Microbial communities and symbionts in the hard tick Haemaphysalis longicornis (Acari: Ixodidae) from north China

Distribution characteristics and influencing factors of Haemaphysalis longicornis around goat sheds in Jinan city, East China

As one of the most important disease vectors worldwide, ticks can transmit a number of pathogenic organisms to humans and domestic animals and cause a variety of important natural focal diseases and zoonoses. Domestic livestock play a vital role in the dispersal of ticks from the field environment to the human settlement, contributing to the prevalence of tick-borne diseases. Identification of the tick control region could contribute a vital role in strategic planning and cost-effective tick control measures. However, little is known about the spatial distribution characteristics of ticks around livestock sheds, which will lead to abusage and overuse of insecticides. Therefore, this study aimed to explore spatial distribution characteristics and correlation factors of ticks around goat sheds. A total of 3898 ticks were collected from eight goat sheds from April to June in Jinan city. All the sampled ticks belonged to the same species, namely Haemaphysalis longicornis, and 88.8% of them were nymphs. A significant positive correlation was noted between free-living ticks and parasitic ticks (r = 0.411, P < 0.001). However, there was a significant negative correlation between number of free-living ticks and distance from the goat sheds (r = -0.622, P < 0.001). Within 20 m from the goat sheds, 2211 ticks were collected respectively, representing 56.7% of the total free-living ticks. At a distance of 30 m, 57.6% decline in the tick density was found with a significant difference (q = 5.534, P < 0.001). In conclusion, focusing control efforts near the goat sheds should be recommend for tick prevention and control.

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.

The toxicity of the monoterpenes from lemongrass is mitigated by the detoxifying symbiosis of bacteria and fungi in the tick Haemaphysalis longicornis

The entry mode of terpenes into the atmosphere is via volatilization of hydrocarbons from foliage over heavily forested areas besides entering the environment through surface water runoff. Some monoterpenes in essential oils are phytotoxins, acting as plant chemical defenses against bacteria or fungi infections and plant-eating insects. For organisms to survive, their enzymatic systems are activated in response to an assault by potentially harmful compounds. Certain bacterial and fungal genera have developed special abilities to transform toxic terpenes into less toxic derivatives. Here, we investigated the response of the bacterial and fungal community in Haemaphysalis longicornis exposed to Cymbopogon citratus (lemongrass) essential oil (EO) and citronellal. Sequencing of bacterial 16S rRNA and fungal ITS1 regions on an Illumina NovaSeq PE250 sequencing platform was performed for H. longicornis tick samples treated with 15 and 20 mg/mL of lemongrass essential oil and citronellal. The diversity recorded in samples treated with C. citratus EO was higher in comparison to those treated with citronellal but significantly lower in the control samples as reflected by the Shannon diversity index. All major H. longicornis bacterial phyla, including Proteobacteria (93.81 %), Firmicutes (2.58 %), and Bacteroidota (0.99 %) were detected. A switch of dominance from Coxiella to Pseudomonas, which has high biotransformation capacity, was observed in the bacterial community, whereas the phylum Ascomycota (Genera: Aspergillus, Archaeorhizomyces, Alternaria, and Candida) dominated in the fungal community indicating detoxifying symbiosis. Other significantly abundant bacterial genera include Ralstonia, Acinetobacter, Vibrio, and Pseudoalteromonas, while Ganoderma and Trichosporon (yeasts) spp. represented the fungi Basidiomycota. This study expanded the understanding of enzymatic modification of phytotoxic substances by microorganisms, which could provide deeper insights into the mitigation of harmful phytotoxins and the synthesis of eco-friendly derivatives for the control of ticks.

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 .

Bacterial microbiota analysis demonstrates that ticks can acquire bacteria from habitat and host blood meal

Ticks have a diversity of habitats and host blood meals. Whether and how factors such as tick developmental stages, habitats and host blood meals affect tick bacterial microbiota is poorly elucidated. In the present study, we investigated the bacterial microbiotas of the hard tick Haemaphysalis longicornis, their blood meals and habitats using 16S rRNA gene high-throughput sequencing. The bacterial richness and diversity in ticks varied depending on the tick developmental stage and feeding status. Results showed that fed ticks present a higher bacterial richness suggesting that ticks may acquire bacteria from blood meals. The significant overlap of the bacteria of fed ticks and the host blood also supports this possibility. Another possibility is that blood meals can stimulate the proliferation of certain bacteria. However, most shared bacteria cannot transmit throughout the tick life cycle, as they were not present in tick eggs. The most shared bacteria between ticks and habitats are members of the genera Staphylococcus, Pseudomonas, Enterobacter, Acinetobacter and Stenotrophomonas, suggesting that these environmental bacteria cannot be completely washed away and can be acquired by ticks. The predominant proportion of Coxiella in fed females further demonstrates that this genus is involved in H. longicornis physiology, such as feeding activity and nutritional provision. These findings further reveal that the bacterial composition of ticks is influenced by a variety of factors and will help in subsequent studies of the function of these bacteria.

Comparative Proteomics of Coxiella like Endosymbionts (CLEs) in the Symbiotic Organs of Rhipicephalus sanguineus Ticks

Maternally transmitted obligatory endosymbionts are found in the female gonads as well as in somatic tissue and are expected to provide missing metabolite to their hosts. These deficiencies are presumably complemented through specific symbiotic microorganisms such as Coxiella-like endosymbionts (CLEs) of Rhipicephalus ticks. CLEs are localized in specialized host tissue cells within the Malpighian tubules (Mt) and the ovaries (Ov) from which they are maternally transmitted to developing oocytes. These two organs differ in function and cell types, but the role of CLEs in these tissues is unknown. To probe possible functions of CLEs, comparative proteomics was performed between Mt and Ov of R. sanguineus ticks. Altogether, a total of 580 and 614 CLE proteins were identified in Mt and Ov, respectively. Of these, 276 CLE proteins were more abundant in Mt, of which 12 were significantly differentially abundant. In Ov, 290 CLE proteins were more abundant, of which 16 were significantly differentially abundant. Gene Ontology analysis revealed that most of the proteins enriched in Mt are related to cellular metabolic functions and stress responses, whereas in Ov, the majority were related to cell proliferation suggesting CLEs function differentially and interdependently with host requirements specific to each organ. The results suggest Mt CLEs provide essential nutrients to its host and Ov CLEs promote proliferation and vertical transmission to tick progeny. IMPORTANCE Here we compare the Coxiella-like endosymbionts (CLEs) proteomes from Malpighian tubule (Mt) and the ovaries (Ov) of the brown dog tick Rhipicephalus sanguineus. Our results support the hypothesis that CLEs function interdependently with host requirements in each of the organs. The different functional specificity of CLE in the same host suggest that metabolic capabilities evolved according to the constrains imposed by the specific organ function and requirements. Our findings provide specific CLE protein targets that can be useful for future studies of CLE biology with a focus on tick population control.

iSeq 100 for metagenomic pathogen screening in ticks

BACKGROUND

Ticks are blood-sucking ectoparasites that play a pivotal role in the transmission of various pathogens to humans and animals. In Korea, Haemaphysalis longicornis is the predominant tick species and is recognized as the vector of pathogens causing various diseases such as babesiosis, borreliosis, rickettsiosis, and severe fever with thrombocytopenia syndrome.

METHODS

In this study, the targeted high-throughput sequencing of the 16S rRNA V4 region was performed using the state-of-the-art sequencing instrument, iSeq 100, to screen bacterial pathogens in H. longicornis, and the findings were compared with those using conventional PCR with specific primers. Microbiome analyses were performed with EzBioCloud, a commercially available ChunLab bioinformatics cloud platform. ANOVA-Like Differential Expression tool (ALDEx2) was used for differential abundance analysis.

RESULTS

Rickettsia spp. were detected in 16 out of 37 samples using iSeq 100, and this was confirmed using a PCR assay. In the phylogenetic analysis using gltA and ompA sequences of the detected Rickettsia, the highest sequence similarity was found with 'Candidatus Rickettsia jingxinensis' isolate Xian-Hl-79, 'Ca. R. jingxinensis' isolate F18, and 'Ca. R. longicornii' isolate ROK-HL727. In the microbiome study, Coxiella AB001519, a known tick symbiont, was detected in all 37 tick samples. Actinomycetospora chiangmaiensis was more abundant in Rickettsia-positive samples than in Rickettsia-negative samples.

CONCLUSIONS

In this study, iSeq 100 was used to investigate the microbiome of H. longicornis, and the potentially pathogenic Rickettsia strain was detected in 16 out of 37 ticks. We believe that this approach will aid in large-scale pathogen screening of arthropods to be used in vector-borne disease control programs.

Metagenomic deep sequencing obtains taxonomic and functional profiles of Haemaphysalis longicornis that vary in response to different developmental stages and sexes

Ticks can transmit numerous pathogens and harbor diverse microbial communities. Considerable progress has been made in the characterization of the bacterial profiles of ticks, whereas other members of tick microbiota (such as fungi and viruses) and the functional characteristics of ticks warrant further exploration. To investigate the taxonomic and functional profiles and explore potential pathogens they were carrying, samples of different developmental stages and of both sexes of Haemaphysalis longicornis were collected in the present study and the metagenomic deep sequencing method was applied. Metagenomic deep sequencing results revealed that bacteria were predominant, followed by fungi, viruses, archaea and metazoans. Proteobacteria was the dominant phylum in the microbiota of H. longicornis. The abundance of microbial species varied significantly among groups, the bacteria of nymphs and female adults demonstrated unique characteristics, and the microbial community of males overlapped with those of nymphs and females. Functional annotation results demonstrated that the metagenomic sequences of the three groups were classified under metabolism, genetic information processing, environmental information processing and cellular processes. Differences in functional characteristics were observed in both the pathways composition and abundance of carbohydrate-active enzymes. Furthermore, whole metagenome sequencing helped to elucidate the diversity of pathogens carried by H. longicornis, which may facilitate further research attempting to prevent and control tick-borne diseases.

Molecular genetic analysis and clinical characterization of Rickettsia species isolated from the Republic of Korea in 2017

Rickettsia sp. CNH17-7 was isolated from patients' blood and identified by gene analysis as a species distinct from Rickettsia japonica. In addition, similar rickettsial infection was confirmed in two species (Haemaphysalis longicornis and Ixodes nipponensis) of ticks and rodents in northeastern and southwestern provinces, Republic of Korea. Subsequently, the analysis of 16S rRNA, ompA, ompB and sca4 genes of isolate CNH17-7 revealed 100%, 99.68%, 99.57% and 99.44% sequence similarity with Rickettsia sp. HlR/D91 and Candidatus R. longicornii ROK-HL727. In this study, we report the isolation of a new Rickettsia sp. CNH17-7 and infection of different types of ticks with the same rickettsial agents.

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.

Genetic diversity of Haemaphysalis longicornis from China and molecular detection of Rickettsia

The tick Haemaphysalis longicornis (Neumann) (Acari, Ixodidae) is distributed throughout China and is the most notorious blood feeding ectoparasite of livestock. Haemaphysalis longicornis can transmit a large number of pathogens that cause human infectious diseases, such as Rickettsia spp. Here, we characterized the genetic structure of H. longicornis and tested for the presence of Rickettsia spp. from five regions in China. Analysis of the two mitochondrial marker sequences (16S rRNA and COI) and the nuclear sequence (ITS2) showed that the overall level of nucleotide diversity was low and the variability did not differ among the five regions. From the five locations, the infection rates of Rickettsia species ranged from 0 to 65%. The nucleotide diversities of the high-infected group were lower than those of the low- and uninfected group. And in neutrality tests for the high-infected group based on COI sequences, the Tajima's D and Fu's FS were coincidentally < 0 and significant, whereas they were closer to zero and non-significant in low- and uninfected groups.

Microbial diversity in the tick Argas japonicus (Acari: Argasidae) with a focus on Rickettsia pathogens

The soft tick Argas japonicus mainly infests birds and can cause human dermatitis; however, no pathogen has been identified from this tick species in China. In the present study, the microbiota in A. japonicus collected from an epidemic community was explored, and some putative Rickettsia pathogens were further characterized. The results obtained indicated that bacteria in A. japonicus were mainly ascribed to the phyla Proteobacteria, Firmicutes and Actinobacteria. At the genus level, the male A. japonicus harboured more diverse bacteria than the females and nymphs. The bacteria Alcaligenes, Pseudomonas, Rickettsia and Staphylococcus were common in nymphs and adults. The abundance of bacteria belonging to the Rickettsia genus in females and males was 7.27% and 10.42%, respectively. Furthermore, the 16S rRNA gene of Rickettsia was amplified and sequenced, and phylogenetic analysis revealed that 13 sequences were clustered with the spotted fever group rickettsiae (Rickettsia heilongjiangensis and Rickettsia japonica) and three were clustered with Rickettsia limoniae, which suggested that the characterized Rickettsia in A. japonicus were novel putative pathogens and also that the residents were at considerable risk for infection by tick-borne pathogens.

Characterization of the bacterial community in Haemaphysalis longicornis (Acari: Ixodidae) throughout developmental stages

As one of the most important vectors, Haemaphysalis longicornis can transmit a variety of pathogens and is widely distributed in China. It has been reported that the bacterial community in ticks can impact tick fitness, development, and reproduction and even the transmission of tick-borne pathogens. In this study, bacterial diversity across all developmental stages (eggs, larvae, nymphs and adults) of H. longicornis was investigated using high-throughput sequencing technology. The results demonstrated that Proteobacteria was the dominant phylum and that Coxiella was the most abundant bacterial genus across all the samples. Alpha diversity analysis demonstrated that the eggs had the highest bacterial richness and diversity, and the bacterial community of the larvae was found to be similar to that of the eggs. However, there was a rapid increase in the relative abundance of Coxiella upon development of larvae to nymphs. Females exhibited the lowest bacterial diversity, and the proportion of Coxiella decreased from 85% in females to 45% in males. Our results suggest that H. longicornis lost most of the bacteria present in the early developmental stages and re-established the bacterial community after bloodmeals and molting.

Characterization of microbiota diversity of field-collected Haemaphysalis longicornis (Acari: Ixodidae) with regard to sex and blood meals

Haemaphysalis longicornis is a prominent tick species in China, and the major vector of an emerging tick-borne disease: severe fever with thrombocytopenia syndrome (SFTS). Microbiome diversity of ticks is influenced by several factors. In this study, we investigated microbiome diversity in field-collected female and male H. longicornis ticks and compared the microbial composition of fed and unfed ticks and of those feeding on different hosts using barcode sequencing of V3-V4 region of 16S RNA gene. Regardless of sex, host, and feeding status; the highest abundance among all samples was found for the genus Coxiella. The relative numbers of Coxiella sequences decreased with the length of the blood feeding, whereas the numbers of Staphylococcus and Corynebacterium increased gradually. The dominance of Coxiella across all samples indicates that it is an obligate symbiont of H. longicornis. Overall, higher microbiome richness was detected in male ticks than in female ticks. Fed ticks showed a more diverse microbe composition than unfed ticks, and ticks fed on goats exhibited the highest diversity. These findings of this study can serve as a basis for future studies of microbiota biology and interactions between the microbes and pathogens of H. longicornis.

Endosymbionts Alter Larva-to-Nymph Transstadial Transmission of Babesia microti in Rhipicephalus haemaphysaloides Ticks

Maternally inherited endosymbionts inhabit a variety of arthropods. Some of them can protect the arthropod host against a wide range of pathogens. However, very little is known about the association between endosymbionts and pathogen susceptibility in ticks. The present study investigated the effect of endosymbionts on larva-to-nymph transstadial transmission of Babesia microti by Rhipicephalus haemaphysaloides ticks. Engorged female ticks were injected with PBS, ciprofloxacin or kanamycin. The offspring larvae were used to infest B. microti-positive mice. Prevalence of B. microti among the nymphs in different treatment groups and its association with endosymbiont density in the larvae were analyzed. The results showed that the prevalence of B. microti in the kanamycin-treated group (63.9%, 95% confidence interval (CI): 52.8–75.0%) was higher than that in the PBS (23.6%, 95% CI: 13.8–33.4%) or ciprofloxacin-treated (25.0%, 95% CI: 15.0–35.0%) groups. This increased prevalence was associated with reduced density of Coxiella-like endosymbiont but was not related to the density of Rickettsia-like endosymbiont. No direct evidence has previously been reported about the impact of Coxiella-like endosymbiont on pathogen susceptibility in ticks. This study reveals that endosymbionts are potentially important defensive symbionts of R. haemaphysaloides which may influence the colonization or susceptibility of B. microti in the tick host.

Tissue Localization and Variation of Major Symbionts in Haemaphysalis longicornis, Rhipicephalus haemaphysaloides, and Dermacentor silvarum in China

Ticks are important disease vectors, as they transmit a variety of human and animal pathogens worldwide. Symbionts that coevolved with ticks confer crucial benefits to their host in nutrition metabolism, fecundity, and vector competence. Although over 100 tick species have been identified in China, general information on tick symbiosis is limited. Here, we visualized the tissue distribution of Coxiella sp. and Rickettsia sp. in lab-reared Haemaphysalis longicornis and Rhipicephalus haemaphysaloides by fluorescent in situ hybridization. We found that Coxiella sp. colonized exclusively the Malpighian tubules and ovaries of H. longicornis, while Rickettsia sp. additionally colonized the midgut of R. haemaphysaloides We also investigated the population structure of microbiota in Dermacentor silvarum ticks collected from Inner Mongolia, China, and found that Coxiella, Rickettsia, and Pseudomonas are the three dominant genera. No significant difference in microbiota composition was found between male and female D. silvarum ticks. We again analyzed the tissue localization of Coxiella sp. and Rickettsia sp. and found that they displayed tissue tropisms similar to those in R. haemaphysaloides, except that Rickettsia sp. colonized the nuclei of spermatids instead of ovaries in D. silvarum Altogether, our results suggest that Coxiella sp. and Rickettsia sp. are the main symbionts in the three ticks and reside primarily in midgut, Malpighian tubules, and reproductive tissues, but their tissue distribution varies in association with species and sexes.IMPORTANCE Tick-borne diseases constitute a major public health burden, as they are increasing in frequency and severity worldwide. The presence of symbionts helps ticks to metabolize nutrients, promotes fecundity, and influences pathogen infections. Increasing numbers of tick-borne pathogens have been identified in China; however, knowledge of native ticks, especially tick symbiosis, is limited. In this study, we analyze the distribution of Coxiella sp. and Rickettsia sp. in tissues of laboratory-reared Haemaphysalis longicornis and Rhipicephalus haemaphysaloides and field-collected Dermacentor silvarum We found that the localization patterns of Coxiella sp. in three Chinese tick species were similar to those of other tick species. We also found a previously undefined intracellular localization of Rickettsia sp. in tick midgut and spermatids. In addition, we demonstrate that tissue tropisms of symbionts vary between species and sexes. Our findings provide new insights into the tissue localization of symbionts in native Chinese ticks and pave the way for further understanding of their functional capabilities and symbiotic interactions with ticks.

Effects of antibiotic treatment on the fecundity of Rhipicephalus haemaphysaloides ticks

BACKGROUND

Endosymbiotic bacteria inhabit a variety of arthropods including ticks and may have multiple effects on the host's survival, reproduction or pathogen acquisition and transmission. Rhipicephalus haemaphysaloides is one of the most widely distributed tick species in China. The symbiotic bacteria composition and their impacts to R. haemaphysaloides ticks have not been studied. The present study investigated the composition of microbial community in R. haemaphysaloides ticks and then assessed the effects of endosymbionts on the host's fecundity by antibiotic treatment experiments.

METHODS

The microbial population of female and male R. haemaphysaloides ticks was analyzed using Illumina Miseq sequencing of 16S rRNA gene. Thirty engorged female ticks were then randomly divided into five groups and injected with ampicillin, ciprofloxacin, kanamycin, tetracycline, or phosphate-buffered solution (PBS), respectively. Effects of antibiotic treatments on maternal oviposition, egg hatching and density of endosymbionts were evaluated.

RESULTS

Illumina Miseq sequencing showed that Coxiella and Rickettsia were the predominant bacterial genera inhabiting R. haemaphysaloides ticks. Antibiotic treatment experiments found that kanamycin reduced the density of Coxiella-like endosymbiont (Coxiella-LE hereafter) in eggs, ciprofloxacin reduced the density of Rickettsia-like endosymbiont (Rickettsia-LE), and tetracycline had effect on both endosymbionts, while ampicillin affected neither. Meanwhile hatching rates of eggs were observed to decrease greatly in the kanamycin or tetracycline-treated group but maintained in the ampicillin or ciprofloxacin-treated group. Furthermore, the reduced hatching rates were found to be associated with density of Coxiella-LE in eggs.

CONCLUSIONS

The findings indicate that Coxiella-LE is essential for the reproduction of R. haemaphysaloides ticks, and that kanamycin can be used to study the role of Coxiella-LE on ticks.

Relative transcription of autophagy-related genes in Amblyomma sculptum and Rhipicephalus microplus ticks

Ticks endure stressful off-host periods and perform as vectors of a diversity of infectious agents, thus engaging pathways that expectedly demand for autophagy. Little is known of ticks' autophagy, a conserved eukaryotic machinery assisting in homeostasis processes that also participates in tissue-dependent metabolic functions. Here, the autophagy-related ATG4 (autophagin-1), ATG6 (beclin-1) and ATG8 (LC3) mRNAs from the human diseases vector Amblyomma sculptum and the cattle-tick Rhipicephalus microplus were identified. Comparative qPCR quantifications evidenced different transcriptional status for the ATG genes in the salivary glands (SG), ovaries and intestines of actively feeding ticks. These ATGs had increased relative transcription under nutrient-deprivation, as determined by validation tests with R. microplus embryo-derivative cells BME26 and A. sculptum SG explants incubations in HBSS. Starvation lead to 4-31.8× and ~ 60-500× increments on the ATGs mRNA loads in BME26 and A. sculptum SG explants, respectively. PI3K inhibitor 3MA treatment also affected ATGs expression in BME26. Some ATGs were more transcribed in the SGs than in the ovaries of cattle-ticks. Amblyomma sculptum/R. microplus interspecific comparisons showed that ATG4 and ATG6 were 0.18× less expressed in A. sculptum SGs, but ~ 10-100× more expressed in their ovaries when compared to R. microplus organs. ATG4 and ATG8a transcript loads were ~ 120× and ~ 40× higher, respectively, in A. sculptum intestines when compared to cattle-ticks of similar weight category. ATGs expression in A. sculptum intestines increased with tick weight, indicating Atgs contribution to intracellular blood digestion. Possible roles of the autophagy machinery and their organ-specific expression profile on vector biology are discussed.

Endosymbiont CLS-HI plays a role in reproduction and development of Haemaphysalis longicornis

Coxiella-like endosymbiont (CLS-Hl) is a primary endosymbiont of Haemaphysalis longicornis. CLS-Hl infects tick special tissues and its prevalence is 100% in ovaries and Malpighian tubules. Tetracycline was injected into females, which then fed on rabbits also treated with tetracycline. The densities of CLS-Hl were measured by semi-quantitative PCR. CLS-Hl densities in ovaries and Malpighian tubes of H. longicornis had significant effects on engorged weight, feeding time, number of eggs, oviposition period, and hatching period. These findings suggested that CLS-Hl plays a role in the reproduction and development of H. longicornis.

Microbial diversity of the Tibetan tick Haemaphysalis tibetensis (Acari: Ixodidae)

The Tibetan tick Haemaphysalis tibetensis is widely distributed in the Tibetan Plateau, and is recognized as one of the primary parasites affecting domestic and wild animals. No information is available on its microbial diversity. In the current study, the microbiomes in H. tibetensis were explored using Illumina MiSeq sequencing. Results indicate that a total of 28 phyla and 38 genera were characterized from this tick, and most of the microbes were classified in the phylum Proteobacteria. Female and male H. tibetensis harbored similar composition of the microbes, with dominant bacteria from the genus Coxiella accounting for 87.5 and 66.5% in females and males, respectively. The abundance of bacteria belonging to the genus Rickettsia in females and males was 6.9 and 23.7%, respectively. These findings may help understand the relationship between this tick and its symbiontic microorganisms.

Micropathogen Community Analysis in Hyalomma rufipes via High-Throughput Sequencing of Small RNAs

Ticks are important vectors in the transmission of a broad range of micropathogens to vertebrates, including humans. Because of the role of ticks in disease transmission, identifying and characterizing the micropathogen profiles of tick populations have become increasingly important. The objective of this study was to survey the micropathogens of Hyalomma rufipes ticks. Illumina HiSeq2000 technology was utilized to perform deep sequencing of small RNAs (sRNAs) extracted from field-collected H. rufipes ticks in Gansu Province, China. The resultant sRNA library data revealed that the surveyed tick populations produced reads that were homologous to St. Croix River Virus (SCRV) sequences. We also observed many reads that were homologous to microbial and/or pathogenic isolates, including bacteria, protozoa, and fungi. As part of this analysis, a phylogenetic tree was constructed to display the relationships among the homologous sequences that were identified. The study offered a unique opportunity to gain insight into the micropathogens of H. rufipes ticks. The effective control of arthropod vectors in the future will require knowledge of the micropathogen composition of vectors harboring infectious agents. Understanding the ecological factors that regulate vector propagation in association with the prevalence and persistence of micropathogen lineages is also imperative. These interactions may affect the evolution of micropathogen lineages, especially if the micropathogens rely on the vector or host for dispersal. The sRNA deep-sequencing approach used in this analysis provides an intuitive method to survey micropathogen prevalence in ticks and other vector species.

The Tick Microbiome: Why Non-pathogenic Microorganisms Matter in Tick Biology and Pathogen Transmission

Ticks are among the most important vectors of pathogens affecting humans and other animals worldwide. They do not only carry pathogens however, as a diverse group of commensal and symbiotic microorganisms are also present in ticks. Unlike pathogens, their biology and their effect on ticks remain largely unexplored, and are in fact often neglected. Nonetheless, they can confer multiple detrimental, neutral, or beneficial effects to their tick hosts, and can play various roles in fitness, nutritional adaptation, development, reproduction, defense against environmental stress, and immunity. Non-pathogenic microorganisms may also play a role in driving transmission of tick-borne pathogens (TBP), with many potential implications for both human and animal health. In addition, the genetic proximity of some pathogens to mutualistic symbionts hosted by ticks is evident when studying phylogenies of several bacterial genera. The best examples are found within members of the Rickettsia, Francisella, and Coxiella genera: while in medical and veterinary research these bacteria are traditionally recognized as highly virulent vertebrate pathogens, it is now clear to evolutionary ecologists that many (if not most) Coxiella, Francisella, and Rickettsia bacteria are actually non-pathogenic microorganisms exhibiting alternative lifestyles as mutualistic ticks symbionts. Consequently, ticks represent a compelling yet challenging system in which to study microbiomes and microbial interactions, and to investigate the composition, functional, and ecological implications of bacterial communities. Ultimately, deciphering the relationships between tick microorganisms as well as tick symbiont interactions will garner invaluable information, which may aid in the future development of arthropod pest and vector-borne pathogen transmission control strategies.

Symbiont dynamics of the Tibetan tick Haemaphysalis tibetensis (Acari: Ixodidae)

Background

Characterization of the microbial diversity and symbiont dynamics of ticks may help to understand the development of ticks and reveal new strategies to control tick-transmitted pathogens, which has not yet been explored in the Tibetan tick Haemaphysalis tibetensis. This tick species is widely distributed in the Tibetan Plateau, and is recognized as one of the primary parasites affecting domestic and wild animals.

Methods

In the present study, the endosymbionts of H. tibetensis were characterized using diagnostic polymerase chain reaction (diagnostic PCR), and further evaluated for tissue distribution and population dynamics at each developmental stage of ticks and in tissues at different reproductive statuses by real-time quantitative polymerase chain reaction (RT-qPCR).

Results

Two symbionts were found in H. tibetensis, and named as CLS-Ht (Coxiella-like symbiont in H. tibetensis) and RLS-Ht (Rickettsia-like symbiont in H. tibetensis). They showed 100% infection rate in both females and males of H. tibetensis. CLS-Ht and RLS-Ht can be observed within eggs, larvae, nymphs and adults, which indicates vertical transmission in H. tibetensis. CLS-Ht was specifically distributed in the female ovaries and Malpighian tubules, whereas RLS-Ht was detected within ovaries, Malpighian tubules, salivary glands and midguts of the ticks. Real-time qPCR suggested that adult ticks carried the largest amount of CLS-Ht and RLS-Ht with CLS-Ht having a significantly higher presence in females than in males (P < 0.05), whereas the presence of RLS-Ht showed no significant differences between sexes. In the ovaries, CLS-Ht distribution reached a peak at one day post-engorgement, and then gradually declined to a lower level, whereas no change was observed in RLS-Ht. In Malpighian tubules, the amount of both symbionts displayed an increasing trend with time post-engorgement. In midguts and salivary glands, the amount of RLS-Ht showed no significant differences.

Conclusion

Two novel endosymbionts (CLS-Ht and RLS-Ht) were characterized in H. tibetensis both showing a high prevalence and stable vertical transmission. The described tissue distribution and population dynamics might imply the important functions of these symbionts during the development and reproduction of ticks.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-017-2199-0) contains supplementary material, which is available to authorized users.

Tick-Pathogen Interactions and Vector Competence: Identification of Molecular Drivers for Tick-Borne Diseases

Ticks and the pathogens they transmit constitute a growing burden for human and animal health worldwide. Vector competence is a component of vectorial capacity and depends on genetic determinants affecting the ability of a vector to transmit a pathogen. These determinants affect traits such as tick-host-pathogen and susceptibility to pathogen infection. Therefore, the elucidation of the mechanisms involved in tick-pathogen interactions that affect vector competence is essential for the identification of molecular drivers for tick-borne diseases. In this review, we provide a comprehensive overview of tick-pathogen molecular interactions for bacteria, viruses, and protozoa affecting human and animal health. Additionally, the impact of tick microbiome on these interactions was considered. Results show that different pathogens evolved similar strategies such as manipulation of the immune response to infect vectors and facilitate multiplication and transmission. Furthermore, some of these strategies may be used by pathogens to infect both tick and mammalian hosts. Identification of interactions that promote tick survival, spread, and pathogen transmission provides the opportunity to disrupt these interactions and lead to a reduction in tick burden and the prevalence of tick-borne diseases. Targeting some of the similar mechanisms used by the pathogens for infection and transmission by ticks may assist in development of preventative strategies against multiple tick-borne diseases.

Proteases of haematophagous arthropod vectors are involved in blood-feeding, yolk formation and immunity - a review

Ticks, triatomines, mosquitoes and sand flies comprise a large number of haematophagous arthropods considered vectors of human infectious diseases. While consuming blood to obtain the nutrients necessary to carry on life functions, these insects can transmit pathogenic microorganisms to the vertebrate host. Among the molecules related to the blood-feeding habit, proteases play an essential role. In this review, we provide a panorama of proteases from arthropod vectors involved in haematophagy, in digestion, in egg development and in immunity. As these molecules act in central biological processes, proteases from haematophagous vectors of infectious diseases may influence vector competence to transmit pathogens to their prey, and thus could be valuable targets for vectorial control.

Identification, Distribution and Population Dynamics of Francisella-like Endosymbiont in Haemaphysalis doenitzi (Acari: Ixodidae)

Francisella-like endosymbionts (FLEs) with significant homology to Francisella tularensis (γ-proteobacteria) have been characterized in several tick species, whereas knowledge on their distribution and population dynamics in ticks remains meager. Hence, in the current study, we identified a novel Francisella-like endosymbiont (FLEs-Hd) from the tick Haemaphysalis doenitzi and evaluated the putative functions of this symbiont. Results indicated that FLEs-Hd had 100% infection rate and a perfect vertical transmission in H. doenitzi, and that it is distributed in ovaries, malpighian tubules, salivary glands and midguts of the ticks, suggesting that FLEs-Hd presumably is a crucial symbiont of the host without specific tissue tropism. To further explore the function of the symbiont, the population dynamics of FLEs-Hd at each developmental stage of ticks and in tissues at different reproductive statuses were determined by real-time quantitative polymerase chain reaction (real-time qPCR). Results showed that the high density and regular population dynamics of FLEs-Hd appeared in female ovaries, suggesting that the symbiont may provide necessary nutrients or regulators to ensure normal ovary development of ticks.

Bacterial community in Haemaphysalis ticks of domesticated animals from the Orang Asli communities in Malaysia

Ticks are vectors in the transmission of many important infectious diseases in human and animals. Ticks can be readily found in the semi-forested areas such as the settlements of the indigenous people in Malaysia, the Orang Asli. There is still minimal information available on the bacterial agents associated with ticks found in Malaysia. We performed a survey of the bacterial communities associated with ticks collected from domestic animals found in two Orang Asli villages in Malaysia. We collected 62 ticks, microscopically and molecularly identified as related to Haemaphysalis wellingtoni, Haemaphysalis hystricis and Haemaphysalis bispinosa. Bacterial 16s rRNA hypervariable region (V6) amplicon libraries prepared from the tick samples were sequenced on the Ion Torrent PGM platform. We detected a total of 392 possible bacterial genera after pooling and sequencing 20 samples, indicating a diverse bacterial community profile. Dominant taxa include the potential tick endosymbiont, Coxiella. Other dominant taxa include the tick-associated pathogen, Rickettsia, and environmental bacteria such as Bacillus, Mycobacterium, Sphingomonas and Pseudomonas. Other known tick-associated bacteria were also detected, including Anaplasma, Ehrlichia, Rickettsiella and Wolbachia, albeit at very low abundance. Specific PCR was performed on selected samples to identify Rickettsia and Coxiella. Sequence of Rickettsia felis, which causes spotted fever in human and cats, was identified in one sample. Coxiella endosymbionts were detected in three samples. This study provides the baseline knowledge of the microbiome of ticks in Malaysia, focusing on tick-associated bacteria affecting the Orang Asli communities. The role of the herein found Coxiella and Rickettsia in tick physiology or disease transmission merits further investigation.

Arsenophonus nasoniae and Rickettsiae Infection of Ixodes ricinus Due to Parasitic Wasp Ixodiphagus hookeri

Arsenophonus nasoniae, a male-killing endosymbiont of chalcid wasps, was recently detected in several hard tick species. Following the hypothesis that its presence in ticks may not be linked to the direct occurrence of bacteria in tick's organs, we identified A. nasoniae in wasps emerging from parasitised nymphs. We confirmed that 28.1% of Ixodiphagus hookeri wasps parasitizing Ixodes ricinus ticks were infected by A. nasoniae. Moreover, in examined I. ricinus nymphs, A. nasoniae was detected only in those, which were parasitized by the wasp. However, in part of the adult wasps as well as in some ticks that contained wasp's DNA, we did not confirm A. nasoniae. We also found, that in spite of reported male-killing, some newly emerged adult wasp males were also infected by A. nasoniae. Additionally, we amplified the DNA of Rickettsia helvetica and Rickettsia monacensis (known to be Ixodes ricinus-associated bacteria) in adult parasitoid wasps. This may be related either with the digested bacterial DNA in wasp body lumen or with a role of wasps in circulation of rickettsiae among tick vectors.

Ticks and tick-borne novel bunyavirus collected from the natural environment and domestic animals in Jinan city, East China

Since 2011, 73 cases of the severe fever with thrombocytopenia syndrome, a novel tick-borne disease, have been reported in Jinan city through information system for disease control and prevention. Therefore, this study aimed to investigate the species, distribution, host animals of ticks and tick-borne pathogens. A total of 722 ticks were collected from two types of natural environment and six kinds of domestic animal in Jinan city. All the sampled ticks belonged to the same species, namely Haemaphysalis longicornis, and 94.7% of them were adult. The density of free-living ticks in grassland was nearly six times that in shrub. The prevalence of the goat (53.3%) was highest among the domestic animals. The host body region most frequently parasitized by H. longicornis was the head (77.8%), especially ears and periocular region. Novel bunyavirus was detected on the free-ranging goats in Jinan city. Acaricide treatment with a higher concentration on the ears, periocular region and the groin of domestic animals should be recommended to control the ticks effectively.

"Candidatus Fokinia solitaria", a Novel "Stand-Alone" Symbiotic Lineage of Midichloriaceae (Rickettsiales)

Recently, the family Midichloriaceae has been described within the bacterial order Rickettsiales. It includes a variety of bacterial endosymbionts detected in different metazoan host species belonging to Placozoa, Cnidaria, Arthropoda and Vertebrata. Representatives of Midichloriaceae are also considered possible etiological agents of certain animal diseases. Midichloriaceae have been found also in protists like ciliates and amoebae. The present work describes a new bacterial endosymbiont, "Candidatus Fokinia solitaria", retrieved from three different strains of a novel Paramecium species isolated from a wastewater treatment plant in Rio de Janeiro (Brazil). Symbionts were characterized through the full-cycle rRNA approach: SSU rRNA gene sequencing and fluorescence in situ hybridization (FISH) with three species-specific oligonucleotide probes. In electron micrographs, the tiny rod-shaped endosymbionts (1.2 x 0.25-0.35 μm in size) were not surrounded by a symbiontophorous vacuole and were located in the peripheral host cytoplasm, stratified in the host cortex in between the trichocysts or just below them. Frequently, they occurred inside autolysosomes. Phylogenetic analyses of Midichloriaceae apparently show different evolutionary pathways within the family. Some genera, such as "Ca. Midichloria" and "Ca. Lariskella", have been retrieved frequently and independently in different hosts and environmental surveys. On the contrary, others, such as Lyticum, "Ca. Anadelfobacter", "Ca. Defluviella" and the presently described "Ca. Fokinia solitaria", have been found only occasionally and associated to specific host species. These last are the only representatives in their own branches thus far. Present data do not allow to infer whether these genera, which we named "stand-alone lineages", are an indication of poorly sampled organisms, thus underrepresented in GenBank, or represent fast evolving, highly adapted evolutionary lineages.

Coxiella-like endosymbiont associated to the "Anatolian brown tick" Rhipicephalus bursa in Southern Italy

Several different ticks have been reported to harbor microbes related to Coxiella burnetii, the agent of the Q fever. Rhipicephalus bursa is an important vector of tick-borne diseases in livestock in Mediterranean area; it is also abundant in ovi-caprine farms with C. burnetii infection, in Southern Italy. 60 females of Rh. bursa (15 pools) and 40 their eggs (2 pools) were screened for C. burnetii by a conventional PCR targeting the insertion sequence IS1111 and by Loop mediated isothermal amplification assay (LAMP) targeting com1 gene. One of 15 tick pools (1/15) and both egg pools (2/2) were found positive by LAMP assay and negative by PCR targeting IS1111 gene. 16S rRNA gene was amplified by PCR from the LAMP-positive pools, amplicons were sequenced and found 95% similar to the corresponding sequences from C. burnetii. This let us to hypothesize the presence of a new Coxiella-like endosymbiont associated with Rh. bursa which could be vertically transmitted, described here for the first time. The lack of detection of IS1111 in Coxiella endosymbiont of Rh. bursa could be related to the possible absence of the Pathogenicity island of C. burnetii, to which IS1111s are associated.

Assessment of four DNA fragments (COI, 16S rDNA, ITS2, 12S rDNA) for species identification of the Ixodida (Acari: Ixodida)

Background

The 5’ region of cytochrome oxidase I (COI) is the standard marker for DNA barcoding. However, COI has proved to be of limited use in identifying some species, and for some taxa, the coding sequence is not efficiently amplified by PCR. These deficiencies lead to uncertainty as to whether COI is the most suitable barcoding fragment for species identification of ticks.

Methods

In this study, we directly compared the relative effectiveness of COI, 16S ribosomal DNA (rDNA), nuclear ribosomal internal transcribed spacer 2 (ITS2) and 12S rDNA for tick species identification. A total of 307 sequences from 84 specimens representing eight tick species were acquired by PCR. Besides the 1,834 published sequences of 189 tick species from GenBank and the Barcode of Life Database, 430 unpublished sequences representing 59 tick species were also successfully screened by Bayesian analyses. Thereafter, the performance of the four DNA markers to identify tick species was evaluated by identification success rates given by these markers using nearest neighbour (NN), BLASTn, liberal tree-based or liberal tree-based (+threshold) methods.

Results

Genetic divergence analyses showed that the intra-specific divergence of each marker was much lower than the inter-specific divergence. Our results indicated that the rates of correct sequence identification for all four markers (COI, 16S rDNA, ITS2, 12S rDNA) were very high (> 96%) when using the NN methodology. We also found that COI was not significantly better than the other markers in terms of its rate of correct sequence identification. Overall, BLASTn and NN methods produced higher rates of correct species identification than that produced by the liberal tree-based methods (+threshold or otherwise).

Conclusions

As the standard DNA barcode, COI should be the first choice for tick species identification, while 16S rDNA, ITS2, and 12S rDNA could be used when COI does not produce reliable results. Besides, NN and BLASTn are efficient methods for species identification of ticks.