Acetylcholinesterases of blood-feeding flies and ticks

Effects of Piper aduncum (Piperales: Piperaceae) Essential Oil and Its Main Component Dillapiole on Detoxifying Enzymes and Acetylcholinesterase Activity of Amblyomma sculptum (Acari: Ixodidae)

Amblyomma sculptum is a species of tick in the family Ixodidae, with equids and capybaras among its preferred hosts. In this study, the acaricidal activity of the essential oil (EO) from Piper aduncum and its main component, Dillapiole, were evaluated against larvae of A. sculptum to establish lethal concentration values and assess the effects of these compounds on tick enzymes. Dillapiole exhibited slightly greater activity (LC50 = 3.38 mg/mL; 95% CI = 3.24 to 3.54) than P. aduncum EO (LC50 = 3.49 mg/mL; 95% CI = 3.36 to 3.62) against ticks. The activities of α-esterase (α-EST), β-esterase (β-EST), and glutathione-S-transferase (GST) enzymes in A. sculptum larvae treated with Dillapiole showed a significant increase compared to the control at all concentrations (LC5, LC25, LC50 and LC75), similar results were obtained with P. aduncum EO, except for α-EST, which did not differ from the control at the highest concentration (LC75). The results of the acetylcholinesterase (AChE) activity show an increase in enzyme activity at the two lower concentrations (LC5 and LC25) and a reduction in activity at the two higher, lethal concentrations (LC50 and LC75) compared to the control. These results suggest potential mechanisms of action for these natural acaricides and can provide guidance for the future development of potential plant-derived formulations.

In vitro acaricidal activity of essential oils and their binary mixtures against ixodes scapularis (Acari: Ixodidae)

Ixodes scapularis ticks are vectors of infectious agents that cause illness in humans, including Lyme disease. Recent years have seen a surge in tick-borne diseases (TBD) resulting in a high demand for tick management products. Plants offer a valuable source of active compounds for the development of novel, eco-friendly tick control products, reducing potential risks to human and animal health. Essential oils (EOs) have emerged as potential acaricides and repellents against ticks providing an alternative to synthetic chemicals and aiding in the prevention of TBD by lowering the risk of tick bites. We investigated the acaricidal activity of EOs from lemongrass (Cymbopogon citratus), geranium (Pelargonium x asperum), savory thyme (Thymus saturejoides), and white thyme (Thymus zygis) on I. scapularis. The interactions (i.e., synergistic, antagonistic, or additive) of their binary mixtures were also evaluated. EO samples were analyzed via gas chromatography-mass spectrometry to determine their chemical composition. The adult immersion test was used to determine the lethal concentration (LC50) of each EO alone and in mixtures. Quantitative assessment of synergistic, additive, or antagonistic effect of the binary mixtures was performed by calculating the combination index. Strong acaricidal activity was recorded for savory thyme and white thyme EOs, with LC50 values of 28.0 and 11.0 μg/μL, respectively. The LC50 of lemongrass and geranium EOs were 49.0 and 39.7 μg/μL, respectively. Among the tested EOs, savory thyme and white thyme had a strong acaricidal effect on I. scapularis, which might be linked to the presence of carvacrol (26.05 % ± 0.38) and thymol (53.6 % ± 2.31), main components present in savory thyme and white thyme EOs, respectively. The tick killing efficacy of lemongrass and geranium EOs was lower when mixed than when used separately (LC50 of 65.3 µg/µL). The same happened with savory thyme and white thyme EOs, except at 9.75 µg/µL where they had a synergistic effect (LC50 of 58.3 µg/µL). Lemongrass and savory thyme EOs had a synergistic effect at low concentrations, and an antagonistic effect at higher concentrations (LC50 of 95.4 µg/µL). Lemongrass and white thyme EOs had a synergistic effect against ticks from 15 to 120 µg/µL (LC50 of 18.5 µg/µL) similar to white thyme EO. Geranium and savory thyme EOs had an antagonistic effect at all concentrations, with an LC50 of 66.8 µg/µL. Geranium and white thyme EOs also had an antagonistic effect, except at 12.7 µg/µL where they had a synergistic effect (LC50 of 66.8 µg/µL). The interaction observed when combining selected essential oils suggests promising potential for developing acaricidal formulations aimed at controlling ticks and curbing the transmission of tick-borne disease agents.

The Use of Cannabis sativa L. for Pest Control: From the Ethnobotanical Knowledge to a Systematic Review of Experimental Studies

Background: Despite the benefits that synthetic pesticides have provided in terms of pest and disease control, they cause serious long-term consequences for both the environment and living organisms. Interest in eco-friendly products has subsequently increased in recent years. Methods: This article briefly analyzes the available ethnobotanical evidence regarding the use of Cannabis sativa as a pesticide and offers a systematic review of experimental studies. Results: Our findings indicate that both ethnobotanical and experimental procedures support the use of C. sativa as a pesticide, as remarkable toxicity has been observed against pest organisms. The results included in the systematic review of experimental studies (n=30) show a high degree of heterogeneity, but certain conclusions can be extracted to guide further research. For instance, promising pesticide properties were reported for most of the groups of species tested, especially Arachnida and Insecta; the efficacy of C. sativa as a pesticide can be derived from a wide variety of compounds that it contains and possible synergistic effects; it is crucial to standardize the phytochemical profile of C. sativa plants used as well as to obtain easily reproducible results; appropriate extraction methods should be explored; and upper inflorescences of the plant may be preferred for the production of the essential oil, but further studies should explore better other parts of the plant. Conclusion: In the coming years, as new findings are produced, the promising potential of C. sativa as a pesticide will be elucidated, and reviews such as the present one constitute useful basic tools to make these processes easier.

In Silico Approaches to Develop Herbal Acaricides Against R. (Boophilus)Microplus And In Vitro Anti-Tick Activities of Selected Medicinal Plants

In tropical and sub-tropical areas of the world the most damaging pest of the livestock sector are cattle tick, Rhipicephalus microplus. The current study was aimed to generate phytochemical derived acaricides to control Rhipicephalus microplus populations, to maintain livestock herd production, minimize economic losses and to reduce uses of man-made chemicals acaricides. To achieve this goal, Adult immersion and larval package test were used to determine the feasibility of Berberium lyceum and Tamarixa aphylla against Rhipicephalus microplus ticks. Further, an In silico technique was employed to discover biologically active substances from both plants using docking method. Berberium lyceum and Tamarixa aphylla exhibited a reasonably high fatal effect at 40.0 mg/L on egg laying (index of egg laying = 0.19 and 0.19) respectively, thus inhibiting the oviposition (49.5 and 45.1, respectively) and the larval mortality (97% and 93%, respectively). Further, we also used Chem-Draw ultra-software (v. 12.0.2.1076. 2010) to illustrate different structures of38 known bioactive phytochemicals which are discovered in the PubChem database and verify the hypothesis that tick inhibition was linked to acetylcholinesterase (AChE). Barbamunine and rutin from Berberium lyceum showed remarkable interaction with RmAChE1 active site residues with docking scores of −9.11 to −8.71 while phytol and dehydrodigallic acid from Tamarix aphylla showed comparable docking scores of −7.17 and −7.14 respectively against Rhipicephalus microplus acetylcholinesterase protein. Based on obtained result, we believe that Berberium lyceum and Tamarixa aphylla bioactive components could be potential candidates in the control and management of Rhipicephalus microplus and should be studied further as a supplement or replacement for synthetic acaricides.

Acaricide resistance in livestock ticks infesting cattle in Africa: Current status and potential mitigation strategies

In many African countries, tick control has recently been the responsibility of resource-poor farmers rather than central government veterinary departments. This has led to an increase in acaricide resistance, threatening the welfare of livestock farmers in sub-Saharan Africa. Resistance has evolved to the three classes of acaricides used most extensively in the continent, namely fourth-generation synthetic pyrethroids (SP), organophosphates (OP) and amidines (AM), in virtually all countries in which they have been deployed across the globe. Most current data are derived from research in Australia and Latin America, with the majority of studies on acaricide resistance in Africa performed in South Africa. There is also limited recent research from West Africa and Uganda. These studies confirm that acaricide resistance in cattle ticks is a major problem in Africa. Resistance is most frequently directly assayed in ticks using the larval packet test (LPT) that is endorsed by FAO, but such tests require a specialist tick-rearing laboratory and are relatively time consuming. To date they have only been used on a limited scale in Africa and resistance is often still inferred from tick numbers on animals. Rapid tests for resistance in ticks, would be better than the LPT and are theoretically possible to develop. However, these are not yet available. Resistance can be mitigated through integrated control strategies, comprising a combination of methods, including acaricide class rotation or co-formulations, ethnoveterinary practices, vaccination against ticks and modified land management use by cattle, with the goal of minimising the number of acaricide applications required per year. There are data suggesting that small-scale farmers in Africa are often unaware of the chemical differences between different acaricide brands and use these products at concentrations other than those recommended by the manufacturers, or in incorrect rotations or combinations of the different classes of chemicals on the market. There is an urgent need for a more evidence-based approach to acaricide usage in small-scale livestock systems in Africa, including direct measurements of resistance levels, combined with better education of farmers regarding acaricide products and how they should be deployed for control of livestock ticks.

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Resistance to all fourth-generation acaricides is widespread in cattle ticks and is a major problem in Africa.

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Acaricide resistance monitoring through the larval packet tests is mostly absent.

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The integration of ethnoveterinary products with synthetic acaricides is a promising strategy.

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Strengthening laboratory testing and farmersʼ education can lead to rational acaricide use.

Assessment of lipid profile in fat body and eggs of Rhipicephalus microplus engorged females exposed to (E)-cinnamaldehyde and α-bisabolol, potential acaricide compounds

In the present study, the lipid profile from the fat body and eggs of Rhipicephalus microplus was evaluated after exposure of engorged females to (E)-cinnamaldehyde and α-bisabolol, substances which have acaricide potential according to the literature. Engorged females collected from artificially infested cattle were immersed in a concentration of 10.0 mg/mL of each substance. Dissection of the female fat bodies was performed at different times (72 h and 120 h), for subsequent lipid extraction. In addition, on the fifth day of oviposition, were collected 50.0 ml50.0 mL aliquots of the egg mass of each treatment to perform the same lipid extraction procedure. To assess the lipid profiles, the samples were submitted to the thin layer chromatography (TLC) and gas chromatography-mass spectrometry (GCMS) analysis. Furthermore, an in silico analysis was performed using PASS online® software to predict the possible molecular targets of (E)-cinnamaldehyde and α-bisabolol. As result, the main lipids identified from the fat body were triacylglycerides, fatty acids, and cholesterol, whereas, triacylglycerides (TAG), fatty acids (FA), and cholesterol (CHO) and cholesterol esters (CHOE), were identified in the eggs. The results also showed a significant increase (p < 0.05) of CHO in the fat body in the group exposed to (E)-cinnamaldehyde at 72 h (0.12 μg/fat body) and 120 h (0.46 μg/fat body), in the eggs from females treated with this same substance, there was a significant reduction (p < 0.05) in the amount of CHO (0.21 μg), compared to the water control group (0.45 μg). In the GCMS technique, 5 chemical classes were found, and variations were observed between these substances, mainly hydrocarbons and steroids, in the different groups, and (E)-cinnamaldehyde promoted the greatest changes. From the predictions of the in silico study, 38 and 20 targets were selected, respectively, which are mainly related to alterations in lipid metabolism, immune system and nervous system. This study provides the first report of changes in lipid metabolism of R. microplus exposed to (E)-cinnamaldehyde and α-bisabolol, as well as presenting possible activity on the molecular targets of these substances, expanding knowledge for the potential use of these compounds in the development of botanical acaricides.

Effects of essential oils on native and recombinant acetylcholinesterases of Rhipicephalus microplus

This study reports the action of essential oils (EO) from five plants on the activity of native and recombinant acetylcholinesterases (AChE) from Rhipicephalus microplus. Enzyme activity of native susceptible AChE extract (S.AChE), native resistant AChE extract (R.AChE), and recombinant enzyme (rBmAChE1) was determined. An acetylcholinesterase inhibition test was used to verify the effect of the EO on enzyme activity. EO from Eucalyptus globulus, Citrus aurantifolia, Citrus aurantium var.dulcis inhibited the activity of S.AChE and R.AChE. Oils from the two Citrus species inhibited S.AChE and R.AChE in a similar way while showing greater inhibition on R.AChE. The oil from E. globulus inhibited native AChE, but no difference was observed between the S.AChE and R.AChE; however, 71% inhibition for the rBmAChE1 was recorded. Mentha piperita oil also inhibited S.AChE and R.AChE, but there was significant inhibition at the highest concentration tested. Cymbopogon winterianus oil did not inhibit AChE. Further studies are warranted with the oils from the two Citrus species that inhibited R.AChE because of the problem with R. microplus resistant to organophosphates, which target AChE. C. winterianus oil can be used against R. microplus populations that are resistant to organophosphates because its acaricidal properties act by mechanism(s) other than AChE inhibition.

Acaricidal activity of the essential oil from Senecio cannabifolius and its constituents eucalyptol and camphor on engorged females and larvae of Rhipicephalus microplus (Acari: Ixodidae)

The objective of this experiment was to evaluate the acaricidal activity of Senecio cannabifolius essential oil, and two of its constituents, eucalyptol and camphor. Efficacy against females and larvae of Rhipicephalus (Boophilus) microplus was assessed by the adult immersion test (AIT) and the larval immersion test (LIT). The oil was analyzed by gas chromatography-flame ionization detection (GC-FID) and GC-mass spectrometry (MS) and in total 68 components were identified representing 99.2% of the essential oil. AIT revealed that the oil, eucalyptol, and camphor at the highest concentration presented efficacy of 68.9, 57.1, and 71.9%, respectively. LIT revealed that the essential oil and camphor achieved 100% mortality at concentration of 1.6% wt/vol, whereas eucalyptol showed moderate inhibitory activity. Biochemical assays indicated that the essential oil and camphor can reduce significantly overall detoxification enzyme activities in engorged females and larvae at high concentration (≥ 0.4% wt/vol), whereas the inhibitory effect of eucalyptol is weaker than that of the oil and camphor. Taken together our results indicated that the S. cannabifolius essential oil and its isolated constituent had potential for the development of a new and safe acaricide for the control of R. microplus ticks.

In Silico Studies of Lamiaceae Diterpenes with Bioinsecticide Potential against Aphis gossypii and Drosophila melanogaster

Background: The growing demand for agricultural products has led to the misuse/overuse of insecticides; resulting in the use of higher concentrations and the need for ever more toxic products. Ecologically, bioinsecticides are considered better and safer than synthetic insecticides; they must be toxic to the target organism, yet with low or no toxicity to non-target organisms. Many plant extracts have seen their high insecticide potential confirmed under laboratory conditions, and in the search for plant compounds with bioinsecticidal activity, the Lamiaceae family has yielded satisfactory results. Objective: The aim of our study was to develop computer-assisted predictions for compounds with known insecticidal activity against Aphis gossypii and Drosophila melanogaster. Results and conclusion: Structure analysis revealed ent-kaurane, kaurene, and clerodane diterpenes as the most active, showing excellent results. We also found that the interactions formed by these compounds were more stable, or presented similar stability to the commercialized insecticides tested. Overall, we concluded that the compounds bistenuifolin L (1836) and bistenuifolin K (1931), were potentially active against A. gossypii enzymes; and salvisplendin C (1086) and salvixalapadiene (1195), are potentially active against D. melanogaster. We observed and highlight that the diterpenes bistenuifolin L (1836), bistenuifolin K (1931), salvisplendin C (1086), and salvixalapadiene (1195), present a high probability of activity and low toxicity against the species studied.

The potential of Allium sativum and Cannabis sativa extracts for anti-tick activities against Rhipicephalus (Boophilus) microplus

The efficacy of Allium sativum and Cannabis sativa against Rhipicephalus microplus ticks was evaluated using the adult immersion and the larval packet test. In addition, an in silico approach was utilized by performing a docking study in order to identify the active ingredients from both plants. Results showed a comparatively high lethal effect of A. sativum and C. sativa on egg laying (index of egg laying = 0.26 and 0.24, respectively), egg hatching (33.5 and 37.1, respectively), and total larval mortality (100%, both), at 40 mg/mL. When applied to cattle which had been inoculated with larvae ticks, it was observed that a 45% solution of both herbal extracts significantly reduced the number of ticks by 96 h post treatment. We analyzed in silico 27 known active molecules from both plants and identified in the PubChem database to explore the hypothesis that the effect found on ticks was based on inhibition of acetylcholinesterase (AChE). Vitamin E and cannabidiol are the most potent AChE inhibitors with docking scores of -15.85 and -14.38, respectively. Based on these findings, we conclude that A. sativum and C. sativa may potentially be used for the control of R. microplus, and should be further investigated as a potential supplement to or replacement of synthetic acaricides.

Terpenes on Rhipicephalus (Boophilus) microplus: Acaricidal activity and acetylcholinesterase inhibition

The Rhipicephalus (Boophilus) microplus tick is the main ectoparasite of cattle in tropical and subtropical regions worldwide. Resistance to chemical acaricides has become widespread affirming the need for new drugs to tick control. Terpenes have become a promising alternative for cattle tick control, however the mechanism of action of these compounds is still controversial. Inhibition of acetylcholinesterase (AChE) is a well established mechanism of action of organophosphate and carbamate acaricides, but the possible action of terpenes on tick AChEs has seldom been studied in resistant and sensitive strains of R. (B.) microplus. The aim of the present study was to evaluate terpene inhibition of AChE from resistant and sensitive strains of R. (B.) microplus in correlation with their acaricidal activity. Among the terpenes used in the present study, p-cymene, thymol, carvacrol, and citral displayed acaricidal activity with LC₅₀ of 1.75, 1.54, 1.41, and 0.38 mg.mL^-1 for the susceptible strain, and LC₅₀ of 1.40, 1.81, 1.10, and 1.13 mg.mL^-1 for the resistant strain. Thymol and carvacrol inhibited the AChE of the susceptible strain larvae with IC₅₀ of 0.93 and 0.04 mg.mL^-1, respectively. The IC₅₀ exhibited by eucalyptol, carvacrol and thymol for AChE of the resistant strain larvae were 0.36, 0.28, and 0.13 mg.mL^-1, respectively. This was the first study to investigate the action of terpenes on AChE from susceptible and resistant R. (B.) microplus. As not all terpenes with acaridical activity showed AChE inhibition, the participation of AChE in the acaricidal activity of terpenes needs further investigation.

Molecular mechanism of synthetic pyrethroid and organophosphate resistance in field isolates of Rhipicephalus microplus tick collected from a northern state of India

The frequently used chemical control method to manage Rhipicephalus microplus is limited by the emergence of resistance populations. Understanding of resistance mechanisms is essential to develop strategy for sustainable management. The present study was focused on working out the molecular mechanisms of resistance against synthetic pyrethroids (SPs) and organophosphates (OPs) in field isolates of R. microplus collected from six districts of Uttar Pradesh, India. Adult immersion test with discriminating concentrations (AIT-DC) was used to determine resistance status of isolates to SPs (deltamethrin, cypermethrin) and OPs (diazinon, coumaphos). All the six isolates were found resistant to SPs with resistance factor (RF) of 2.9-58.6 and to one of the OP compounds, diazinon having RF of 3.5-13.7 but susceptible to coumaphos (RF < 1.4). Three R. microplus genes, viz. para-sodium channel domain II S4-5 linker, carboxylesterase (372 bp) and acetylcholinesterase 2 (1692 bp) were sequenced and compared with respective sequences of reference susceptible IVRI-I, reference OP resistant population (IVRI-III), IVRI-IV and multi-acaricide resistant population (IVRI-V) of R. microplus. A C190A mutation in the domain II S4-5 linker region of sodium channel gene leading to L64I amino acid substitution was detected in all six isolates. The G1120A mutation in the carboxylesterase gene could not be detected in any isolate. Five nucleotide substitutions viz., G138A, G889A, T1090A, C1234T and G1403A were identified in the acetylcholinesterase 2 gene leading to four amino acid substitutions. The findings of the study corroborate the role of mutation in sodium channel and acetylcholinesterase 2 genes in SP and OP resistance in this part of India.

Natural genomic amplification of cholinesterase genes in animals

Tight control of the concentration of acetylcholine at cholinergic synapses requires precise regulation of the number and state of the acetylcholine receptors, and of the synthesis and degradation of the neurotransmitter. In particular, the cholinesterase activity has to be controlled exquisitely. In the genome of the first experimental models used (man, mouse, zebrafish and drosophila), there are only one or two genes coding for cholinesterases, whereas there are more genes for their closest relatives the carboxylesterases. Natural amplification of cholinesterase genes was first found to occur in some cancer cells and in insect species subjected to evolutionary pressure by insecticides. Analysis of the complete genome sequences of numerous representatives of the various metazoan phyla show that moderate amplification of cholinesterase genes is not uncommon in molluscs, echinoderms, hemichordates, prochordates or lepidosauria. Amplification of acetylcholinesterase genes is also a feature of parasitic nematodes or ticks. In these parasites, over-production of cholinesterase-like proteins in secreted products and the saliva are presumed to have effector roles related to host infection. These amplification events raise questions about the role of the amplified gene products, and the adaptation processes necessary to preserve efficient cholinergic transmission. This is an article for the special issue XVth International Symposium on Cholinergic Mechanisms.

Identification of a novel β-adrenergic octopamine receptor-like gene (βAOR-like) and increased ATP-binding cassette B10 (ABCB10) expression in a Rhipicephalus microplus cell line derived from acaricide-resistant ticks

Background

The cattle tick Rhipicephalus (Boophilus) microplus is an economically important parasite of livestock. Effective control of ticks using acaricides is threatened by the emergence of resistance to many existing compounds. Several continuous R. microplus cell lines have been established and provide an under-utilised resource for studies into acaricide targets and potential genetic mutations associated with resistance. As a first step to genetic studies using these resources, this study aimed to determine the presence or absence of two genes and their transcripts that have been linked with acaricide function in cattle ticks: β-adrenergic octopamine receptor (βAOR, associated with amitraz resistance) and ATP-binding cassette B10 (ABCB10, associated with macrocyclic lactone resistance) in six R. microplus cell lines, five other Rhipicephalus spp. cell lines and three cell lines representing other tick genera (Amblyomma variegatum, Ixodes ricinus and Hyalomma anatolicum).

Methods

End-point polymerase chain reaction (PCR) was used for detection of the βAOR gene and transcripts in DNA and RNA extracted from the tick cell lines, followed by capillary sequencing of amplicons. Quantitative real-time PCR (qPCR) was performed to determine the levels of expression of ABCB10.

Results

βAOR gene expression was detected in all Rhipicephalus spp. cell lines. We observed a second amplicon of approximately 220 bp for the βAOR gene in the R. microplus cell line BME/CTVM6, derived from acaricide-resistant ticks. Sequencing of this transcript variant identified a 36 bp insertion in the βAOR gene, leading to a 12-amino acid insertion (LLKTLALVTIIS) in the first transmembrane domain of the protein. In addition, nine synonymous SNPs were also discovered in R. appendiculatus, R. evertsi and R. sanguineus cell lines. Some of these SNPs appear to be unique to each species, providing potential tools for differentiating the tick species. The BME/CTVM6 cell line had significantly higher ABCB10 (P = 0.002) expression than the other R. microplus cell lines.

Conclusions

The present study has identified a new βAOR gene and demonstrated a higher ABCB10 expression level in the BME/CTVM6 cell line, indicating that tick cell lines provide a useful experimental tool for acaricide resistance studies and further elucidation of tick genetics.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1708-x) contains supplementary material, which is available to authorized users.

Tick Salivary Cholinesterase: A Probable Immunomodulator of Host-parasite Interactions

The southern cattle tick, Rhipicephalus (Boophilus) microplus (Canestrini), is the most economically important cattle ectoparasite in the world. Rhipicephalus microplus and Rhipicephalus annulatus (Say) continue to threaten U.S. cattle producers despite eradication and an importation barrier based on inspection, dipping of imported cattle in organophosphate (OP) acaricide, and quarantine of infested premises. OP acaricides inhibit acetylcholinesterase (AChE), essential to tick central nervous system function. Unlike vertebrates, ticks possess at least three genes encoding AChEs, differing in amino acid sequence and biochemical properties. Genomic analyses of R. microplus and the related tick, Ixodes scapularis, suggest that ticks contain many genes encoding different AChEs. This work is the first report of a salivary cholinesterase (ChE) activity in R. microplus, and discusses complexity of the cholinergic system in ticks and significance of tick salivary ChE at the tick-host interface. It further provides three hypotheses that the salivary ChE plausibly functions 1) to reduce presence of potentially toxic acetylcholine present in the large bloodmeal imbibed during rapid engorgement, 2) to modulate the immune response (innate and/or acquired) of the host to tick antigens, and 3) to influence transmission and establishment of pathogens within the host animal. Ticks are vectors for a greater number and variety of pathogens than any other parasite, and are second only to mosquitoes (owing to malaria) as vectors of serious human disease. Saliva-assisted transmission (SAT) of pathogens is well-known; however, the salivary components participating in the SAT process remain to be elucidated.

Paralog analyses reveal gene duplication events and genes under positive selection in Ixodes scapularis and other ixodid ticks

Background

Hard ticks (family Ixodidae) are obligatory hematophagous ectoparasites of worldwide medical and veterinary importance. The haploid genomes of multiple species of ixodid ticks exceed 1 Gbp, prompting questions regarding gene, segmental and whole genome duplication in this phyletic group. The availability of the genome assembly for the black legged tick, Ixodes scapularis, and transcriptome datasets for multiple species of ticks offers an opportunity to assess the contribution of gene duplication to the genome. Here we developed a bioinformatics pipeline to identify and analyze duplicated genes (paralogs) using gene models from the prostriate tick, I. scapularis IscaW1.1 annotation and expressed sequence tags (ESTs) from I. scapularis and the metastriate ticks, Rhipicephalus microplus (southern cattle tick), R. appendiculatus (brown ear tick) and Amblyomma variegatum (tropical bont tick).

Results

Approximately 1-2 % of I. scapularis gene models and 2-14 % of ESTs from the four species represent duplicated genes. The ratio of non-synonymous to synonymous nucleotide substitution rates suggests ~ 25 % of duplicated genes are under positive selection pressure in each species. Analyses of synonymous substitution rates provide evidence for two duplication events in I. scapularis and R. microplus involving several hundred genes. Conservative molecular clock estimates based on synonymous substitution rates for species of Anopheles mosquitoes and the fruit fly, Drosophila melanogaster, suggest these events occurred within the last 50 MYA. Mapping of paralogs to the I. scapularis genome assembly supports tandem, or possibly segmental duplication events.

Conclusions

The present study marks the first genome-level analyses of gene duplication for the Ixodidae and provides insights into mechanisms shaping genome evolution in this group. At least two duplication events involving hundreds of genes may have occurred independently in the lineages prostriata and metastriata, with tandem and segmental duplication the most likely mechanisms for paralog generation. Duplicated genes under positive selection pressure may be linked to emerging functions in the tick and represent important candidates for further study.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-2350-2) contains supplementary material, which is available to authorized users.

Identification of 24h Ixodes scapularis immunogenic tick saliva proteins

Ixodes scapularis is arguably the most medically important tick species in the United States. This tick transmits 5 of the 14 human tick-borne disease (TBD) agents in the USA: Borrelia burgdorferi, Anaplasma phagocytophilum, B. miyamotoi, Babesia microti, and Powassan virus disease. Except for the Powassan virus disease, I. scapularis-vectored TBD agents require more than 24h post attachment to be transmitted. This study describes identification of 24h immunogenic I. scapularis tick saliva proteins, which could provide opportunities to develop strategies to stop tick feeding before transmission of the majority of pathogens. A 24h fed female I. scapularis phage display cDNA expression library was biopanned using rabbit antibodies to 24h fed I. scapularis female tick saliva proteins, subjected to next generation sequencing, de novo assembly, and bioinformatic analyses. A total of 182 contigs were assembled, of which ∼19% (35/182) are novel and did not show identity to any known proteins in GenBank. The remaining ∼81% (147/182) of contigs were provisionally identified based on matches in GenBank including ∼18% (27/147) that matched protein sequences previously annotated as hypothetical and putative tick saliva proteins. Others include proteases and protease inhibitors (∼3%, 5/147), transporters and/or ligand binding proteins (∼6%, 9/147), immunogenic tick saliva housekeeping enzyme-like (17%, 25/147), ribosomal protein-like (∼31%, 46/147), and those classified as miscellaneous (∼24%, 35/147). Notable among the miscellaneous class include antimicrobial peptides (microplusin and ricinusin), myosin-like proteins that have been previously found in tick saliva, and heat shock tick saliva protein. Data in this study provides the foundation for in-depth analysis of I. scapularis feeding during the first 24h, before the majority of TBD agents can be transmitted.

Transcriptome of the female synganglion of the black-legged tick Ixodes scapularis (Acari: Ixodidae) with comparison between Illumina and 454 systems

Illumina and 454 pyrosequencing were used to characterize genes from the synganglion of female Ixodes scapularis. GO term searching success for biological processes was similar for samples sequenced by both methods. However, for molecular processes, it was more successful for the Illumina samples than for 454 samples. Functional assignments of transcripts predicting neuropeptides, neuropeptide receptors, neurotransmitter receptors and other genes of interest was done, supported by strong e-values (<-6), and high consensus sequence alignments. Transcripts predicting 15 putative neuropeptide prepropeptides ((allatostatin, allatotropin, bursicon α, corticotropin releasing factor (CRF), CRF-binding protein, eclosion hormone, FMRFamide, glycoprotein A, insulin-like peptide, ion transport peptide, myoinhibitory peptide, inotocin ( =  neurophysin-oxytocin), Neuropeptide F, sulfakinin and SIFamide)) and transcripts predicting receptors for 14 neuropeptides (allatostatin, calcitonin, cardioacceleratory peptide, corazonin, CRF, eclosion hormone, gonadotropin-releasing hormone/AKH-like, insulin-like peptide, neuropeptide F, proctolin, pyrokinin, SIFamide, sulfakinin and tachykinin) are reported. Similar to Dermacentor variabilis, we found transcripts matching pro-protein convertase, essential for converting neuropeptide hormones to their mature form. Additionally, transcripts predicting 6 neurotransmitter/neuromodulator receptors (acetylcholine, GABA, dopamine, glutamate, octopamine and serotonin) and 3 neurotransmitter transporters (GABA transporter, noradrenalin-norepinephrine transporter and Na+-neurotransmitter/symporter) are described. Further, we found transcripts predicting genes for pheromone odorant receptor, gustatory receptor, novel GPCR messages, ecdysone nuclear receptor, JH esterase binding protein, steroidogenic activating protein, chitin synthase, chitinase, and other genes of interest. Also found were transcripts predicting genes for spermatogenesis-associated protein, major sperm protein, spermidine oxidase and spermidine synthase, genes not normally expressed in the female CNS of other invertebrates. The diversity of messages predicting important genes identified in this study offers a valuable resource useful for understanding how the tick synganglion regulates important physiological functions.

Acetylcholinesterase activity in the host-parasite system of the cod Gadus morhua and acanthocephalan Echinorhynchus gadi from the southern Baltic Sea

Acetylcholinesterase (AChE) activity measurement is widely used as a specific biomarker of neurotoxic effects. The aim of this study was to evaluate AChE activity in a host fish (the cod) and its acanthocephalan parasite Echinorhynchus gadi from the southern Baltic. AChE activity in hosts and parasites was inversely related: the highest cod AChE activity corresponded to the lowest E. gadi enzymatic activity and vice versa ("mirror effect"). This is the first report on the simultaneous application of this biomarker in cod and its acanthocephalan parasites. Results obtained for the host-parasite system are complementary and provide comprehensive information about the response of this biomarker. Analysis of the system allows for detection of a greater number of factors influencing AChE activity in the marine environment than separate analysis of the host and parasites. Thus, AChE activity measurement in a host-parasite system may be considered to be a promising tool for biomonitoring.