blood meal and Rickettsia parkeri, a spotted fever group rickettsiae infection in driving changes in microbiome composition, diversity, and functionality was determined.

Results

This study shows that the core microbiome of Am. maculatum comprises ten core bacterial genera. The genus Rickettsia, Francisella, and Candidatus_Midichloria are the key players, with positive interactions within each developmental stage and adult tick organ tested. Blood meal and Rickettsia parkeri led to an increase in the bacterial abundance in the tissues. According to functional analysis, the increase in bacterial numbers is positively correlated to highly abundant energy metabolism orthologs with blood meal. Correlation analysis identified an increase in OTUs identified as Candidatus Midichloria and a subsequent decrease in Francisella OTUs in Rickettsia parkeri infected tick stages and tissues. Results demonstrate the abundance of Rickettsia and Francisella predominate in the core microbiome of Am. maculatum, whereas Candidatus_Midichloria and Cutibacterium prevalence increase with R. parkeri-infection. Network analysis and functional annotation suggest that R. parkeri interacts positively with Candidatus_Midichloria and negatively with Francisella.

Conclusion

We conclude that tick-transmitted pathogens, such as R. parkeri establishes infection by interacting with the core microbiome of the tick vector.

Tropical and Temperate Lineages of Rhipicephalus sanguineus s.l. Ticks (Acari: Ixodidae) Host Different Strains of Coxiella-like Endosymbionts

Nonpathogenic bacteria likely play important roles in the biology and vector competence of ticks and other arthropods. Coxiella, a gram-negative gammaproteobacterium, is one of the most commonly reported maternally inherited endosymbionts in ticks and has been associated with over 40 tick species. Species-specific Coxiella-like endosymbionts (CLEs) have been reported in the brown dog tick, Rhipicephalus sanguineus sensu lato (Acari: Ixodidae), throughout the world, while recent research suggests low Coxiella diversity among tick species. We investigated CLE diversity among R. sanguineus s.l. ticks across Arizona. We detected 37 recurrent sequence variants (SVs) of the symbiont, indicating greater diversity in these symbiotic bacteria than previously reported. However, two SVs accounted for the vast majority of 16S rRNA amplicon reads. These two dominant CLEs were both closely related to Candidatus C. mudrowiae, an identified symbiont of Rhipicephalus turanicus ticks. One strain strongly associated with the tropical lineage of R. sanguineus s.l. while the other was found almost exclusively in the temperate lineage, supporting the conclusion that CLEs are primarily vertically transmitted. However, occasional mismatches between tick lineage and symbiont SV indicate that horizontal symbiont transfer may occur, perhaps via cofeeding of ticks from different lineages on the same dog. This study advances our understanding of CLE diversity in Rh. sanguineus s.l.

What do we know about the microbiome of I. ricinus?

I. ricinus is an obligate hematophagous parasitic arthropod that is responsible for the transmission of a wide range of zoonotic pathogens including spirochetes of the genus Borrelia, Rickettsia spp., C. burnetii, Anaplasma phagocytophilum and Francisella tularensis, which are part the tick´s microbiome. Most of the studies focus on "pathogens" and only very few elucidate the role of "non-pathogenic" symbiotic microorganisms in I. ricinus. While most of the members of the microbiome are leading an intracellular lifestyle, they are able to complement tick´s nutrition and stress response having a great impact on tick´s survival and transmission of pathogens. The composition of the tick´s microbiome is not consistent and can be tied to the environment, tick species, developmental stage, or specific organ or tissue. Ovarian tissue harbors a stable microbiome consisting mainly but not exclusively of endosymbiotic bacteria, while the microbiome of the digestive system is rather unstable, and together with salivary glands, is mostly comprised of pathogens. The most prevalent endosymbionts found in ticks are Rickettsia spp., Ricketsiella spp., Coxiella-like and Francisella-like endosymbionts, Spiroplasma spp. and Candidatus Midichloria spp. Since microorganisms can modify ticks' behavior, such as mobility, feeding or saliva production, which results in increased survival rates, we aimed to elucidate the potential, tight relationship, and interaction between bacteria of the I. ricinus microbiome. Here we show that endosymbionts including Coxiella-like spp., can provide I. ricinus with different types of vitamin B (B2, B6, B7, B9) essential for eukaryotic organisms. Furthermore, we hypothesize that survival of Wolbachia spp., or the bacterial pathogen A. phagocytophilum can be supported by the tick itself since coinfection with symbiotic Spiroplasma ixodetis provides I. ricinus with complete metabolic pathway of folate biosynthesis necessary for DNA synthesis and cell division. Manipulation of tick´s endosymbiotic microbiome could present a perspective way of I. ricinus control and regulation of spread of emerging bacterial pathogens.

Molecular detection of Coxiella-like endosymbionts in Rhipicephalus microplus from north India

Apart from the tick-borne pathogens affecting human and animal health, ticks also harbor various non-pathogenic endosymbionts with dynamic ecological interactions. These endosymbionts are unexplored from the Indian ticks; hence this pilot study was conducted. Seventy-nine ticks were collected from Nainital district of Uttarakhand state of north India and were identified as Rhipicephalus microplus morphologically and by molecular analysis. PCR and sequence analysis were carried out to detect the presence of Rickettsia-like, Coxiella-like and Francisella-like endosymbionts in these ticks. Based on the partial 16S rRNA gene sequence, Coxiella-like endosymbiont (CLE) was detected in the adult and other life-cycle stages of ticks with 96.6-97.7% nucleotide sequence identity with the published CLE sequences from GenBank. The phylogenetic analysis revealed that the CLE from R. microplus were clustered with the CLE from other Rhipicephalus species. All these CLE formed distinct clades from the pathogenic Coxiella burnetii. None of the tick samples was found positive for Rickettsia-like and Francisella-like endosymbionts in the present study. We also demonstrated the vertical transmission of CLE from surface sterilized and laboratory reared fully engorged adult females to the eggs and the larvae. However, large scale studies are to be conducted to detect various endosymbionts and endosymbiont-tick associations in the Indian tick species and to explore these associations for tick and tick-borne disease control.

Wild Hedgehogs and Their Parasitic Ticks Coinfected with Multiple Tick-Borne Pathogens in Jiangsu Province, Eastern China

The increasing awareness of emerging tickborne pathogens (TBPs) has inspired much research. In the present study, the coinfections of TBPs both in ticks and their wild hedgehog hosts in Jiangsu province, Eastern China were determined by metagenome next-generation sequencing and nested PCR. As a result, Rickettsia japonica (81.1%), novel Rickettsia sp. SFGR-1 (5.1%), Anaplasma bovis (12%), A. platys (6.3%), novel Ehrlichia spp. Ehr-1 (16%) and Ehr-2 (0.6%), E. ewingii-like strain (0.6%), Coxiella burnetii (10.9%), and a novel Coxiella-like endosymbiont (CLE) strain (61.1%) were detected in Haemaphysalis flava ticks. A. bovis (43.8%), Ehrlichia sp. Ehr-1 (83.3%), and C. burnetii (80%) were detected in Erinaceus amurensis hedgehogs. Coinfection rates with various TBPs were 71.5% and 83.3% in ticks and hedgehogs, respectively, both with double-pathogen/endosymbiont coinfection rates over 50%. We found the following. (i) Er. amurensis hedgehogs seem to contribute to the natural cycles of R. japonica, A. bovis, Ehrlichia sp., and C. burnetii and may be reservoirs of them except for R. japonica, and A. bovis is proved to infect hedgehogs for the first time. (ii) H. flava is proved to harbor various TBPs as a reservoir host, including CLE identified for the first time, which could inhibit coinfection of C. burnetii while promoting that of Rickettsia spp. in H. flava. (iii) Four novel TBP species were identified. This study provides useful epidemiological information crucial for assessing the potential infection risks to humans, thus benefiting the development of strategies to prevent and control tick-borne diseases. IMPORTANCE In the present study, we found the following. (i) Er. amurensis hedgehogs seem to contribute to the natural cycles of R. japonica, A. bovis, Ehrlichia sp., and C. burnetii and may be reservoirs of them except for R. japonica, and A. bovis is proved to infect hedgehogs for the first time. (ii) H. flava is proved to harbor various tickborne pathogens (TBPs) as a reservoir host, including Coxiella-like endosymbiont (CLE) identified for the first time, which could inhibit coinfection of C. burnetii while promoting that of Rickettsia spp. in H. flava. (iii) Four novel TBP species were identified. This study provides useful epidemiological information on TBPs harbored and transmitted by ticks and their hosts, for assessing the potential infection risks to humans, thus benefiting the developing strategies for tick-borne diseases prevention and control.

Quantitative microbial population study reveals geographical differences in bacterial symbionts of Ixodes ricinus

BACKGROUND

Ixodes ricinus ticks vector pathogens that cause serious health concerns. Like in other arthropods, the microbiome may affect the tick's biology, with consequences for pathogen transmission. Here, we explored the bacterial communities of I. ricinus across its developmental stages and six geographic locations by the 16S rRNA amplicon sequencing, combined with quantification of the bacterial load.

RESULTS

A wide range of bacterial loads was found. Accurate quantification of low microbial biomass samples permitted comparisons to high biomass samples, despite the presence of contaminating DNA. The bacterial communities of ticks were associated with geographical location rather than life stage, and differences in Rickettsia abundance determined this association. Subsequently, we explored the geographical distribution of four vertically transmitted symbionts identified in the microbiome analysis. For that, we screened 16,555 nymphs from 19 forest sites for R. helvetica, Rickettsiella spp., Midichloria mitochondrii, and Spiroplasma ixodetis. Also, the infection rates and distributions of these symbionts were compared to the horizontally transmitted pathogens Borrelia burgdorferi sensu lato, Anaplasma phagocytophilum, and Neoehrlichia mikurensis. The infection rates of all vertically transmitted symbionts differed between the study sites, and none of the symbionts was present in all tested ticks suggesting a facultative association with I. ricinus. The proportions in which symbionts occurred in populations of I. ricinus were highly variable, but geographically close study sites expressed similar proportions. These patterns were in contrast to what we observed for horizontally transmitted pathogens. Lastly, nearly 12% of tested nymphs were free of any targeted microorganisms, which is in line with the microbiome analyses.

CONCLUSIONS

Our results show that the microbiome of I. ricinus is highly variable, but changes gradually and ticks originating from geographically close forest sites express similar bacterial communities. This suggests that geography-related factors affect the infection rates of vertically transmitted symbionts in I. ricinus. Since some symbionts, such as R. helvetica can cause disease in humans, we propose that public health investigations consider geographical differences in its infection rates.

Growth dynamics and tissue localization of a Coxiella-like endosymbiont in the tick Haemaphysalis longicornis

A Coxiella-like endosymbiont (Coxiella-LE hereinafter) stably infects and influences Haemaphysalis longicornis development, indicating a mutualistic relationship of Coxiella-LE and ticks. To further elucidate the patterns of growth dynamics and tissue localization of Coxiella-LE in H. longicornis, 16S rRNA high-throughput sequencing, quantitative PCR (qPCR), and fluorescence in situ hybridization (FISH) were used in this study. The density of Coxiella-LE varied among different tick life stages, and fed female ticks had the highest density, followed by unfed female and unfed larval ticks. In the four organs that were dissected from fed female ticks, the ovary carried the highest density of Coxiella-LE, which was significantly different from salivary glands, midgut and Malpighian tubules. The high abundance of Coxiella-LE in fed female ticks and in the ovaries of fed female ticks in the bacterial microbiota analyses further confirmed that Coxiella-LE rapidly proliferates in the ovary after blood feeding. The ovaries continued to develop after engorgement and oviposition began on day 5, with a significant decrease in the density of Coxiella-LE in the ovaries occurring on day 7. FISH results indicated that Coxiella-LE is mainly colonized in the cytoplasm of the oocyte and proliferates with oogenesis. Coxiella-LE was expelled from the body with the mature oocyte, ensuring its vertical transmission. In the Malpighian tubules at different days after engorgement, the white flocculent materials were increasing, and the density of Coxiella-LE raised significantly on day 7. Unlike the localization pattern in the ovary, Coxiella-LE was initially distributed in a mass and continually increased during the development of Malpighian tubules until it filled the Malpighian tubules. These findings provide new insights on the growth dynamics and tissue localization of Coxiella-LE in ticks and are useful for further investigation on the interactions of symbiont and ticks .

Co-Occurrence of Francisella, Spotted Fever Group Rickettsia, and Midichloria in Avian-Associated Hyalomma rufipes

The migratory behavior of wild birds contributes to the geographical spread of ticks and their microorganisms. In this study, we aimed to investigate the dispersal and co-occurrence of Francisella and spotted fever group Rickettsia (SFGR) in ticks infesting birds migrating northward in the African-Western Palaearctic region (AWPR). Birds were trapped with mist nests across the Mediterranean basin during the 2014 and 2015 spring migration. In total, 575 ticks were collected from 244 birds. We screened the ticks for the species Francisella tularensis, the genus Francisella, and SFGR by microfluidic real-time PCR. Confirmatory analyses and metagenomic sequencing were performed on tick samples that putatively tested positive for F. tularensis during initial screenings. Hyalomma rufipes was the most common tick species and had a high prevalence of Francisella, including co-occurrence of Francisella and SFGR. Metagenomic analysis of total DNA extracted from two H. rufipes confirmed the presence of Francisella, Rickettsia, and Midichloria. Average nucleotide identity and phylogenetic inference indicated the highest identity of the metagenome-assembled genomes to a Francisella-like endosymbiont (FLE), Rickettsia aeschlimannii, and Midichloria mitochondrii. The results of this study suggest that (i) FLE- and SFGR-containing ticks are dispersed by northbound migratory birds in the AWPR, (ii) H. rufipes likely is not involved in transmission of F. tularensis in the AWPR, and (iii) a dual endosymbiosis of FLEs and Midichloria may support some of the nutritional requirements of H. rufipes.

Coxiella Endosymbiont of Rhipicephalus microplus Modulates Tick Physiology With a Major Impact in Blood Feeding Capacity

In the past decade, metagenomics studies exploring tick microbiota have revealed widespread interactions between bacteria and arthropods, including symbiotic interactions. Functional studies showed that obligate endosymbionts contribute to tick biology, affecting reproductive fitness and molting. Understanding the molecular basis of the interaction between ticks and their mutualist endosymbionts may help to develop control methods based on microbiome manipulation. Previously, we showed that Rhipicephalus microplus larvae with reduced levels of Coxiella endosymbiont of R. microplus (CERM) were arrested at the metanymph life stage (partially engorged nymph) and did not molt into adults. In this study, we performed a transcriptomic differential analysis of the R. microplus metanymph in the presence and absence of its mutualist endosymbiont. The lack of CERM resulted in an altered expression profile of transcripts from several functional categories. Gene products such as DA-P36, protease inhibitors, metalloproteases, and evasins, which are involved in blood feeding capacity, were underexpressed in CERM-free metanymphs. Disregulation in genes related to extracellular matrix remodeling was also observed in the absence of the symbiont. Taken together, the observed alterations in gene expression may explain the blockage of development at the metanymph stage and reveal a novel physiological aspect of the symbiont-tick-vertebrate host interaction.

First insights into the microbiome of Tunisian Hyalomma ticks gained through next-generation sequencing with a special focus on H. scupense

Ticks are one of the most important vectors of several pathogens affecting humans and animals. In addition to pathogens, ticks carry diverse microbiota of symbiotic and commensal microorganisms. In this study, we have investigated the first Tunisian insight into the microbial composition of the most dominant Hyalomma species infesting Tunisian cattle and explored the relative contribution of tick sex, life stage, and species to the diversity, richness and bacterial species of tick microbiome. In this regard, next generation sequencing for the 16S rRNA (V3-V4 region) of tick bacterial microbiota and metagenomic analysis were established. The analysis of the bacterial diversity reveals that H. marginatum and H. excavatum have greater diversity than H. scupense. Furthermore, microbial diversity and composition vary according to the tick’s life stage and sex in the specific case of H. scupense. The endosymbionts Francisella, Midichloria mitochondrii, and Rickettsia were shown to be the most prevalent in Hyalomma spp. Rickettsia, Francisella, Ehrlichia, and Erwinia are the most common zoonotic bacteria found in Hyalomma ticks. Accordingly, Hyalomma ticks could represent potential vectors for these zoonotic bacterial agents.

Ecological Contacts and Host Specificity Promote Replacement of Nutritional Endosymbionts in Ticks

Symbiosis with vitamin-provisioning microbes is essential for the nutrition of animals with some specialized feeding habits. While coevolution favors the interdependence between symbiotic partners, their associations are not necessarily stable: Recently acquired symbionts can replace ancestral symbionts. In this study, we demonstrate successful replacement by Francisella-like endosymbionts (-LE), a group of B-vitamin-provisioning endosymbionts, across tick communities driven by horizontal transfers. Using a broad collection of Francisella-LE-infected tick species, we determined the diversity of Francisella-LE haplotypes through a multi-locus strain typing approach and further characterized their phylogenetic relationships and their association with biological traits of their tick hosts. The patterns observed showed that Francisella-LE commonly transfer through similar ecological networks and geographic distributions shared among different tick species and, in certain cases, through preferential shuffling across congeneric tick species. Altogether, these findings reveal the importance of geographic, ecological, and phylogenetic proximity in shaping the replacement pattern in which new nutritional symbioses are initiated.

Novel symbionts and potential human pathogens excavated from argasid tick microbiomes that are shaped by dual or single symbiosis

Research on vector-associated microbiomes has been expanding due to increasing emergence of vector-borne pathogens and awareness of the importance of symbionts in the vector physiology. However, little is known about microbiomes of argasid (or soft-bodied) ticks due to limited access to specimens. We collected four argasid species (Argas japonicus, Carios vespertilionis, Ornithodoros capensis, and Ornithodoros sawaii) from the nests or burrows of their vertebrate hosts. One laboratory-reared argasid species (Ornithodoros moubata) was also included. Attempts were then made to isolate and characterize potential symbionts/pathogens using arthropod cell lines. Microbial community structure was distinct for each tick species. Coxiella was detected as the predominant symbiont in four tick species where dual symbiosis between Coxiella and Rickettsia or Coxiella and Francisella was observed in C. vespertilionis and O. moubata, respectively. Of note, A. japonicus lacked Coxiella and instead had Occidentia massiliensis and Thiotrichales as alternative symbionts. Our study found strong correlation between tick species and life stage. We successfully isolated Oc. massiliensis and characterized potential pathogens of genera Ehrlichia and Borrelia. The results suggest that there is no consistent trend of microbiomes in relation to tick life stage that fit all tick species and that the final interpretation should be related to the balance between environmental bacterial exposure and endosymbiont ecology. Nevertheless, our findings provide insights on the ecology of tick microbiomes and basis for future investigations on the capacity of argasid ticks to carry novel pathogens with public health importance.

The Symbiotic Continuum Within Ticks: Opportunities for Disease Control

Among blood-sucking arthropods, ticks are recognized as being of prime global importance because of their role as vectors of pathogens affecting human and animal health. Ticks carry a variety of pathogenic, commensal, and symbiotic microorganisms. For the latter, studies are available concerning the detection of endosymbionts, but their role in the physiology and ecology of ticks remains largely unexplored. This review paper focuses on tick endosymbionts of the genera Coxiella, Rickettsia, Francisella, Midichloria, and Wolbachia, and their impact on ticks and tick-pathogen interactions that drive disease risk. Tick endosymbionts can affect tick physiology by influencing nutritional adaptation, fitness, and immunity. Further, symbionts may influence disease ecology, as they interact with tick-borne pathogens and can facilitate or compete with pathogen development within the vector tissues. Rickettsial symbionts are frequently found in ticks of the genera of Ixodes, Amblyomma, and Dermacentor with relatively lower occurrence in Rhipicephalus, Haemaphysalis, and Hyalomma ticks, while Coxiella-like endosymbionts (CLEs) were reported infecting almost all tick species tested. Francisella-like endosymbionts (FLEs) have been identified in tick genera such as Dermacentor, Amblyomma, Ornithodoros, Ixodes, and Hyalomma, whereas Wolbachia sp. has been detected in Ixodes, Amblyomma, Hyalomma, and Rhipicephalus tick genera. Notably, CLEs and FLEs are obligate endosymbionts essential for tick survival and development through the life cycle. American dog ticks showed greater motility when infected with Rickettsia, indirectly influencing infection risk, providing evidence of a relationship between tick endosymbionts and tick-vectored pathogens. The widespread occurrence of endosymbionts across the tick phylogeny and evidence of their functional roles in ticks and interference with tick-borne pathogens suggests a significant contribution to tick evolution and/or vector competence. We currently understand relatively little on how these endosymbionts influence tick parasitism, vector capacity, pathogen transmission and colonization, and ultimately on how they influence tick-borne disease dynamics. Filling this knowledge gap represents a major challenge for future research.

Current debates and advances in tick microbiome research

The main importance of ticks resides in their ability to harbor pathogens that can be transmitted to terrestrial vertebrates including humans. Recently, studies have focused on the taxonomic and functional composition of the tick microbiome, its microbial diversity and variation under different factors including tick species, sex, and environment among others. Of special interest are the interactions between the tick, the microbiome and pathogens since tick microbiome can influence pathogen colonization within the tick vector, and potentially, transmission to the vertebrate host. In this review, we tackled a synthesis on the growing field of tick microbiomes. We focus on the current state of tick microbiome research, addressing controversial and hotly debated topics and advances in the precise manipulation of tick microbiome. Furthermore, we discuss the innovative anti-tick microbiota vaccines as a possible tool for microbiome modulation and thus, control of tick-borne diseases. Deciphering tick-microbiome pathogen interactions can spur new strategies to control tick-borne diseases via modulation of tick microbiome.

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Whether the diversity observed in tick microbiomes concerns the biology or the methodology remains an open question.

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Tick immunity must play a major role in selecting ‘who stays and who leaves’ the microbiome.

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Anti-tick microbiota vaccines can target specific bacteria and subsequently modulate tick microbiome.

Illuminating the bacterial microbiome of Australian ticks with 16S and Rickettsia-specific next-generation sequencing

Next-generation sequencing (NGS) studies show that mosquito and tick microbiomes influence the transmission of pathogens, opening new avenues for vector-borne pathogen control. Recent microbiological studies of Australian ticks highlight fundamental knowledge gaps of tick-borne agents. This investigation explored the composition, diversity and prevalence of bacteria in Australian ticks (n = 655) from companion animals (dogs, cats and horses). Bacterial 16S NGS was used to identify most bacterial taxa and a Rickettsia-specific NGS assay was developed to identify Rickettsia species that were indistinguishable at the V1-2 regions of 16S. Sanger sequencing of near full-length 16S was used to confirm whether species detected by 16S NGS were novel. The haemotropic bacterial pathogens Anaplasma platys, Bartonella clarridgeiae, “Candidatus Mycoplasma haematoparvum” and Coxiella burnetii were identified in Rhipicephalus sanguineus (s.l.) from Queensland (QLD), Western Australia, the Northern Territory (NT), and South Australia, Ixodes holocyclus from QLD, Rh. sanguineus (s.l.) from the NT, and I. holocyclus from QLD, respectively. Analysis of the control data showed that cross-talk compromises the detection of rare species as filtering thresholds for less abundant sequences had to be applied to mitigate false positives. A comparison of the taxonomic assignments made with 16S sequence databases revealed inconsistencies. The Rickettsia-specific citrate synthase gene NGS assay enabled the identification of Rickettsia co-infections with potentially novel species and genotypes most similar (97.9–99.1%) to Rickettsia raoultii and Rickettsia gravesii. “Candidatus Rickettsia jingxinensis” was identified for the first time in Australia. Phylogenetic analysis of near full-length 16S sequences confirmed a novel Coxiellaceae genus and species, two novel Francisella species, and two novel Francisella genotypes. Cross-talk raises concerns for the MiSeq platform as a diagnostic tool for clinical samples. This study provides recommendations for adjustments to Illuminaʼs 16S metagenomic sequencing protocol that help track and reduce cross-talk from cross-contamination during library preparation. The inconsistencies in taxonomic assignment emphasise the need for curated and quality-checked sequence databases.

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Bacterial pathogens identified in ticks from companion animals with 16S NGS.

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Sanger sequencing confirmed novel Coxiellaceae gen. sp. and Francisella.

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“Candidatus Rickettsia jingxinensis” was identified with Rickettsia-specific NGS.

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Comparison of taxonomic assignments in 16S sequence databases revealed errors.

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Modifications to the 16S metagenomic library protocol (Illumina) are provided.