SciCombinator

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Concept: Ixodidae

168

BACKGROUND: Candidatus Neoehrlichia mikurensis (CNM) has been described in the hard tick Ixodes ricinus and rodents as well as in some severe cases of human disease. The aims of this study were to identify DNA of CNM in small mammals, the ticks parasitizing them and questing ticks in areas with sympatric existence of Ixodes ricinus and Dermacentor reticulatus in Germany. METHODS: Blood, transudate and organ samples (spleen, kidney, liver, skin) of 91 small mammals and host-attached ticks from altogether 50 small mammals as well as questing I. ricinus ticks (n=782) were screened with a real-time PCR for DNA of CNM. RESULTS: 52.7% of the small mammals were positive for CNM-DNA. The majority of the infected animals were yellow-necked mice (Apodemus flavicollis) and bank voles (Myodes glareolus). Small mammals with tick infestation were more often infected with CNM than small mammals without ticks. Compared with the prevalence of ~25% in the questing I. ricinus ticks, twice the prevalence in the rodents provides evidence for their role as reservoir hosts for CNM. CONCLUSION: The high prevalence of this pathogen in the investigated areas in both rodents and ticks points towards the need for more specific investigation on its role as a human pathogen.

Concepts: Lyme disease, Mammal, Rodent, Ixodidae, Acari, Ixodes scapularis, Dermacentor variabilis, Ixodes holocyclus

167

BACKGROUND: Genomic resources within the phylum Arthropoda are largely limited to the true insects but are beginning to include unexplored subphyla, such as the Crustacea and Chelicerata. Investigations of these understudied taxa uncover high frequencies of orphan genes, which lack detectable sequence homology to genes in pre-existing databases. The ticks (Acari: Chelicerata) are one such understudied taxon for which genomic resources are urgently needed. Ticks are obligate blood-feeders that vector major diseases of humans, domesticated animals, and wildlife. In analyzing a transcriptome of the lone star tick Amblyomma americanum, one of the most abundant disease vectors in the United States, we find a high representation of unannotated sequences. We apply a general framework for quantifying the origin and true representation of unannotated sequences in a dataset and for evaluating the biological significance of orphan genes. RESULTS: Expressed sequence tags (ESTs) were derived from different life stages and populations of A. americanum and combined with ESTs available from GenBank to produce 14,310 ESTs, over twice the number previously available. The vast majority (71%) has no sequence homology to proteins archived in UniProtKB. We show that poor sequence or assembly quality is not a major contributor to this high representation by orphan genes. Moreover, most unannotated sequences are functional: a microarray experiment demonstrates that 59% of functional ESTs are unannotated. Lastly, we attempt to further annotate our EST dataset using genomic datasets from other members of the Acari, including Ixodes scapularis, four other tick species and the mite Tetranychus urticae. We find low homology with these species, consistent with significant divergence within this subclass. CONCLUSIONS: We conclude that the abundance of orphan genes in A. americanum likely results from 1) taxonomic isolation stemming from divergence within the tick lineage and limited genomic resources for ticks and 2) lineage-specific genes needing functional genomic studies to evaluate their association with the unique biology of ticks. The EST sequences described here will contribute substantially to the development of tick genomics. Moreover, the framework provided for the evaluation of orphan genes can guide analyses of future transcriptome sequencing projects.

Concepts: DNA, Genomics, Lyme disease, Tick, Ixodidae, Acari, Arachnid, Amblyomma americanum

35

Bourbon virus (BRBV) was first isolated in 2014 from a resident of Bourbon County, Kansas, USA, who died of the infection. In 2015, an ill Payne County, Oklahoma, resident tested positive for antibodies to BRBV, before fully recovering. We retrospectively tested for BRBV in 39,096 ticks from northwestern Missouri, located 240 km from Bourbon County, Kansas. We detected BRBV in 3 pools of Amblyomma americanum (L.) ticks: 1 pool of male adults and 2 pools of nymphs. Detection of BRBV in A. americanum, a species that is aggressive, feeds on humans, and is abundant in Kansas and Oklahoma, supports the premise that A. americanum is a vector of BRBV to humans. BRBV has not been detected in nonhuman vertebrates, and its natural history remains largely unknown.

Concepts: U.S. state, Ixodidae, Native Americans in the United States, Democratic Party, Amblyomma americanum, Kansas, Missouri, Oklahoma

34

Chemokines function via G-protein coupled receptors in a robust network to recruit immune cells to sites of inflammation. Due to the complexity of this network, targeting single chemokines or receptors has not been successful in inflammatory disease. Dog tick saliva contains polyvalent CC-chemokine binding peptides termed evasins 1 and 4, that efficiently disrupt the chemokine network in models of inflammatory disease. Here we develop yeast surface display as a tool for functionally identifying evasins, and use it to identify 10 novel polyvalent CC-chemokine binding evasin-like peptides from salivary transcriptomes of eight tick species in Rhipicephalus and Amblyomma genera. These evasins have unique binding profiles compared to evasins 1 and 4, targeting CCL2 and CCL13 in addition to other CC-chemokines. Evasin binding leads to neutralisation of chemokine function including that of complex chemokine mixtures, suggesting therapeutic efficacy in inflammatory disease. We propose that yeast surface display is a powerful approach to mine potential therapeutics from inter-species protein interactions that have arisen during evolution of parasitism in ticks.

Concepts: Immune system, Inflammation, Protein, Signal transduction, Chemokine, G protein-coupled receptor, Tick, Ixodidae

28

Abstract :  Theilerioses and babesioses are important diseases in Iranian sheep. The present study was undertaken to identify and classify/specify Theileria spp. and Babesia spp. in sheep and vector ticks. Investigation was carried out from 2009 to 2011 in the Khorasan Razavi Province, Iran. In total, 302 sheep originating from 60 different flocks were clinically examined and their blood collected. In addition, from the same flocks, ixodid ticks were sampled. Stained blood smears were microscopically examined for the presence of Theileria and Babesia organisms, and a semi-nested PCR was used for subsequent molecular specification. From the ticks, salivary glands and uterus were isolated and subsequently analyzed by semi-nested PCR. Piroplasm organisms were observed in 29% of the blood smears with low parasitemia, whereas 65% of the blood samples yielded positive PCR findings. The presence of Theileria ovis (55.6%), Theileria lestoquardi, and mixed infection with Theileria spp. and Babesia ovis were detected by semi-nested PCR in 0.3%, 5.6%, and 0.99%, respectively. In total, 429 ixodid ticks were collected from different areas of the province. The most prevalent ticks were Rhipicephalus turanicus (n = 376; 87.6% of the total), followed by Hyalomma marginatum turanicum (n = 30; 7.0%), Dermacentor raskemensis (n = 12; 2.8%), Hyalomma anatolicum anatolicum (n = 7; 1.6%), Dermacentor marginatus (n = 2; 0.5%), Rhipicephalus bursa (n = 1; 0.2%), and Haemaphysalis sp. (n = 1; 0.2%). Of the positive R. turanicus samples, 5 (5.7%) were infected with T. ovis and 2 (2.9%) with T. lestoquardi. Neither Babesia ovis nor Babesia motasi infection was detected in salivary glands or uterine samples of the ticks. The results also suggest that R. turanicus could be the vector responsible for transmission of the 2 Theileria species.

Concepts: Lyme disease, Tick, Ixodidae, Acari, Babesiosis, Glands, Theileria, Piroplasmida

27

In the early 1980s, Ixodes spp. ticks were implicated as the key North American vectors of Borrelia burgdorferi (Johnson, Schmid, Hyde, Steigerwalt and Brenner) (Spirocheatales: Spirochaetaceae), the etiological agent of Lyme disease. Concurrently, other human-biting tick species were investigated as potential B. burgdorferi vectors. Rashes thought to be erythema migrans were observed in patients bitten by Amblyomma americanum (L.) (Acari: Ixodidae) ticks, and spirochetes were visualized in a small percentage of A. americanum using fluorescent antibody staining methods, sparking interest in this species as a candidate vector of B. burgdorferi. Using molecular methods, the spirochetes were subsequently described as Borrelia lonestari sp. nov. (Spirocheatales: Spirochaetaceae), a transovarially transmitted relapsing fever Borrelia of uncertain clinical significance. In total, 54 surveys from more than 35 research groups, involving more than 52,000 ticks, have revealed a low prevalence of B. lonestari, and scarce B. burgdorferi, in A. americanum. In Lyme disease-endemic areas, A. americanum commonly feeds on B. burgdorferi-infected hosts; the extremely low prevalence of B. burgdorferi in this tick results from a saliva barrier to acquiring infection from infected hosts. At least nine transmission experiments involving B. burgdorferi in A. americanum have failed to demonstrate vector competency. Advancements in molecular analysis strongly suggest that initial reports of B. burgdorferi in A. americanum across many states were misidentified B. lonestari, or DNA contamination, yet the early reports continue to be cited without regard to the later clarifying studies. In this article, the surveillance and vector competency studies of B. burgdorferi in A. americanum are reviewed, and we conclude that A. americanum is not a vector of B. burgdorferi.

Concepts: Bacteria, Lyme disease, Tick, Ixodidae, Borrelia burgdorferi, Borrelia, Spirochaetes, Amblyomma americanum

27

Detection of resistance levels against cypermethrin and deltamethrin, the most commonly used synthetic pyrethroids (SPs) against Rhipicephalus (Boophilus) microplus collected from Moga, Punjab (India) was carried out using larval packet test. Results indicated the presence of resistance of level I and III against cypermethrin (resistance factors (RF) = 4.67) and deltamethrin (RF = 34.2), respectively. Adult immersion test was used to assess the acaricidal activity of aqueous and ethanolic extracts of leaves of Cymbopogon winterianus, Vitex negundo, and Withania somnifera along with roots of V. negundo against the SP resistant engorged females of R. (B.) microplus. The efficacy of various extracts was assessed by estimation of percent adult mortality, reproductive index (RI), percent inhibition of oviposition (%IO), and hatching rate. A concentration dependent increase in tick mortality was recorded which was more marked with various ethanolic extracts, and highest mortality was recorded in ticks treated with ethanolic extract of leaves of C. winterianus. The LC50 values were determined by applying regression equation analysis to the probit transformed data of mortality for various aqueous and ethanolic extracts. Acaricidal property was recorded to be higher in ethanolic extracts, and high activity was found with the ethanolic extract of leaves of C. winterianus with LC50 (95 % CL) values of 0.46 % (0.35-0.59 %), followed by W. somnifera as 5.21 % (4.45-6.09 %) and V. negundo as 7.02 % (4.58-10.74 %). The egg mass weight of the live ticks treated with different concentrations of the various extract was significantly (p < 0.01) lower than that of control ticks; consequently, the RI and the %IO value of the treated ticks were reduced. Further, complete inhibition of hatching was recorded in eggs laid by ticks treated with ethanolic extracts of leaves of V. negundo and aqueous extracts of leaves of W. somnifera. The results of the current study indicate that extracts of C. winterianus, V. negundo, and W. somnifera can be used for the control of SP resistant ticks.

Concepts: Concentration, Ixodidae, Acari, Pyrethroid, Extract, Withania somnifera, Cymbopogon, Vitex negundo

26

Heartland virus (HRTV), the first pathogenic Phlebovirus (Family: Bunyaviridae) discovered in the United States, was recently described from two Missouri farmers. In 2012, we collected 56,428 ticks representing three species at 12 sites including both patients' farms. Amblyomma americanum and Dermacentor variabilis accounted for nearly all ticks collected. Ten pools composed of deplete nymphs of A. americanum collected at a patient farm and a nearby conservation area were reverse transcription-polymerase chain reaction positive, and eight pools yielded viable viruses. Sequence data from the nonstructural protein of the Small segment indicates that tick strains and human strains are very similar, ≥ 97.6% sequence identity. This is the first study to isolate HRTV from field-collected arthropods and to implicate ticks as potential vectors. Amblyomma americanum likely becomes infected by feeding on viremic hosts during the larval stage, and transmission to humans occurs during the spring and early summer when nymphs are abundant and actively host seeking.

Concepts: Protein, Lyme disease, Viruses, Tick, Ixodidae, Acari, Amblyomma americanum, Dermacentor variabilis

24

Arthropods are dangerous vectors of agents of deadly diseases, which may hit as epidemics or pandemics in the increasing world population of humans and animals. Among them, ticks transmit more pathogen species than any other group of blood-feeding arthropods worldwide. Thus, the effective and eco-friendly control of tick vectors in a constantly changing environment is a crucial challenge. A number of novel routes have been attempted to prevent and control tick-borne diseases, including the development of (i) vaccines against viruses vectored by ticks; (ii) pheromone-based control tools, with special reference to the “lure and kill” techniques; (iii) biological control programmes relying on ticks' natural enemies and pathogens; and (iv) the integrated pest management practices aimed at reducing tick interactions with livestock. However, the extensive employment of acaricides and tick repellents still remains the two most effective and ready-to-use strategies. Unfortunately, the first one is limited by the rapid development of resistance in ticks, as well as by serious environmental concerns. On the other hand, the exploitation of plants as sources of effective tick repellents is often promising. Here, we reviewed current knowledge concerning the effectiveness of plant extracts as acaricides or repellents against tick vectors of public health importance, with special reference to Ixodes ricinus, Ixodes persulcatus, Amblyomma cajennense, Haemaphysalis bispinosa, Haemaphysalis longicornis, Hyalomma anatolicum, Hyalomma marginatum rufipes, Rhipicephalus appendiculatus, Rhipicephalus (Boophilus) microplus, Rhipicephalus pulchellus, Rhipicephalus sanguineus and Rhipicephalus turanicus. Eighty-three plant species from 35 botanical families were selected. The most frequent botanical families exploited as sources of acaricides and repellents against ticks were Asteraceae (15 % of the selected studies), Fabaceae (9 %), Lamiaceae (10 %), Meliaceae (5 %), Solanaceae (6 %) and Verbenaceae (5 %). Regression equation analyses showed that the literature grew by approximately 20 % per year (period: 2005-2015). Lastly, in the final section, insights for future research are discussed. We focused on some caveats for future data collection and analysis. Current critical points mainly deal with (a) not uniform methods used, which prevent proper comparison of the results; (b) inaccurate tested concentrations, frequently 100 % concentration corresponded to the gross extract, where the exact amounts of extracted substances are unknown; and © not homogeneous size of tested tick instars and species. Overall, the knowledge summarized in this review may be helpful for comparative screening among extensive numbers of plant-borne preparations, in order to develop newer and safer tick control tools.

Concepts: Lyme disease, Tick, Ixodidae, Acari, Ixodes scapularis, Rhipicephalus sanguineus, Rhipicephalus, Amblyomma

15

Juvenile hormone (JH) controls the growth, development, metamorphosis, and reproduction of insects. For many years, the general assumption has been that JH regulates tick and other acarine development and reproduction the same as in insects. Although researchers have not been able to find the common insect JHs in hard and soft tick species and JH applications appear to have no effect on tick development, it is difficult to prove the negative or to determine whether precursors to JH are made in ticks. The tick synganglion contains regions which are homologous to the corpora allata, the biosynthetic source for JH in insects. Next-gen sequencing of the tick synganglion transcriptome was conducted separately in adults of the American dog tick, Dermacentor variabilis, the deer tick, Ixodes scapularis, and the relapsing fever tick, Ornithodoros turicata as a new approach to determine whether ticks can make JH or a JH precursor. All of the enzymes that make up the mevalonate pathway from acetyl-CoA to farnesyl diphosphate (acetoacetyl-CoA thiolase, HMG-S, HMG-R, mevalonate kinase, phosphomevalonate kinase, diphosphomevalonate decarboxylase, and farnesyl diphosphate synthase) were found in at least one of the ticks studied but most were found in all three species. Sequence analysis of the last enzyme in the mevalonate pathway, farnesyl diphosphate synthase, demonstrated conservation of the seven prenyltransferase regions and the aspartate rich motifs within those regions typical of this enzyme. In the JH branch from farnesyl diphosphate to JH III, we found a putative farnesol oxidase used for the conversion of farnesol to farnesal in the synganglion transcriptome of I. scapularis and D. variabilis. Methyltransferases (MTs) that add a methyl group to farnesoic acid to make methyl farnesoate were present in all of the ticks studied with similarities as high as 36% at the amino acid level to insect JH acid methyltransferase (JHAMT). However, when the tick MTs were compared to the known insect JHAMTs from several insect species at the amino acid level, the former lacked the farnesoic acid binding motif typical in insects. The P450s shown in insects to add the C10,11 epoxide to methyl farnesoate, are in the CYP15 family; this family was absent in our tick transcriptomes and in the I. scapularis genome, the only tick genome available. These data suggest that ticks do not synthesize JH III but have the mevalonate pathway and may produce a JH III precursor.

Concepts: Lyme disease, Tick, Ixodidae, Acari, Ixodes scapularis, Babesiosis, Dermacentor variabilis