Strategies for the control of Rhipicephalus microplus ticks in a world of conventional acaricide and macrocyclic lactone resistance

Acaricidal and Repellent Effects of Essential Oils against Ticks: A Review

Tick control is a priority in order to prevent the transmission of vector-borne diseases. Industrial chemical acaricides and repellents have been the most efficient tools against hard ticks for a long time. However, the appearance of resistances has meant the declining effectiveness of the chemicals available on the market. The trend today is to develop alternative control methods using natural products to replace nonefficient pesticides and to preserve the efficient ones, hoping to delay resistance development. Traditional in vitro evaluation of acaricidal activity or resistance to synthetic pesticides have been reviewed and they mainly focus on just one species, the one host tick (Rhipicephalus (Boophilus) microplus (Acari: Ixodidae)). Recent reports have called for the standardization of natural product components, extraction techniques, and experimental design to fully discover their acaricidal potential. This study reviews the main variables used in the bibliography about the efficiency of natural products against ticks, and it proposes a unification of variables relating to ticks, practical development of bioassays, and estimation of ixodicidal activity.

Assessment of weight gain and control of parasitism by Rhipicephalus microplus in dairy cattle in the field using organosynthetic parasiticide, phytotherapics and homeopathy

ABSTRACT The goal of this research was to compare the effect of the following products on dairy cattle, parasitized by Rhipicephalus microplus: organosynthetics - Clorfenvinfós and Ivermectina (OG); phytotherapics - Eucalyptus oil (EG) and Neem cake (NG); Homeopathy (HG); The control group (CG) received no treatment. Infestation was by R. microplus (MIC) and weight gain (GP) were evaluated. The study included 60 animals (5 groups) from – Dutch / Zebu, aged between 25-44 months and initial weight between 211-477kg. EG and NG showed MIC 84.9% and 14.0% greater than CG, respectively (P <0.05; P = 0). HG and OG had MIC less than CG 24.4% and 16.9%, respectively (P<0.05; P <0.05). EG, NG and OG obtained GP lower than CG in 7.9%, 8.9% and 8.06% (P <0.05) respectively. The HG GP was 4.9% higher (P <0.05) than CG. This was the first research to prove parasitism control by R. microplus in a field test, using homeopathy. The methodology for choosing Homeopathy for the control of enzooties, developed and tested for the first time in this study, proved to be adequate and efficient, opening the possibility for establishing a new methodology for strategic control of parasitism by R. microplus.

Protective efficacy of the peptide Subolesin antigen against the cattle tick Rhipicephalus microplus under natural infestation

The cattle tick Rhipicephalus microplus affect animal health, welfare, and cattle production in tropical and subtropical zones of the world. Anti-tick vaccines have been an effective alternative for cattle tick control instead of traditional chemical products. To date, Subolesin antigen has shown efficacy for the control of tick infestation in cattle, and previous studies showed that one peptide derived from this protein has demonstrated to elicit a strong and specific humoral immune response. Based on these findings, herein we characterized the efficacy of the peptide Subolesin for the control of cattle tick, R. microplus infestation under field conditions. Twenty-four female calves were assigned to four experimental groups and immunized with three subcutaneous doses of the peptide Subolesin, Bm86, both antigens (dual vaccine) and adjuvant/saline alone, respectively. Serum antibody levels (IgG) were assessed by ELISA and confirmed by Western blot; also, reproductive performance of naturally infested R. microplus was determined. The results showed that immunizations with the experimental antigens reduced tick infestations with vaccine's efficacy of 67 % (peptide Subolesin), 56 % (Bm86), and 49 % (dual vaccine) based on adult tick numbers, oviposition, and egg fertility between vaccinated and control animals. Peptide Subolesin-immunized calves developed a strong humoral immune response expressed by high anti-pSubolesin IgG levels, and the Western blot analysis confirmed that it is immunogenic. Cattle receiving Bm86 and dual vaccine showed less protection, although Bm86 was within the range reported previously. The negative correlation between antibody levels and reduction of naturally infested R. microplus strongly suggested that the effect of the vaccine was the result of the antibody response in immunized cattle. In conclusion, it was demonstrated that the peptide Subolesin induced a specific immune response in cattle under field conditions, resulting in reduced R. microplus populations in subsequent generations. Finally, integrated tick control must consider anti-tick vaccines as a cost-effective, sustainable, and successful tool for controlling cattle tick infestations.

Characterization of a strain of Serratia sp. with ixodicide activity against the cattle tick Rhipicephalus microplus

Cattle ticks are considered the most important ectoparasite in the livestock industry. Rhipicephalus microplus causes economic losses both through direct feeding on livestock and through disease transmission. Reports of the failure of chemical ixodicides to control this tick have led to a search for control alternatives, such as bacteria with ixodicide activity. The objective of this work was to select a bacterial strain with ixodicide activity against R. microplus. In total, 83 bacterial strains were isolated from soil and dead R. microplus specimens, and all strains were evaluated against larvae in a screening test. Bacteria with ixodicide activity were evaluated in larvae and engorged adult female ticks. The larvae were challenged using the larval immersion test (LIT) with 20 µg/mL total protein. The median lethal concentration (LC₅₀) for larvae was obtained by using nine total protein concentrations. Engorged adult female ticks were challenged using the adult immersion test (AIT) with six protein concentrations. We evaluated adult mortality on day 10, oviposition rate on day 14 and hatching rate on day 40 after challenge. Only one bacterial strain (EC-35) showed ixodicide activity against larvae and adult R. microplus. The highest larval mortality, 52.3%, occurred with a total protein concentration of 40 μg/mL, and the LC₅₀ was 13.9 µg/mL of protein. In adults, a total protein concentration of 10 µg/mL had the highest mortality (55%), oviposition inhibition (50.9%) and reproductive potential inhibition (52.5%). However, there was no significant effect on hatching. The 16S rRNA gene sequence showed 99% identity of EC-35 with Serratia sp.

Three-Dimensional Culture of Rhipicephalus (Boophilus) microplus BmVIII-SCC Cells on Multiple Synthetic Scaffold Systems and in Rotating Bioreactors

Tick cell culture facilitates research on the biology of ticks and their role as vectors of pathogens that affect humans, domestic animals, and wildlife. Because two-dimensional cell culture doesn't promote the development of multicellular tissue-like composites, we hypothesized that culturing tick cells in a three-dimensional (3-D) configuration would form spheroids or tissue-like organoids. In this study, the cell line BmVIII-SCC obtained from the cattle fever tick, Rhipicephalus (Boophilus) microplus (Canestrini, 1888), was cultured in different synthetic scaffold systems. Growth of the tick cells on macrogelatinous beads in rotating continuous culture system bioreactors enabled cellular attachment, organization, and development into spheroid-like aggregates, with evidence of tight cellular junctions between adjacent cells and secretion of an extracellular matrix. At least three cell morphologies were identified within the aggregates: fibroblast-like cells, small endothelial-like cells, and larger cells exhibiting multiple cytoplasmic endosomes and granular vesicles. These observations suggest that BmVIII-SCC cells adapted to 3-D culture retain pluripotency. Additional studies involving genomic analyses are needed to determine if BmVIII-SCC cells in 3-D culture mimic tick organs. Applications of 3-D culture to cattle fever tick research are discussed.

Assessing HeberFast® Line Gavac, a lateral flow immunochromatographic system for the rapid detection of anti-Bm86 antibodies in Gavac vaccinated cattle

Rhipicephalus Boophilus microplus cattle tick is a scourge for livestock production. The infestations produced by this pathogen are incompletely contained by chemical treatments, with the associated environmental pollution risks. Vaccination against cattle ticks has emerged as a feasible and environmentally friendly strategy to control tick-borne diseases. In this setting, Gavac® vaccine has proven effective in decreasing cattle tick populations through antibody responses against the tick Bm86 antigen, as part of an Integrated Control Program. However, animal vaccination programs require easy and ready-to-use screening tests to follow up the immune response in vaccinated animals under field conditions. This study reports the evaluation HeberFast® Line Gavac, a lateral flow immunochromatographic system for the rapid detection of anti Bm86 antibodies in vaccinated cattle. The system was tested on 598 serum samples taken from immunized animals, arranged in three groups according to their anti-Bm86 antibody response in ELISA (209 high, 150 medium or 239 low and 100 samples from non-immunized animals. The HeberFast® Line Gavac system was assessed for sensitivity, specificity, and concordance against the ELISA reference test. Consistency was evaluated among production batches and inter-analyst reading-independent consistency at two moments: ten minutes after completing the test and after strip drying. The system showed high sensitivity (81.6%, 82.2%, and 81%), specificity (96.7, 94.6, and 93.3%), and agreement with the ELISA reference test (75%; 74%, and 71%) for high, medium and low anti-Bm86 sera, respectively. The effectiveness of the diagnosis was 87.6; 87.1; 85.9 for high, medium, and low antibody titers, respectively. Consistency among production batches and analysts was documented, and no significant differences between evaluation times were found. These results indicate that HeberFast® Line Gavac is a valuable tool for the serological surveillance of Gavac vaccinated cattle.

Acaricidal activity and clinical safety of arecoline hydrobromide on calves infested with cattle tick Rhipicephalus microplus (Acari: Ixodidae)

The objective of the present study was to determine the acaricidal activity of arecoline hydrobromide against cattle tick Rhipicephalus microplus infesting calves. in vivo efficacy of arecoline emulsified with polysorbate-80 (2%) was evaluated using ear bag method with the effective dose of 12.5 mg/mL applied on ear pinna of calves infested with ticks. Control group received polysorbate-80 (2%) after larvae infestation, however, reference group received deltamethrin (0.5 %). The experiment was continued for six days (144 h) and treatment of drug was given twice a day. Daily observation of calves was done to count the number of ticks after treatment. Acute dermal toxicity study for test drug was performed on wistar rats. Clinical safety of arecoline was determined by examining hematological profile and skin irritancy assay for calves infested with ticks. Results showed that arecoline significantly (p < 0.01) reduced the number of ticks attached to ear pinna of calves. Fewer number of ticks remained on calves skin at 120 h and 144 h were 8.09 and 6.21, respectively after treatment with arecoline in comparison to control group. Treatment of animals with arecoline hydrobromide significantly (p < 0.01) restored the hematological profile of animals as hemoglobin (Hb) level was 9.01 g/100 mL, PVC was 29.24 %, TEC and TLC were 5.23 and 7.19 106/cumm, respectively as compared to the control group having Hb 9.48 g/100 mL, PVC 31.60 %, TEC 5.64 10⁶/cumm and TLC 7.27 10⁶/cumm. Arecoline showed no toxicity while applied on wistar rats. The drug was mild irritative for an initial 20 min to the calves after that no redness or erythema was seen on the skin of the animals. Thus, arecoline hydrobromide may be an effective alternative to be used as herbal ectoparasiticide for the eradication of R. microplus ticks.

Resistance to Ticks and the Path to Anti-Tick and Transmission Blocking Vaccines

The medical and veterinary public health importance of ticks and tick-borne pathogens is increasing due to the expansion of the geographic ranges of both ticks and pathogens, increasing tick populations, growing incidence of tick-borne diseases, emerging tick transmitted pathogens, and continued challenges of achieving effective and sustained tick control. The past decades show an increasing interest in the immune-mediated control of tick infestations and pathogen transmission through the use of vaccines. Bovine tick resistance induced by repeated infestations was reported over a century ago. This review addresses the phenomena and immunological underpinning of resistance to tick infestation by livestock and laboratory animals; the scope of tick countermeasures to host immune defenses; and the impact of genomics, functional genomics, and proteomics on dissecting complex tick-host-pathogen interactions. From early studies utilizing tick tissue extracts to salivary gland derived molecules and components of physiologically important pathways in tick gut and other tissues, an increased understanding of these relationships, over time, impacted the evolution of anti-tick vaccine antigen selection. Novel antigens continue to emerge, including increased interest in the tick microbiome. Anti-tick and transmission blocking vaccines targeting pathogen reservoirs have the potential to disrupt enzootic cycles and reduce human, companion, domestic animal, and wildlife exposure to infected ticks.

Optimizing long-acting acaricide use for integrated tick management of Rhipicephalus australis-infesting cattle in New Caledonia

The tick Rhipicephalus australis, formerly known as Rhipicephalus microplus, is the most economically important ectoparasite of livestock in New Caledonia, affecting cattle health and production. Decades of control attempts based on the application of chemical acaricides have exerted a strong selective pressure on R. australis populations, some of which have evolved resistance to these treatments. Research to develop integrated tick control programs is now focused on decreasing applications of chemicals. This study reports the implementation of a method of pasture and herd management involving minimal strategic use of long-acting acaricides, here defined as those having substantial efficacy against larvae for several weeks. Diverse parameters concerning the utilization of long-acting acaricides in association with pasture and herd management on 21 New Caledonian farms over a 5-year period were analyzed to optimize their strategic use. Longer larval acaricidal effect was achieved with a commercial pour-on formulation of fluazuron than with a commercial injectable (subcutaneous) formulation containing 3.15% ivermectin. Pasture and herd management allowed an increase in the delay between a long-lasting acaricide application and the subsequent acaricide treatment from 11.0 weeks to 17.7 weeks. However, if ticks were detected and reported by producers on the day of a long-acting acaricide application, the delay to the following treatment was reduced from 18.5 weeks to 11.2 weeks. The impact of a long-acting acaricide treatment on larval populations in pastures was greatest with a stocking rate of 5 animals per hectare grazing during 1 week. These results provide science-based evidence to cattle producers for adaptive integrated tick management in order to delay the development of acaricide resistance.

Rhipicephalus Tick: A Contextual Review for Southeast Asia

Rhipicephalus species are distributed globally with a notifiable presence in Southeast Asia (SEA) within animal and human populations. The Rhipicephalus species are highly adaptive and have established successful coexistence within human dwellings and are known to be active all year round, predominantly in tropical and subtropical climates existing in SEA. In this review, the morphological characteristics, epidemiology, and epizootiology of Rhipicephalus tick species found in SEA are reviewed. There are six commonly reported Rhipicephalus ticks in the SEA region. Their interactions with their host species that range from cattle, sheep, and goats, through cats and dogs, to rodents and man are discussed in this article. Rhipicephalus-borne pathogens, including Anaplasma species, Ehrlichia species, Babesia species, and Theileria species, have been highlighted as are relevant to the region in review. Pathogens transmitted from Rhipicepahalus ticks to host animals are usually presented clinically with signs of anemia, jaundice, and other signs of hemolytic changes. Rhipicephalus ticks infestation also account for ectoparasitic nuisance in man and animals. These issues are discussed with specific interest to the SEA countries highlighting peculiarities of the region in the epidemiology of Rhipicephalus species and attendant pathogens therein. This paper also discusses the current general control strategies for ticks in SEA proffering measures required for increased documentation. The potential risks associated with rampant and improper acaricide use are highlighted. Furthermore, such practices lead to acaricide resistance among Rhipicephalus species are highlighted.

First report on efficacy of Citrus limetta seed oil in controlling cattle tick Rhipicephalus microplus in red Sahiwal calves

The objective of the study was to evaluate the acaricidal activity of Citrus limetta seed oil (CLO) for controlling the cattle tick Rhipicephalus microplus. C. limetta seeds were collected as a waste product from different juice corners. CLO was obtained after extraction of seeds on soxhlet apparatus using n-hexane as solvent. It was characterized through Gas Chromatography-High Resolution Mass Spectroscopy (GC-HRMS) to determine the presence of active constituents. In vitro bioassays were performed using adult immersion test (AIT) and larval packet test (LPT). In vivo acaricidal efficacy of CLO was performed on red Sahiwal calves using ear bag method. Clinical safety of CLO was evaluated by observing haematological parameters and skin irritancy assay. Results of GC-HRMS showed that mainly fatty acids such as linoleic acid, stearic acid, oleic acid, palmitic acid, and linolenic acid were present in the CLO. CLO in the concentration of 125 mg/mL (CLO8) exhibited 100 % mortality in both AIT and LPT. CLO significantly (p < 0.001) reduced the number of ticks from 35 to 5.05 and 3.24 on 144 h after treatment with CLO7 and CLO8, respectively. CLO was found clinically safe without producing erythema and edema on skin. Haematological parameters such as haemoglobin (11.48 g/100 mL), total leucocytes count (4.32 10⁶/cumm), total erythrocytes count (6.80 10⁶/cumm), and packed cell volume (34.39 %) were normal and controlled. CLO may be used as effective and safe drug therapy for controlling R. microplus ticks.

Rhipicephalus microplus seasonal dynamic in a Cerrado biome, Brazil: An update data considering the global warming

The present study evaluated over two years the seasonal dynamics of Rhipicephalus microplus in a Cerrado biome of midwestern Brazil (Goiânia, Goiás) and correlated the current climatic conditions (environmental temperature, insolation, rainfall, relative humitidy and saturation deficit of the atmosphere) of this site with 30 years ago. In addition, the data collected in the present research were compared with climatic conditions data and R. microplus population dynamics conducted by our group in other regions (Formiga, Minas Gerais and Jaboticabal, São Paulo) within the same biome. For the parasitic phase dynamics, R. microplus females (4.5-8.0 mm) counts were performed on tick natural infested cows kept in Panicum maximum paddocks. To verify the larvae dynamics on pasture the flannel dragg technique on natural infested pasture was performed, and the height of the grass was measured. Five peaks of engorged R. microplus females on animals and larvae infestations on pastures were observed. Being three and two peaks during the rainy and dry season of the year, respectively. Insolation (r = 0.8758; P = 0.00009; R² = 0.7670), rainfall (r = -0.8572; P = 0.0002; R² = 0.7348), maximum environmental temperature in summer (r = 0.9999; P < 0.0087; R² = 0.9988) and the saturation deficit of the atmosphere in autumn (r = -0.9789; P = 0.0211; R² = 0.9582) influenced the seasonal dynamics of R. microplus larvae on pastures. While the forage height did not influence the number of larvae found on pasture (r = 0.1545; P = 0.7682; R² = 0.0239). The comparison between the climatic data of the last 30 years with the current climatological data (2012 to 2019) in the state of Goiás, and the comparison with R. microplus population dynamics from other two locations in the same biome indicated that the increase of the environmental temperature due to the global warming possibly is a determining factor which increase the number of one or up two tick annual peaks. In addition, this climatic variable was responsible for increase the population density of ticks on pastures and animals observed in July/winter of the present study, in comparison to other regions with the same biome, as discussed in this work.

Cattle ticks and tick-borne diseases: a review of Uganda's situation

Herein we review the epidemiology of ticks and tick-borne diseases (TTBDs), their impact on livestock health and on the economy, control and associated challenges in Uganda. Ticks are leading vectors of economically important pathogens and are widespread in Uganda due to suitable climatic conditions. Besides the physical injury inflicted on the animal host, ticks transmit a number of pathogens that can cause morbidity and mortality of livestock if untreated, resulting in economic losses. Uganda suffers an aggregated annual loss (direct and indirect) of over USD 1.1 billion in the TTBDs complex. East Coast fever (ECF) caused by a protozoan haemoparasite, Theileria parva, is the most prevalent and economically important tick-borne disease (TBD) in Uganda and its vector, the brown ear tick (Rhipicephalus appendiculatus) widely distributed. Other prevalent TBDs in Uganda include anaplasmosis, babesiosis and heartwater. We highlight the role of agro-ecological zones (AEZs) and livestock management system in the distribution of TTBDs, citing warm and humid lowlands as being ideal habitats for ticks and endemic for TBDs. Control of TTBDs is a matter of great importance as far as animal health is concerned in Uganda. Indigenous cattle, which make up over 90% of the national herd are known to be more tolerant to TTBDs and most farms rely on endemic stability to TBDs for control. However, exotic cattle breeds are more capital intensive than indigenous breeds, but the increasing adoption of tick-susceptible exotic cattle breeds (especially dairy) in western and central Uganda demands intensive use of acaricides for tick control and prevention of TBDs. Such acaricide pressure has unfortunately led to selection of acaricide-resistant tick populations and the consequent acaricide resistance observed in the field. Vaccination against ECF, selective breeding for tick resistance and integrated tick control approaches that limit tick exposure, could be adopted to interrupt spread of acaricide resistance. We recommend increasing monitoring and surveillance for TTBDs and for emerging acaricide resistance, improved extension services and sensitization of farmers on tick control measures, appropriate acaricide use and the development and implementation of vaccines for the control of TTBDs as more sustainable and effective interventions. A tick control policy should be developed, taking into account variations of agro-ecological zones, farm circumstances and indigenous technical knowledge, and this should be incorporated into the overall animal health program.

Entomopathogenic Fungi and Bacteria in a Veterinary Perspective

Simple Summary

Several fungal species are well suited to control arthropods, being able to cause epizootic infection among them and most of them infect their host by direct penetration through the arthropod’s tegument. Most of organisms are related to the biological control of crop pests, but, more recently, have been applied to combat some livestock ectoparasites. Among the entomopathogenic bacteria, Bacillus thuringiensis, innocuous for humans, animals, and plants and isolated from different environments, showed the most relevant activity against arthropods. Its entomopathogenic property is related to the production of highly biodegradable proteins. Entomopathogenic fungi and bacteria are usually employed against agricultural pests, and some studies have focused on their use to control animal arthropods. However, risks of infections in animals and humans are possible; thus, further studies about their activity are necessary.

Abstract

The present study aimed to review the papers dealing with the biological activity of fungi and bacteria against some mites and ticks of veterinary interest. In particular, the attention was turned to the research regarding acarid species, Dermanyssus gallinae and Psoroptes sp., which are the cause of severe threat in farm animals and, regarding ticks, also pets. Their impact on animal and human health has been stressed, examining the weaknesses and strengths of conventional treatments. Bacillus thuringiensis, Beauveria bassiana and Metarhizium anisopliae are the most widely employed agents. Their activities have been reviewed, considering the feasibility of an in-field application and the effectiveness of the administration alone or combined with conventional and alternative drugs is reported.

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.

A random small molecule library screen identifies novel antagonists of the kinin receptor from the cattle fever tick, Rhipicephalus microplus (Acari: Ixodidae)

BACKGROUND

The southern cattle tick, Rhipicephalus microplus, is a primary vector of the deadly bovine disease babesiosis. Worldwide populations of ticks have developed resistance to acaricides, underscoring the need for novel target discovery for tick control. The arthropod-specific R. microplus kinin receptor is such a target, previously validated by silencing, which resulted in female reproductive fitness costs, including a reduced percentage of eggs hatching.

RESULTS

In order to identify potent small molecules that bind and activate or inhibit the kinin receptor, a high-throughput screening (HTS) assay was developed using a CHO-K1 cell line expressing the recombinant tick kinin receptor (BMLK₃ ). A total of ~20 000 molecules from a random in-house small molecule library were screened in a 'dual-addition' calcium fluorescence assay. This was followed by dose-response validation of the hit molecules identified both from HTS and an in silico screen of ~390 000 molecules. We validated 29 antagonists, 11 of them were full antagonists with IC₅₀ values between 0.67 and 8 μmol L^-1 . To explore the structure-activity relationships (SAR) of the small molecules, we tested the activities of seven analogs of the most potent identified antagonist, additionally discovering three full antagonists and four partial antagonists. These three potent antagonists (IC₅₀ < 3.2 μmol L^-1 ) were validated in vitro using the recombinant mosquito kinin receptor and showed similar antagonistic activities. In vivo, these three compounds also inhibited the mosquito hindgut contraction rate induced by a myotropic kinin agonist analog 1728.

CONCLUSION

Antagonists identified in this study could become pesticide leads and are reagents for probing the kinin signaling system. © 2021 Society of Chemical Industry.

Evaluation of different strategic control protocols for Rhipicephalus microplus on cattle according to tick burden

The development of a strategic protocol is fundamental to the control of Rhipicephalus microplus. The efficacy of different strategic tick control protocols (Day 1 to Day 119) using commercial acaricides according to R. microplus burden on bovines was evaluated. Female ticks (4.5-8 mm in length) were initially counted on cattle to form four groups of bovines with low and high tick burdens (treated and control), with 10 animals each. The animals were then (Day 0) kept in different paddocks, and the bovines from the two treated groups received their first treatment. The main difference in the protocols was the use of a spray formulation on animals with high tick burden. Additionally, the criterion for animal re-treatment (treatment interval) during the proposed strategic protocol was evaluated according to tick length by visual inspection - if 30% of the bovines of a group presented ticks < 4 mm between their legs and dewlap, the treatment was applied, which could change the originally proposed intervals. The number of days for which animals from the treated groups remained without acaricide administration (palliative control, ≥30 tick females < 4 mm) after the end of the strategic tick control protocol was recorded. Tick counts and visual inspection were done weekly until days 203 and 119, respectively. The results showed that the adopted protocol was successful based on calculated efficacy. Mean efficacies from Day 7 to Day 119 were 86.1% and 96.1% for treated groups with low and high tick burdens, respectively, and mean tick count did not differ between them (P > 0.05) but did differ from their respectively controls (P = <0.0001). The use of spray formulation at the beginning of the protocol for animals with a high tick burden helped to avoid harmful tick infestations. Visual analysis of tick length anticipated the proposed treatment intervals. Treated groups remained without palliative treatment for 70 days, while control groups needed treatment every 28 days. It was concluded that strategic control protocols must be developed according to tick burden, and tick length can be used to indicate when treatment needs to be applied.

Entomopathogenic Fungi for Tick Control in Cattle Livestock From Mexico

Ticks are one of the main economic threats to the cattle industry worldwide affecting productivity, health and welfare. The need for alternative methods to control tick populations is prompted by the high prevalence of multiresistant tick strains to the main chemical acaricides and their ecological consequences. Biological control using entomopathogenic fungi (EPF) is one of the most promising alternative options. The objective of this paper is to review the use of EPF as an alternative control method against cattle ticks in Mexico. Metarhizium anisopliae sensu lato (s.l.) and Beauveria bassiana s.l. are the most studied EPF for the biological control of ticks in the laboratory and in the field, mainly against Rhipicephalus microplus; however, evaluations against other important cattle ticks such as Amblyomma mixtum and R. annulatus, are needed. A transdisciplinary approach is required to incorporate different types of tools, such as genomics, transcriptomics and proteomics in order to better understand the pathogenicity/virulence mechanism in EPF against ticks. Laboratory tests have demonstrated the EPF efficacy to control susceptible and resistant/multiresistant tick populations; whereas, field tests have shown satisfactory control efficiency of M. anisopliae s.l. against different stages of R. microplus when applied both on pasture and on cattle. Epidemiological aspects of ticks and environmental factors are considered as components that influence the acaricidal behavior of the EPF. Finally, considering all these aspects, some recommendations are proposed for the use of EPF in integrated control schemes for livestock ticks.

Efficacy of a water-based botanical acaricide formulation applied in portable spray box against the southern cattle tick, Rhipicephalus (Boophilus) microplus (Acari: Ixodidae), infesting cattle

Ectoparasitism result in annual losses to livestock producers estimated to reach billions of dollars in tropical and subtropical parts of the world where the southern cattle tick, Rhipicephalus (Boophilus) microplus, is established because this invasive pest is also a vector of pathogens causing bovine babesiosis and anaplasmosis. Reintroduction of R. microplus could be economically devastating for the cattle industry in the United States. Novel technologies are necessary to manage populations of R. microplus that are resistant to multiple classes of synthetic chemicals widely used as acaricides to control ticks infesting livestock, and to mitigate the environmental impact of these synthetic acaricides. Bioassays with a water-based formulation of a commercially available botanical acaricide (Essentria® IC3) at 6.25 % against a laboratory strain of R. microplus was 100 % lethal against unfed larvae, and 94 % mortality was recorded against engorged female ticks. These results prompted documentation of efficacy on infested cattle using an acaricide delivery system mimicking field conditions, which is required to consider the use of a product by integrated tick management programs. Twelve tick naïve cattle were artificially infested with unfed larvae on days -19, -12 and -5. On day -2, ticks from the left-side of the body of each animal were manually counted. Depending on pre-treatment tick counts the animals were assigned into three separate treatment groups: i) water (untreated control); ii) coumaphos 0.3 % in water (positive control); and iii) botanical acaricide 6.25 % in water. Five days after the last infestation, cattle were doused in a spray box and moved to individual stalls to collect tick data for calculation of treatment efficacy. The percentage control, based on the reproduction of surviving engorged female ticks after treatment with the 6.25 % Essentria in water-based spray was 70 % against R. microplus. Coumaphos treatment had a mean percent control of 100 %. Whereas this application of Essentria® IC3 cannot be recommended as a stand-alone method to eradicate R. microplus, the 6.25 % botanical acaricide water-based spray could be part of integrated tick management to control populations of R. microplus resistant to organophosphates like coumaphos and other classes of commercially available synthetic acaricides.

Effect of essential oils against acaricide-susceptible and acaricide-resistant Rhipicephalus ticks

The indiscriminate use of acaricides is a problem worldwide and has increased the selection of acaricide-resistant tick populations. The goal of this study was to evaluate the acaricide effects of two essential oils (from Schinus molle and Bulnesia sarmientoi) using the larval immersion test on three Rhipicephalus tick species. Rhipicephalus evertsi, Rhipicephalus appendiculatus and Rhipicephalus pulchelus ticks collected in Kenya, without history of acaricide exposure, were tested, as well as individuals from two populations of Rhipicephalus microplus (with or without history of acaricide exposure), for comparison. The sample most resistant to the treatments was a population of R. microplus with previous acaricide exposure, whereas the least tolerant sample was a strain of the same species that never had contact with acaricides (Porto Alegre strain). Interestingly, the field tick samples without previous acaricide exposure responded to essential oils with a mortality profile resembling that observed in the acaricide-resistant R. microplus field population, and not the susceptible Porto Alegre strain. The essential oil of B. sarmientoi and its two components tested (guaiol and bulnesol) caused the highest mortality rates in the tested species and are potential molecules for future studies on control methods against these species.

A retrospective review on ixodid tick resistance against synthetic acaricides: implications and perspectives for future resistance prevention and mitigation

The ending of the nineteenth-century was characterized by an escalation of ticks and tick-borne diseases that resulted in the death of many cattle. This necessitated the search for an effective means of tick control. Arsenicals were introduced in Australia in 1895, and arsenic-based dipping vats went on to be used for about 40 years until resistance was found in ticks and more effective alternatives - chemical acaricides - were developed after World War II. However, the development of resistance by ticks, environmental persistence, and mammalian toxicity militated against the sustained use of subsequent chemical acaricides. Furthermore, the development of resistance is a phenomenon that would always evolve, and the multiple mechanisms underlying the synthetic acaricides resistance are of great importance for future integrated control of ticks and tick-borne diseases. Hence, this study retrospectively reviewed the development of synthetic acaricides and the underlying mechanisms of tick resistance against synthetic acaricides in the hope of providing the implications and perspectives for resistance prevention and mitigation for future tick control.

Therapeutic equivalence of ivermectin 1% and two novel formulations combined of ivermectin 1% + fluazuron 12.5% for the control of Rhipicephalus (Boophilus) microplus in beef cattle from Uruguay

Background

Novel combinations of ivermectin (IVM) and fluazuron (FLU) are presented as an alternative for the control of ticks in cattle. Applying a combination of drugs with the aim to affect different stages of the parasite's life cycle is established as a potential measure to achieve the control of ticks in cattle.

Aim

To determine the therapeutic equivalence between two novel formulations of IVM 1% combined with FLU 12.5% tested on bovines naturally infested with Rhipicephalus (Boophilus) microplus.

Methods

Forty adult beef cattle were randomized into four groups (n = 10): IVM [1% (0.2 mg/kg)], combinations groups A and B [IVM 1% (0.2 mg/kg) + FLU 12.5% (2.5 mg/kg), each], and control [untreated]). On days 14, 27, and 49 after administration, the presence of ticks was ranked as null, low, medium, and high; a cumulative link model was adjusted to evaluate treatment response.

Results

Although all groups had some animals with the presence of ticks until day 27, on day 14 IVM [odds ratios (OR) 0.013, CI95%: 0.001-0.014, p < 0.01], A (OR 0.01, CI95%: 0.00-0.07, p < 0.01) and B (OR 0.01, CI95%: 0.00-0.148, p < 0.01) groups were different when compared to the control group, unlike on day 27 where only groups A (OR 0.02, CI95%: 0.00-0.17, p < 0.01) and B (OR 0.06, CI95%: 0.00-0.46, p < 0.01) remained different from the control group. On day 49 post-administration, IVM and B did not differ from the control group, with 0.95 probability (CI95% 0.92-1.02) of high parasite burden. At day 49 post-administration, group A was the only group free of ticks (OR 0.01, CI95%: 0.00-0.13, p < 0.01).

Conclusions

Pharmacotechnical differences in combined formulations should be considered in therapeutic equivalence studies.

Pictorial dissection guide and internal anatomy of the cattle tick, Rhipicephalus (Boophilus) microplus (Canestrini)

Ticks are pests and vectors of diseases that are of public health and veterinary importance. The cattle tick, Rhipicephalus microplus (Canestrini, 1888), is one of the most studied tick species because of its impact on livestock health and production in the tropical and subtropical parts of the world, costing the cattle industry billions annually. Control methods have evolved throughout the years but so has R. microplus. Reliance upon chemical control has created a consistent need to develop new technologies to overcome the pesticide resistance that occurs as the ticks adapt. In order to utilize the more advanced tools such as RNAi or Crispr/Cas9 systems, tick tissues need to be isolated and manipulated. Unfortunately, there are a limited number of dissection guides available providing a detailed view of tick internal anatomy. This manual includes photomicrographs to guide the dissection of R. microplus adults, male and female. Topography and anatomical differences between the internal organs of unfed and gravid adult females are described. We were able to locate the crucial tissues for cattle tick physiology and lay out spatial and temporal guidelines for their identification and dissection. Examples of how this information can be used at the nexus between organismal and molecular research to innovate tick control technologies is discussed.

Experimental Infection of Calves with Transfected Attenuated Babesia bovis Expressing the Rhipicephalus microplus Bm86 Antigen and eGFP Marker: Preliminary Studies towards a Dual Anti-Tick/Babesia Vaccine

Bovine babesiosis, caused by Babesia bovis and B. bigemina, is a major tick-borne disease of cattle with global economic impact. The disease can be prevented using integrated control measures including attenuated Babesia vaccines, babesicidal drugs, and tick control approaches. Vaccination of cattle with the Rhipicephalus microplus Bm86-based recombinant vaccine reduces the fitness of R. microplus and R. annulatus, but several booster inoculations are required to maintain protection. Herein, we generated a stable transfected strain of B. bovis expressing an enhanced GFP (eGFP) and a chimeric version of Bm86 (B. bovis/Bm86/eGFP). The eGFP was expressed in the parasite cytoplasm, whereas Bm86 was displayed on the surface of merozoites. Three splenectomized calves experimentally infected with B. bovis/Bm86/eGFP showed mild signs of acute disease and developed long-lasting antibody responses to B. bovis and native Bm86. No evidence of sequestration of parasites in the cerebral capillaries was found upon postmortem analysis, confirming attenuation of the strain. This is the first report of transfected B. bovis expressing the tick antigen Bm86 on the merozoite surface that elicits an antibody response to native Bm86. These results represent a proof of concept for a novel live, attenuated, tagged dual-vaccine approach to attempt simultaneous control of babesiosis and tick infestation.

Cytotoxic effects of Satureja montana L. essential oil on oocytes of engorged Rhipicephalus microplus female ticks (Acari: Ixodidae)

In addition to pesticidal activity, the capacity of natural compounds to inhibit the reproduction of parasites emerge as an important alternative tick control method. In this context, Satureja spp. stand out due to their recognized pesticidal properties. Among parasites of veterinary importance, the cattle tick, Rhipicephalus microplus, is responsible for great economic losses in livestock and transmission of relevant pathogens. Thus, the aim of this study was to evaluate the effects of different concentrations of the essential oil of Satureja montana L. on the ovary morphology of R. microplus engorged females through histological and histochemical techniques. The most remarkable morphological changes found were: cytoplasmic vacuolation of germ cells, irregular and thicker chorion, irregular oocyte shape, ring-shaped nucleolus, decrease in protein and carbohydrate content in oocytes, in addition to cellular changes in the oviduct and pedicel. All morphological changes were assessed using a semiquantitative method already established in the literature. Ticks exposed to 5.0 μl/ml of essential oil showed the most significant changes when compared to control groups. Thus, the essential oil of S. montana L. damaged the reproductive system of R. microplus, which may impair ticks' offspring production and promote a long-term control of this species. HIGHLIGHTS: The essential oil of Satureja montana L. affects the ovary morphology of the cattle tick. The main morphological alterations found were cytoplasmic vacuolation, irregular and thicker chorion and irregular oocyte shape. These alterations may impair the development of eggs.

Control of Rhipicephalus annulatus resistant to deltamethrin by spraying infested cattle with synergistic eucalyptus essential oil-thymol-deltamethrin combination

The current study investigated the synergistic effect of combinations containing deltamethrin (D), Eucalyptus essential oil (E), and the thyme essential oil component thymol (T), against a field population of Rhipicephalus annulatus in Egypt that was characterized to be resistant to D. Solutions of T, E, or TE at concentrations of 1.25-5% were combined with 5% deltamethrin at different dilutions (0.25-2 mL/L). Results of the adult immersion test used to estimate the in vitro acaricidal activity of these combinations at 5% yielded LC₅₀ values for D, E-D, T-D, and TE-D of 3.87 mL/L, 3.89 mL/L, 0.14 mL/L, and 0.05 mL/L, respectively. Biochemical analyses using whole-body homogenate of ticks from the in vitro tests revealed that the lowest acetylcholinesterase and glutathione peroxidase activity, and the maximum lipid peroxidation were recorded in ticks treated with 5% TE-D. Glutathione content significantly decreased (p ≤ 0.05) in all treated ticks. Three groups, each containing five cross breed cattle naturally infested with R. annulatus from the same area where resistance to D was detected, were sprayed twice at two-week intervals using 1 mL/L of 5% solutions of D, T-D, or TE-D. Overall efficacy of the D, T-D, and TE-D sprays by day 30 post-treatment was 21.6, 88.3, and 95 %, respectively. Ticks collected from infested cattle three days after treatment with the D spray deposited egg masses that were able to hatch, deposited small masses of eggs unable to hatch when exposed to the T-D spray, and laid few eggs that didn't hatch when sprayed with the TE-D combination. Values for liver and kidney function parameters were comparable in cattle before and after treatment with the combination sprays tested. The TE-D spray overcame the insensitivity to D of this R. annulatus population in Egypt, which also highlighted the significant synergistic effect of thymol on the acaricidal activity of deltamethrin observed in vitro. Acaricidal activity of the TE-D combination apparently has deleterious effects on multiple tick systems involving inhibition of acetylcholinesterase, increased lipid peroxidation, and oxidative stress. These findings document that combinations of natural and synthetic products can be part of integrated management solutions to the problem with widespread resistance to pyrethroids like deltamethrin in populations of cattle ticks, including R. annulatus, around the world.

Protecting dogs and cats against the Australian paralysis tick, Ixodes holocyclus (Acari: Ixodidae): A review of the Australian acaricide registration process

Tick control is mainly achieved through the use of effective ectoparasiticides that can be either dermally or systemically distributed in/on the host. Before any acaricide can be legally made available to veterinarians and pet owners, it must demonstrate efficacy in a series of well-designed dose confirmation studies. The data generated during these studies are then reviewed by government regulators and used for the registration of the acaricide. In Australia, the most significant tick species is the Australian paralysis tick, Ixodes holocyclus. This three-host tick produces a potent neurotoxin (holocyclotoxin) that induces a rapidly ascending flaccid paralysis that can be fatal to companion animals and larger mammals such as cattle and horses. The Australian Pesticides and Veterinary Medicines Authority (APVMA) is the national Australian regulator which sets the data requirements for the registration of acaricides. This paper reviews the requirements set by the APVMA and puts them in direct context with the biology, distribution and reported acaricide susceptibility of I. holocyclus. An overview of acaricides currently registered in Australia for the control of I. holocyclus in dogs and cats, their reported efficacy data and the conduct of I. holocyclus efficacy trials are also provided.

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A review of the requirements for the conduct of acaricide efficacy trials for Ixodes holocyclus was undertaken.

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The requirements of the Australian government regulator were put in direct context with the biology of the species.

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The need for the inclusion of Far North Queensland ticks into tick studies needs to be further assessed.

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At present, there is no evidence of acaricide resistance in Ixodes holocyclus.

Research on Integrated Management for Cattle Fever Ticks and Bovine Babesiosis in the United States and Mexico: Current Status and Opportunities for Binational Coordination

Bovine babesiosis is a reportable transboundary animal disease caused by Babesia bovis and Babesiabigemina in the Americas where these apicomplexan protozoa are transmitted by the invasive cattle fever ticks Rhipicephalus (Boophilus) microplus and Rhipicephalus(Boophilus) annulatus. In countries like Mexico where cattle fever ticks remain endemic, bovine babesiosis is detrimental to cattle health and results in a significant economic cost to the livestock industry. These cattle disease vectors continue to threaten the U.S. cattle industry despite their elimination through efforts of the Cattle Fever Tick Eradication Program. Mexico and the U.S. share a common interest in managing cattle fever ticks through their economically important binational cattle trade. Here, we report the outcomes of a meeting where stakeholders from Mexico and the U.S. representing the livestock and pharmaceutical industry, regulatory agencies, and research institutions gathered to discuss research and knowledge gaps requiring attention to advance progressive management strategies for bovine babesiosis and cattle fever ticks. Research recommendations and other actionable activities reflect commitment among meeting participants to seize opportunities for collaborative efforts. Addressing these research gaps is expected to yield scientific knowledge benefitting the interdependent livestock industries of Mexico and the U.S. through its translation into enhanced biosecurity against the economic and animal health impacts of bovine babesiosis and cattle fever ticks.

Cocktail Anti-Tick Vaccines: The Unforeseen Constraints and Approaches toward Enhanced Efficacies

Ticks are second to mosquitoes as vectors of disease. Ticks affect livestock industries in Asia, Africa and Australia at ~$1.13 billion USD per annum. For instance, 80% of the global cattle population is at risk of infestation by the Rhipicephalus microplus species-complex, which in 2016 was estimated to cause $22-30 billion USD annual losses. Although the management of tick populations mainly relies on the application of acaricides, this raises concerns due to tick resistance and accumulation of chemical residues in milk, meat, and the environment. To counteract acaricide-resistant tick populations, immunological tick control is regarded among the most promising sustainable strategies. Indeed, immense efforts have been devoted toward identifying tick vaccine antigens. Until now, Bm86-based vaccines have been the most effective under field conditions, but they have shown mixed success worldwide. Currently, of the two Bm86 vaccines commercialized in the 1990s (GavacTM in Cuba and TickGARDPLUSTM in Australia), only GavacTM is available. There is thus growing consensus that combining antigens could broaden the protection range and enhance the efficacies of tick vaccines. Yet, the anticipated outcomes have not been achieved under field conditions. Therefore, this review demystifies the potential limitations and proposes ways of sustaining enhanced cocktail tick vaccine efficacy.

Resistance of ticks on cattle to amitraz in Zimbabwe

Resistance of one host and three host ticks on cattle to amitraz was studied using samples from five diptanks in the Domboshawa Communal Land Area of Zimbabwe. A random tick profile and a questionnaire survey on the tick control practices of the area were also carried out. Engorged Rhipicephalus (Boophilus) decoloratus, Rhipicephalus appendiculatus and Amblyomma hebraeum females were randomly collected from cattle presented for dipping at the 5 diptanks and were allowed to oviposit separately at T: 28 °C and RH: 85-95%. Larvae obtained were tested for resistance against various amitraz concentrations (1-0.0078125%) using the Larval Packet Test (LPT) and were compared with susceptible reference strains of R. (B.) decoloratus (Makuti strain, 2017), R. appendiculatus (Lake Chivero strain, 2015) and A. hebraeum (Lake Mutirikwi strain, 2017). The most abundant tick species were R. (B.) decoloratus (27.2%), Hyalomma rufipes (20.0%), H. truncatum (16.0%), R. appendiculatus (12.0%) and R. evertsi evertsi (11.9%). Amblyomma hebraeum (8.6%) and A. variegatum (1.8%) were the least common in the collection; this suggests that they were not well established in Domboshawa. Low amitraz resistance (RL = I) was detected only in R. (B.) decoloratus at 2 of the 5 diptanks. In the future, decentralised tick control due to inadequate and inconsistent supply of acaricides could introduce a number of factors which could contribute towards resistance development.

Ticks and Tick-Borne Diseases in Cuba, Half a Century of Scientific Research

Ticks and the vast array of pathogens they transmit, including bacteria, viruses, protozoa, and helminths, constitute a growing burden for human and animal health worldwide. In Cuba, the major tropical island in the Caribbean, ticks are an important cause of vector-borne diseases affecting livestock production, pet animal health and, to a lesser extent, human health. The higher number of tick species in the country belong to the Argasidae family and, probably less known, is the presence of an autochthonous tick species in the island, Ixodes capromydis. Herein, we provide a comprehensive review of the ticks and tick-borne pathogens (TBPs) affecting animal and human health in Cuba. The review covers research results including ecophysiology of ticks, the epidemiology of TBPs, and the diagnostic tools used currently in the country for the surveillance of TBPs. We also introduce the programs implemented in the country for tick control and the biotechnology research applied to the development of anti-tick vaccines.

Botanical acaricides induced morphophysiological changes of reproductive and salivary glands in tick: A mini-review

Ticks are obligate hematophagous ectoparasites and important vectors of several pathogens of medical and veterinary significance, in addition to economic losses associated with their infestation. The primary method for the current control of tick is the use of synthetic acaricides, and many studies have focused on the tick control efficacy associated with the use of synthetic acaricides. However, the intensive use of these compounds has environmental and public health implications, in addition to the development of resistant tick populations. Over the years, studies have demonstrated the great potential of botanicals as an effective alternative in tick control. Most of the reviews on the acaricidal activity of botanicals focused on the effects relating to the development, reproduction, and mortality rate of ticks. Besides this acaricidal activity, botanicals can also affect the morphophysiology of the reproductive organs and the salivary glands that are important for tick procreation and survival. Effects relating to histopathological and cell ultra-structural alterations caused by botanical acaricides can be determined through microscopy techniques. Hence, the present mini-review focuses on studies dealing with morphophysiology changes of the reproductive system and the salivary gland of ticks exposed to botanical acaricides, with a view of expanding our knowledge for the future integrative application of botanical acaricides in tick control.

Acetylation of carvacrol raises its efficacy against engorged cattle ticks Rhipicephalus (Boophilus) microplus (Acari: Ixodidae)

The effects of acetylcarvacrol on the reproductive performance of engorged female R. microplus were evaluated. Carvacrol was acetylated by a reaction with acetic anhydride, confirmed by the identification of its melting point and by infrared spectroscopy. Based on the median lethal concentration, females were exposed to sublethal concentrations (3.7, 4.6 and 5.0 μL/mL) of acetylcarvacrol by means of the adult immersion test. The following parameters were evaluated: female weight before oviposition, pre-oviposition period, egg mass weight, egg production index, incubation period, hatching rate, fecundity rate, percentage of reduction in oviposition, percentage of reduction in hatching and product efficacy. The greatest efficacy was observed in the group treated with the highest concentration (91.69%) due to the greater weight reduction in egg mass (34.91 ± 0.02 mg) and the lower hatching rate (7.23 ± 15.50%). Therefore, this compound is a promising alternative for the control of R. microplus infestations.

In vitro acaricidal activity of Cymbopogon citratus, Cymbopogon nardus and Mentha arvensis against Rhipicephalus microplus (Acari: Ixodidae)

The chemical composition and acaricidal activity of plant-derived essential oils was assessed against Rhipicephalus microplus ticks. The essential oils of Mentha arvensis, Cymbopogon citratus and C. nardus were assessed for acaricidal activity against Rhipicephalus microplus. Essential oils (EO) of plants were separated by hydrodistillation (three times) and analyzed using gas chromatography - mass spectrometer (GC-MS). For bioassays, engorged females of R. microplus were exposed to C. citratus and C. nardus EO at 2%, 3%, 4% and 5% concentrations; and to M. arvensis EO at 1%, 3%, and 5% for 5 min. The weight egg mass, nutrient index (N.I), egg production index (E.P.I), hatching and control rate were evaluated. Non-feed larvae of R. microplus were exposed to essential oils with 0.25%, 0.5%; 1%; 1.5% and 2% concentrations; the mortality rate was measured after 48 h. Only engorged females presented reduced biological activities (oviposition, E.P.I) after exposure to M. arvensis at 3%, when in comparison to both positive and negative controls. The hatchability of R. microplus larvae ranged from 66.9% (after exposure to C. nardus EO at 5%) to 99.2% (positive control). The nutrition index was lower (46.6%) for the exposure to M. arvensis EO at 5%. M. arvensis at 3% and 5% concentrations was significantly efficient for engorged females when compared to control (53.7% and 47.5%, respectively). C. citratus EO at 1%, 1.5% and 2% concentrations yielded better results in the larval packet test, causing 100% mortality. Nonetheless, C. nardus and M. arvensis EO at 2% yielded 66% and 39% mortality, respectively. The study showed that M. arvensis presented potential for the control of R. microplus engorged females while C. citratus and C. nardus presented potential as a larvicide.

Toxicity, repellency and anti-cholinesterase activities of thymol-eucalyptus combinations against phenotypically resistant Rhipicephalus annulatus ticks

The current study was designed to compare the acaricidal activity of pure thymol (T) crystals, eucalyptus oil (E), and their combinations (T + E) at concentrations ranging from 0.625 to 10% against phenotypically deltamethrin-resistant Rhipicephalus annulatus ticks. The adulticidal, larvicidal, ovicidal, and repellent activities of the tested compounds and their possible mechanism of action were studied. Thymol showed 93.3% adulticidal activity at 10% concentration, whereas at 2.5% it achieved 100% larvicidal activity. Eucalyptus oil had a significant effect on tick adults at concentrations > 5%, and at 10% concentration it showed 96.7% adulticidal activity and stopped the egg hatching. On deltamethrin-resistant larvae, the median lethal concentration (LD₅₀) was 0.61, 7.5, and 0.61% for T, E, and T + E combinations, respectively, and repellent activities were 85.7, 62.5, and 100% at the 10% concentration used. Combinations of T + E did not induce additional effects as adulticidal and larvicidal in a comparison with T treatments. The tick's acetylcholinesterase significantly decreased as a result of all treatments including deltamethrin, whereas lipid peroxidation significantly increased compared with the control untreated ticks. The glutathione content significantly decreased as a result of all treatments except for treatments with 10% thymol and its combination with eucalyptus oil. Moreover, 10% eucalyptus oil significantly decreased the tick's glutathione peroxidase and catalase activities reflecting the attenuation of antioxidant defense in the ticks. In conclusion, thymol and eucalyptus oil showed excellent activities against deltamethrin-resistant R. annulatus isolates. Their action may be mediated via acetylcholinesterase inhibition. The effect of thymol-eucalyptus combinations recorded higher activities as an ovicidal and as a repellent.

Effects of the essential oil from Cymbopogon citratus on mortality and morphology of the tick Haemaphysalis longicornis (Acari: Ixodidae)

Haemaphysalis longicornis is one of the most prevalent tick species across eastern Asia, Australia, and New Zealand, and has been implicated as a vector of several pathogenic agents. This study evaluated the in vitro acaricidal efficacy of Cymbopogon citratus (lemongrass) essential oil on unfed H. longicornis using the adult and nymph immersion test, and the larval packet test. Six concentrations with three replications each of 10, 20, 30, 40, 50 and 60 mg/mL (adults and nymphs) were used, and 2.5, 5, 10, 20, 40 and 80 mg/mL (larvae), with control group (50% ethanol). The adult and nymph mortality rates were 98 and 100% at 50 mg/mL, and 95 and 100% at 60 mg/mL, respectively, whereas the larval mortality rate was 94 and 96% at 40 and 80 mg/mL, respectively. Mortality of adult, nymph and larva increased significantly in a dose-dependent manner. The LC₅₀ for adult, nymph, and larva, were 29.21 (95% confidence interval 25.90-32.58), 28.18 (23.78-32.25), and 28.06 (25.57-30.90) mg/mL, respectively. Scanning electron microscopy and light microscopy revealed a disjointed sensilla base from the sockets, cuticular cracks, blocked aeropyles, and shrinking of the midgut. These results showed that C. citratus essential oil could be a good eco-friendly alternative control strategy against ectoparasites like ticks due to its high acaricidal efficacy.

Botanical acaricides and repellents in tick control: current status and future directions

Ticks are obligate blood-sucking ectoparasites and notorious as vectors of a great diversity of, in many instances, zoonotic pathogens which can cause considerable damage to animal and human health. The most commonly used approach for the control of ticks is the application of synthetic acaricides. However, the negative impacts of synthetic acaricides on the treated animals and the environment, in addition to its documented role in the development of resistance has led to the search for safer and more environmentally friendly alternative methods without compromising efficacy. An emerging promising approach for the control of ticks which has attracted much attention in recent years is the use of botanicals. Indeed, botanicals have been widely reported to show diverse effects and great potential as tick repellent and control. Although several excellent reviews have previously focused on this topic, studies on the exploration and application of botanicals to control ticks have expanded rapidly. Herein, we provide an update on the current understanding and status of botanical acaricides and repellents in tick control using recently published articles between 2017 and 2019. We also discuss the challenges and future directions in the application of botanicals in tick control, with a view of providing important clues for designing new integrated tick control methods.

A family of serine protease inhibitors (serpins) and its expression profiles in the ovaries of Rhipicephalus haemaphysaloides

Serpins are evolutionarily conserved serine protease inhibitors found in many organisms. In arthropods, serpins are involved in feeding, development, oviposition, anti-coagulation and innate immune responses. We characterized of 11 serpins in the tick Rhipicephalus haemaphysaloides. These serpins have orthologous genes in other ticks, as indicated by phylogenetic analysis. Analysis of the reactive center loop and hinge regions of the protein sequences indicated that RHS7 encodes proteins that may lack proteinase inhibitor activity. All R. haemaphysaloides serpins had high amino acid sequence identities to Rhipicephalus microplus serpins. Tissue and temporal transcriptional profiling of eight R. haemaphysaloides serpins located in the ovaries demonstrated that they are transcribed during feeding and oviposition. These suggested their participation in the regulation of tick physiology. Immune serum from rabbits repeatedly infested with larvae, nymphs and adults of R. haemaphysaloides can recognize multiple recombinant serpins, respectively. After gene silencing, the blood feeding to repletion time was significantly longer and the 24 h attachment rate was significantly lower in the RHS3 and RHS7 knock down groups. The RHS9 and RHS11 silenced ticks had significant reduction in repletion time and egg-laying rate. Egg hatchability was significantly decreased in RHS4, RHS5 and RHS9 silenced ticks. All groups had significant reductions in engorged body weight. This study increases information on the serpins of R. haemaphysaloides and suggests that some RHSs are potential targets for development of tick vaccines.

Ectoparasites of Cattle

Diverse groups of ectoparasitic arthropods cause significant morbidity and mortality in most of the approximately 1.49 billion head of cattle worldwide. Hematophagous ectoparasites (ie, blood-feeding flies, myiasis-causing flies, lice, mites, ticks) are the most important in cattle. Intense use of ectoparasiticides to treat infestations can result in ectoparasite populations becoming resistant to this treatment method. Approaches integrating the use of different technologies are required to manage cattle ectoparasites effectively while addressing societal expectations regarding food safety and environmental health. Assessing the status of coparasitism with ectoparasites and endoparasites in cattle across agroecosystems is critical in advancing integrated parasite management.

The effect of breed, sex, and drug concentration on the pharmacokinetic profile of ivermectin in cattle

Ivermectin (IVM) is one of the most widely used antiparasitic drugs worldwide and has become the drug of choice for anthelmintic and tick treatment in beef cattle production. It is known that pharmacokinetic parameters are fundamental to the rational use of a drug and food safety and these parameters are influenced by different factors. The aim of this study was to evaluate the pharmacokinetic profile of IVM in Bos indicus, Bos taurus, and crossbreed cattle (B. indicus × B. taurus) kept under same field conditions and the possible impacts of sex and IVM formulation (1% and 3.15%). It was observed that IVM concentration was significantly affected by breed. The plasma concentrations of IVM, AUC, C_max , and t_1/2β were significantly higher in B. indicus compared to B. taurus. Crossbreed animals showed an intermediate profile between European and Indian cattle. No alteration in pharmacokinetics parameters was detected when comparing different gender. Concerning the pharmacokinetic data of IVM formulation, it was verified that T_max , AUC, and t_1/2β were higher in 3.15% IVM animals than those from 1% IVM formulation. The results clearly indicated that the IVM plasma concentrations in B. indicus were higher than that in B. taurus.

Evaluation of rotational grazing as a control strategy for Rhipicephalus microplus in a tropical region

Rhipicephalus microplus is the most significant tick of livestock and its control is particularly challenging due to its resistance to commercial acaricides. Pasture rotation is considered a management strategy that could help control R. microplus, however, the literature only contemplates mathematical models and little is known about the effects of this practice in the field. The objective of this work was to determine whether pasture rotation is an efficient method for controlling R. microplus. Two different experiments were performed that involved groups of continuous and rotational grazing bovines. Female ticks measuring 4.5-8.0 mm were counted on animals while larvae in pasture were counted using the flannel drag technique. Treatment for infested bovines was applied when the average group tick count was ≥30 females. The results showed that rotational grazing (with 20-day periods of rest) had a higher tick count on-host than continuous grazing (P < 0.05) and additional bovine treatment was needed. Sixty and 105 days were needed to re-infest and disinfest pasture of R. microplus larvae, respectively. The first treatment of bovines occurred 91 days after the animals were placed in a closed area. The results indicate that rotational grazing is not an efficient way to control R. microplus.

Morphometric similarity among populations of Rhipicephalus microplus (Acari: Ixodidae) in the north-western region of Colombia

Rhipicephalus microplus is one of the most widely distributed and economically important ticks able to transmit pathogens to vertebrate hosts which cause major constraints to public and livestock health. A better understanding of their population structure is crucial for the development of more effective control strategies. Modern morphometrics has enabled the quantification of size and shape variations to investigate population differences in anatomical structures. We therefore applied landmark-based and outline-based geometric morphometric approaches to study 85 field-collected adult females of three R. microplus Colombian populations along a distance of 28-67 km using the scutum and the basis capituli. Although size differences were found between some populations, mean shape and metric disparity of the analyzed structures were very similar, resulting in low classification scores (<41%). Thus, both structures support a metapopulation of R. microplus at a microgeographic level. The variance of shape between structures does not co-vary, likely indicating morphological modularity. These data provide first clues to understand the metric variation of R. microplus among natural populations from north-western Colombia.

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.

Management Options for Ixodes ricinus-Associated Pathogens: A Review of Prevention Strategies

Ticks are important human and animal parasites and vectors of many infectious disease agents. Control of tick activity is an effective tool to reduce the risk of contracting tick-transmitted diseases. The castor bean tick (Ixodes ricinus) is the most common tick species in Europe. It is also a vector of the causative agents of Lyme borreliosis and tick-borne encephalitis, which are two of the most important arthropod-borne diseases in Europe. In recent years, increases in tick activity and incidence of tick-borne diseases have been observed in many European countries. These increases are linked to many ecological and anthropogenic factors such as landscape management, climate change, animal migration, and increased popularity of outdoor activities or changes in land usage. Tick activity is driven by many biotic and abiotic factors, some of which can be effectively managed to decrease risk of tick bites. In the USA, recommendations for landscape management, tick host control, and tick chemical control are well-defined for the applied purpose of reducing tick presence on private property. In Europe, where fewer studies have assessed tick management strategies, the similarity in ecological factors influencing vector presence suggests that approaches that work in USA may also be applicable. In this article we review key factors driving the tick exposure risk in Europe to select those most conducive to management for decreased tick-associated risk.

A serpin from the tick Rhipicephalus haemaphysaloides: Involvement in vitellogenesis

Tick serpins are involved in enzyme activity, food digestion, blood-feeding, immune response and anticoagulation. Little is known about the potential roles of serpins in tick reproduction. RHS8, a serpin from the tick Rhipicephalus haemaphysaloides, has an open reading frame 1212 bp long and encodes a protein that has 404 amino acids and a predicted molecular weight of 45 kDa. RHS8 exhibits 89.58 % amino acid identity with RmS15 in Rhipicephalus microplus. RHS8 was expressed primarily in larvae and nymphs. RHS8 mRNA expression in the ovaries, fat bodies and salivary glands were up-regulated from feeding to ovipositing ticks. RNAi results showed that RHS8 dsRNA-injected ticks had a lower body weight, longer feeding time, fewer eggs laid and lower egg hatchability. Tick reproduction, such as egg laying and hatching, was disrupted by RNAi. Compared with the control group, ovaries of the RHS8 interference group were light brown color, indicating a reduction in yolk granule accumulation. Western blot results showed that the expression of RHVg3 and RHVg4 proteins in ovaries was reduced in the RHS8 dsRNA-injected group. These results indicate that RHS8 is related to tick reproduction and its interference affects vitellogenesis.

Tick Cell Lines in Research on Tick Control

Ticks and the diseases they transmit are of huge veterinary, medical and economic importance worldwide. Control of ticks attacking livestock and companion animals is achieved primarily by application of chemical or plant-based acaricides. However, ticks can rapidly develop resistance to any new product brought onto the market, necessitating an ongoing search for novel active compounds and alternative approaches to tick control. Many aspects of tick and tick-borne pathogen research have been facilitated by the application of continuous cell lines derived from some of the most economically important tick species. These include cell lines derived from acaricide-susceptible and resistant ticks, cell sub-lines with in vitro-generated acaricide resistance, and genetically modified tick cells. Although not a replacement for the whole organism, tick cell lines enable studies at the cellular and molecular level and provide a more accessible, more ethical and less expensive in vitro alternative to in vivo tick feeding experiments. Here we review the role played by tick cell lines in studies on acaricide resistance, mode-of-action of acaricides, identification of potential novel control targets through better understanding of tick metabolism, and anti-tick vaccine development, that may lead to new approaches to control ticks and tick-borne diseases.

Rhipicephalus microplus cystatin as a potential cross-protective tick vaccine against Rhipicephalus appendiculatus

Rhipicephalus appendiculatus, the brown ear tick, is an important disease vector of livestock in eastern, central and southern Africa. Rhipicephalus appendiculatus acaricide resistance requires the search for alternative methods for its control. Cystatins constitute a superfamily of cysteine peptidase inhibitors vital for tick blood feeding and development. These inhibitors were proposed as antigens in anti-tick vaccines. In this work, we applied structural and biochemical approaches to characterize a new cystatin named R. appendiculatus cystatin 2a (Racys2a). Structural modeling showed that this new protein possesses characteristic type 2 cystatin motifs, besides conservation of other structural patterns along the protein. Peptidase inhibitory assays with recombinant Racys2a showed modulation of tick and host cathepsins involved in blood digestion and immune system responses, respectively. A heterologous tick challenge with R. appendiculatus in rabbits immunized with recombinant Rhipicephalus microplus cystatin 2c (rBmcys2c) was performed to determine cross-reactivity. Histological staining showed that rBmcys2c vaccination caused damage to the gut, salivary gland and ovary tissues in R. appendiculatus. Furthermore, cystatin vaccine reduced the number of fully engorged adult females in 11.5 %. Consequently, strategies to increase the protection rate are necessary, including the selection of two or more antigens to compose a vaccine cocktail.

Network analysis uncovers putative genes affecting resistance to tick infestation in Braford cattle skin

Background

Genetic resistance in cattle is considered a suitable way to control tick burden and its consequent losses for livestock production. Exploring tick-resistant (R) and tick-susceptible (S) hosts, we investigated the genetic mechanisms underlying the variation of Braford resistance to tick infestation. Skin biopsies from four-times-artificially infested R (n = 20) and S (n = 19) hosts, obtained before the first and 24 h after the fourth tick infestation were submitted to RNA-Sequencing. Differential gene expression, functional enrichment, and network analysis were performed to identify genetic pathways and transcription factors (TFs) affecting host resistance.

Results

Intergroup comparisons of hosts before (Rpre vs. Spre) and after (Rpost vs. Spost) tick infestation found 51 differentially expressed genes (DEGs), of which almost all presented high variation (TopDEGs), and 38 were redundant genes. Gene expression was consistently different between R and S hosts, suggesting the existence of specific anti-tick mechanisms. In the intragroup comparisons, Rpost vs. Rpre and Spost vs. Spre, we found more than two thousand DEGs in response to tick infestation in both resistance groups. Redundant and non-redundant TopDEGs with potential anti-tick functions suggested a role in the development of different levels of resistance within the same breed. Leukocyte chemotaxis was over-represented in both hosts, whereas skin degradation and remodeling were only found in TopDEGs from R hosts. Also, these genes indicated the participation of cytokines, such as IL6 and IL22, and the activation of Wingless (WNT)-signaling pathway. A central gene of this pathway, WNT7A, was consistently modulated when hosts were compared. Moreover, the findings based on a genome-wide association study (GWAS) corroborate the prediction of the WNT-signaling pathway as a candidate mechanism of resistance. The regulation of immune response was the most relevant pathway predicted for S hosts. Members of Ap1 and NF-kB families were the most relevant TFs predicted for R and S, respectively.

Conclusion

This work provides indications of genetic mechanisms presented by Braford cattle with different levels of resistance in response to tick infestation, contributing to the search of candidate genes for tick resistance in bovine.