Evidence of multiple mechanisms of alphacypermethrin and deltamethrin resistance in ticks Rhipicephalus microplus in Benin, West Africa

Genetic Diversity of Rhipicephalus (Boophilus) microplus for a Global Scenario: A Comprehensive Review

Rhipicephalus microplus poses a substantial threat to livestock health and agricultural economies worldwide. Its remarkable adaptability to diverse environments and hosts is a testament to its extensive genetic diversity. This review delves into the genetic diversity of R. microplus, employing three pivotal genetic markers: the cytochrome c oxidase I (COX1) gene, ribosomal genes, and microsatellites. The COX1 gene, a crucial tool for genetic characterization and phylogenetic clustering, provides insights into the adaptability of ticks. Ribosomal genes, such as internal transcribed spacer regions (ITS-1 and2) as well as 18S and 28S, are routinely utilized for species differentiation. However, their use is limited due to indels (insertions and deletions). Microsatellites and minisatellites, known for their high polymorphism, have been successfully employed to study populations and genetic diversity across various tick species. Despite their effectiveness, challenges such as null alleles and marker variations warrant careful consideration. Bm86, a well-studied vaccine candidate, exhibits substantial genetic diversity. This diversity directly influences vaccine efficacy, posing challenges for developing a universally effective Bm86-based vaccine. Moreover, the review emphasizes the prevalence of genes associated with synthetic pyrethroid resistance. Identifying single nucleotide polymorphisms in the acaricide-resistant genes of R. microplus has facilitated the development of molecular markers for detecting and monitoring resistance against synthetic pyrethroids. However, mutations in sodium channels, the target site for synthetic pyrethroid, correlate well with the resistance status of R. microplus, which is not the case with other acaricide target genes. This study underscores the importance of understanding genetic diversity in developing effective tick management strategies. The choice of genetic marker should be tailored based on the level of taxonomic resolution and the group of ticks under investigation. A holistic approach combining multiple markers and integrating additional molecular and morphological data may offer a more comprehensive understanding of tick diversity and relationships. This research has far-reaching implications in formulating breeding programs and the development of vaccine against ticks and tick-borne diseases (TTBDs) as well as strategies for the management of resistant ticks.

Widespread acaricide resistance and multi-resistance in Rhipicephalus microplus in Ecuador and associated environmental and management risk factors

Rhipicephalus microplus is a cattle tick widely distributed in tropical and subtropical areas. Various acaricides are used and applied to control the ticks, but resistance is common. The objectives of this study were to evaluate the spatial distribution of resistance to the most commonly applied acaricides (amitraz, ivermectin, and alpha-cypermethrin) in ticks and assess potential risk factors associated with tick resistance in a strip between ±0.5° latitude of the continental part of Ecuador. Larval package tests were used to evaluate the level of acaricide resistance in 96 cattle farms. The association between 11 farm management and 8 ecological variables and acaricide resistance and multi-resistance was evaluated. Dose-response models were used to study the level of resistance. 72 % (69/96), 70 % (67/96), and 64 % (61/96) of farms had ticks resistant to amitraz, ivermectin, and alpha-cypermethrin, respectively. Multi-resistance was also widespread. Larger herds and dairy farms had a significantly higher probability of resistance for three commonly used acaricides. Environmental factors related to rainfall were also associated with acaricidal resistance presence. Ivermectin resistance was associated with use of the acaricide (OR = 8.9909; 7.7519-10.2300), mean temperature (OR = 1.3205;1.0742-1.6799)), and inversely associated with paddock rotation (OR = 0.1753; 0.0294-0.7836), and precipitation of the wettest month (BIO13) (OR = 0.9903; 0.9839-0.9957); amitraz with use of the acaricide (OR = 4.3934; 3.3679-5.4188), precipitation seasonality (BIO15) (OR=0.9742; 0.9542-0.9925), and precipitation (OR = 0.9995; 0.9994-0.9999); and alpha-cypermethrin with precipitation (OR=0.9995; 0.9990-0.9999) and use of the acaricide (OR = 14.4597; 13.4343-15.4852). In conclusion, acaricide resistance was widespread in our study area. Better-integrated tick management and environmentally friendly control strategies are required to reduce the use of acaricides while limiting tick-associated damage in herds.

Acaricide Resistance Development in Rhipicephalus (Boophilus) microplus (Acari: Ixodidae) Populations against Amitraz and Deltamethrin on Communal Farms of the King Sabata Dalindyebo Municipality, South Africa

Chemical acaricides are widely used to control ticks and tick-borne pathogens in cattle. However, prolonged and indiscriminate use of these chemicals inevitably leads to the selection of resistant ticks. In-vitro bioassays (adult and larval immersion tests) were conducted to assess amitraz and deltamethrin resistance in Rhipicephalus (Boophilus) microplus populations from communal farms of the King Sabata Dalindyebo municipality of South Africa. Data generated on percentage inhibition of oviposition (%IO) revealed that all the tick populations assessed showed resistance (%IO ≤ 95%) to at least one of the acaricides. All six tick populations assessed for efficacy (%IO ≥ 95%) at the DD) with deltamethrin were resistant (%IO ≤ 95%) and only one of the six tick populations assessed for efficacy with amitraz was susceptible. Based on the resistance ratios (RR), the adult immersion test detected amitraz and deltamethrin resistance in three (RR ranging from 2.30 to 3.21) and five (RR ranging from 4.10 to 14.59) of the six tick populations, respectively. With the larval immersion test, deltamethrin and amitraz resistance (larval mortality < 90% at the DD) was detected in all four and three of four R. (B.) microplus populations assessed, respectively. These data are critical for the design of an effective and sustainable tick control strategy on the communal farms.

Geographical distribution of hard ticks (Acari:Ixodidae) and tick-host associations in Benin, Burkina-Faso, Ivory-Coast and Togo

Knowledge of ticks and associated pathogens is crucial to assess the risk of exposure of humans and animals to pathogens. For this review, we collected relevant data from published articles and field collections to provide an update on the biodiversity of ticks, and tick-host associations in four countries of West Africa: Benin, Burkina-Faso, Ivory-Coast, and Togo. The literature review was done according to Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. The search was limited to literature published from 1953 to 2021 in English and French sources. Out of 104 articles retrieved, only 41 studies met the eligibility criteria and were included in the review. The final database included a total of 53,619 adults, nymphs and larval ticks belonging to 24 species and five genera (Amblyomma, Haemaphysalis, Hyalomma, Ixodes and Rhipicephalus) that were collected from 23 different species of wild and domestic animals. This is the first record of Ixodes aulacodi and Rhipicephalus simpsoni in Benin, together with two new host records for A. latum. This checklist allows an update on tick-host associations and provides information on the diversity of ticks in West Africa.

Development of acaricide resistance in tick populations of cattle: A systematic review and meta-analysis

The development of acaricide resistance in ticks infesting cattle is a major problem in the livestock industry in tropical and subtropical regions worldwide. To determine the current global trends and prevalence of acaricide resistance development (ARD) in tick populations of cattle, a systematic review and meta-analysis with an emphasis on Rhipicephalus (Boophilus) microplus was conducted. Data searches from five English electronic databases yielded 88 journal articles published between 1992 and 2020. In total, 218 in - vitro bioassays were used to investigate 3939 tick populations of cattle; of these, the 57.6% that exhibited ARD were largely limited to South America (Brazil), Central America (Mexico), and Asia (India). A total of 3391 of these tick populations were R. (B.) microplus, of which 2013 exhibited ARD. Random effects meta-analyses indicated that the exhibition of ARD was higher in R. (B.) microplus (66.2%) than in other tick species. Global prevalence estimates of ARD in R. (B.) microplus vary as a function of geography, detection methods, and acaricide compounds. In general, high heterogeneity was noted among the studies. However, homogeneity was observed among studies from India, suggesting the establishment of acaricide resistance in Indian R. (B.) microplus populations. Current tick control interventions are urgently required to limit the evolution and implications of resistance development.

Phenotypic and genotypic characterization of dog tick Rhipicephalus sanguineus sensu lato (Acari: Ixodidae) resistance to deltamethrin in Benin

The aim of this study was to evaluate the phenotypic and genotypic resistance of Rhipicephalus sanguineus sensu lato to deltamethrin in dogs in the municipality of Natitingou in Benin. In this study, the collection and identification of ticks, Larval Packet Test and specific allele PCR were the main methods used. A total of 41 dogs were examined and 420 ticks were collected in six areas which includes: Tchrimina, Yokossi, Boriyoure, Berécingou, Péporiyakou and Perma. Three species of ticks were identified and they include: R. sanguineus s.l., Rhipicephalus microplus and Haemaphysalis spp. However, R. sanguineus s.l. was the most abundant tick species (9.85) and had the highest parasitic intensity (10.36). The results of the Larval Packet Test showed that the larvae of R. sanguineus s.l. developed a phenotypic resistance against deltamethrin, particularly in the Bérécingou area where resistance ratios of LC50 and LC95 of R. sanguineus s.l. compared to a susceptible strain were 1.591 (1.025-3.054) and 65.339 (20.235-579.825) respectively. The molecular study of the sodium channel gene revealed three genotypes namely the susceptible genotype (SS), the heterozygous genotype (SR) and the resistant genotype (RR), which correlates with the phenotypic results. This information is fundamental to improve monitoring and resistance management strategies of R. sanguineus s.l. ticks to pyrethroids.

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.

A Survey of Potentially Pathogenic-Incriminated Arthropod Vectors of Health Concern in Botswana

Arthropod vectors play a crucial role in the transmission of many debilitating infections, causing significant morbidity and mortality globally. Despite the economic significance of arthropods to public health, public knowledge on vector biology, ecology and taxonomic status remains anecdotal and largely unexplored. The present study surveyed knowledge gaps regarding the biology and ecology of arthropod vectors in communities of Botswana, across all districts. Results showed that communities are largely aware of individual arthropod vectors; however, their 'potential contribution' in disease transmission in humans, livestock and wildlife could not be fully attested. As such, their knowledge was largely limited with regards to some aspects of vector biology, ecology and control. Communities were strongly concerned about the burden of mosquitoes, cockroaches, flies and ticks, with the least concerns about fleas, bedbugs and lice, although the same communities did not know of specific diseases potentially vectored by these arthropods. Knowledge on arthropod vector control was mainly limited to synthetic chemical pesticides for most respondents, regardless of their location. The limited knowledge on potentially pathogen-incriminated arthropod vectors reported here has large implications for bridging knowledge gaps on the bio-ecology of these vectors countrywide. This is potentially useful in reducing the local burden of associated diseases and preventing the risk of emerging and re-emerging infectious diseases under global change.

Molecular survey of pyrethroid and fipronil resistance in isolates of Rhipicephalus microplus in the north of Uruguay

The resistance of Rhipicephalus microplus to acaricides is a serious control problem, so its early diagnosis by a molecular technique is important. This study aims to develop a multiplex allele-specific polymerase chain reaction (PCR) for single-nucleotide polymorphisms (SNPs) in the para-sodium channel gene and in the GABA-Cl gene, associated with pyrethroids (cypermethrin and flumethrin) and fipronil resistance, respectively. We used 22 tick field isolates from farms with tick control problems (sampling convenience). These farms are located in departments of northern Uruguay. Three mutations in the sodium channel gene (Domain II S4-5: C190A and G215T; domain III S6: T2134A) and one in the GABA-Cl gene (A286S/L: CG856CC/TG) were studied. Mutations G215T and T213A were not detected. In all field isolates, the resistant allele (R) for C190A mutation (knockdown resistance, kdr) was detected, mainly in heterozygous individuals (SR) (11.1% to 86.7%). The highest incidence of the kdr mutant allele occurred in the Tacuarembó tick field isolates, where on 7 out of 10 farms >30% of individuals were SR and on one farm > 30% of individuals were RR. The next highest was Artigas (half of farms had>30% SR individuals and a quarter had >30% RR individuals). The resistance to dieldrin locus (rdl) mutation (CG856CC/TG) was absent in five field isolates. The highest incidenceof the mutant allele was observed in ticks from farms in Rivera (all farms had SR in >30% of individuals and two farms had RR in >12.5 and >16.7% of individuals) followed by farms in Tacuarembó (3 of 10 farms had >30% SR and 2 with >30% RR). Less than half of the farms had rdl in homozygous individuals. No significant association was observed between phenotypic bioassays and the rdl resistance allele. Several field isolates were phenotypically susceptible to the presence of the rdl allele. Several causes are possible (bioassay sensitivity, discriminating concentration). Individuals with simultaneous kdr and rdl mutations were present in 17 field isolates, and their frequency varied between 0.06% and 60%. Genotypic analysis shows that tick resistance to both acaricides, especially pyrethroids, is a serious problem. It is important to monitor the resistance using molecular techniques to plan efficient control measures. This is the first report describing kdr and rdl detection in R. microplus in Uruguay.

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.

Detection of single nucleotide polymorphism in the para-sodium channel gene of Rhipicephalus annulatus populations from Egypt resistant to deltamethrin

Rhipicephalus annulatus field populations collected from small cattle farms in Beni-Suef province in Egypt were evaluated for deltamethrin resistance by toxicological in vitro bioassays (adult immersion test-AIT and larval packet test-LPT). Moreover, a quantitative PCR high resolution melting (PCR-HRM) technique was used to detect nucleotide substitutions in the voltage-gated sodium channel (Na-channel) gene. By the in vitro bioassays, the examined ticks were phenotypically categorized as deltamethrin susceptible (populations El-Wasta - A, and El-Hakamna - C) or resistant (populations El-Wasta - B, El-Hakamna - D, EL-Halabia - E, and Kom-abokhalad - F). Based on LPT findings, the phenotypic resistant populations were found to have a resistance ratio between 6.5 - 10.8. The PCR-HRM genotyping of the ticks showed variable melting curves among the populations in domain II of the Na-channel gene. Analysis of the curves showed the presence of wild type, mutant homozygous, and mutant heterozygous tick individuals. By sequencing the PCR amplified fragments, the C190A mutation was the only detected nucleotide polymorphism of domain II among the phenotypically resistant populations, which was present in 39.5 % (34/86) of the ticks tested. On the other hand, the phenotypically susceptible populations A and C did not show C190A mutant homozygous (RR) individuals. Meanwhile, in domain III all of the examined populations revealed melting curves like the wild type. Furthermore, the sequence analysis of these populations confirmed the absence of SNPs in domain III. The C190A single point mutation was detected for the first time in domain II of the Na-channel gene of deltamethrin-resistant R. annulatus in Egypt using PCR-HRM. Screening for efficacy of chemical compounds used by farmers to control ticks on cattle should be considered as part of animal health programs to manage the emerging resistance to acaricides in R. annulatus populations.

Standardization of tick specific biochemical tools for estimation of esterases, monooxygenases and glutathione S-transferase for characterization of acaricide resistance

Protocols to determine metabolic resistance in ticks were mainly derived from reports published using mosquitoes and agriculturally important insects without prior standardization. In the present study, biochemical assays were standardized to quantify acaricide metabolizing enzymes in tick homogenates. Three variables viz., age, number of larvae and reaction time were optimized using reference susceptible IVRI-I and deltamethrin resistant IVRI-IV (Resistance Factor = 194) tick strains. The optimum conditions for estimation of general esterases were 10-15 day old 40 larvae with 15 mins reaction time, 15-20 day old 40 larvae with 20 mins reaction time for Glutathione S- transferase, while 10-15 day old 80 larvae with 5 mins reaction time for monooxygenase. The standardized protocols were further validated in multi acaricide resistant strain (IVRI-V) and in nine field isolates having variable resistant factors to different acaricides. In all the nine heterogeneous field isolates, a significant correlation (p < .05) between resistance to synthetic pyrethroids and over-expression of esterases and monooxygenase was noticed. Similarly, esterases and GST activities were significantly correlated with resistance to organophosphates. The details of the assay protocol are explained for adoption in different laboratories.

Resistance profile and molecular characterization of pyrethroid resistance in a Rhipicephalus microplus strain from Colombia

Intensive use of chemical acaricides for the control of cattle ticks (Rhipicephalus microplus) has led to the development of multiple acaricide resistance in Colombia. The present study aimed to characterize, using toxicological bioassays and molecular biology techniques, the resistance profile of a tick strain isolated from the Arauca state, Northeast Colombia. Commercial acaricides were used in adult immersion tests to determine its in vitro efficacies. Deltamethrin showed very low activity (4-7.3%), a mixture of cypermethrin and chlorpyrifos had intermediate efficacy (64-75.2%), and ethion presented the highest activity (88.5-100%). A colony (Arauquita strain) was established and larval immersion tests confirmed high resistance level to deltamethrin (241-fold) and susceptibility to ivermectin. A quantitative polymerase chain reaction-high resolution melt technique was used to identify single nucleotide polymorphisms (SNPs) in the para-sodium channel gene. All of the genotyped individuals were mutant, presenting one (n = 7), two (n = 7) or three (n = 9) SNPs previously associated with pyrethroid resistance. Sequencing revealed a novel mutation (F712L), that was found for the first time in R. microplus ticks from South America. This is the first description of mutations associated with pyrethroid resistance in R. microplus from Colombia. The acaricide resistance pattern found in the Arauquita strain is similar to other parts of Colombia.

Voltage-gated sodium channel gene mutations and pyrethroid resistance in Rhipicephalus microplus

Pyrethroid pesticides are extensively used to manage animal and human disease vectors including the southern cattle tick Rhipicephalus microplus (Canestrini). The indiscriminate and incorrect use of pyrethroids has led to the almost ubiquitous development of resistance to this pesticide class for this tick species. Voltage-gated sodium channels (Na-channels) are the primary target-site of pyrethroids and several studies on the involvement of mutations in the coding gene among pyrethroid-resistant R. microplus populations from different parts of the world have shown that there are various single nucleotide polymorphisms (SNPs) that are associated with resistance to pyrethroids. Identification of the exact location of the mutations in the protein coding regions of the targeted gene facilitates the design of various molecular tools for genotyping the resistant populations and thus promotes the rapid detection of resistance. This review aims to provide an update on the identification of pyrethroid resistance-associated Na-channel mutations from R. microplus.The database of diverse mutations from different regions of the world helped us to develop the molecular markers for resistance monitoring in a rapid and efficient manner. Their role and the development of different forms of molecular tools for genotyping ticks for mutations in the Na-channel gene are also discussed. In this review, the word mutation is used interchangeably with SNP.

Partial characterization of the voltage-gated sodium channel gene and molecular detection of permethrin resistance in Rhipicephalus annulatus (Say, 1821)

The cattle tick, Rhipicephalus annulatus (Say) is a vector of bovine babesiosis and responsible for direct and indirect losses to cattle producing areas located in temperate and subtropical dry regions. Resistance against pyrethroids has been reported for this species in Asia and Africa, but never before in North America. An outbreak strain, Rio Lado, collected close to the border between Mexico and the United States, in Maverick County, Texas, showed low level of resistance to permethrin, a pyrethroid pesticide. We used genomic material from different strains of cattle ticks collected within the Permanent Quarantine Zone (Rio Lado, Vega and Klein Grass strains) to partially characterize the coding gene of the voltage-gated sodium channel (Na-channel), target-site of pyrethroid pesticides, and search for putative mutations associated with resistance using quantitative PCR high resolution melt (HRM) analysis. The two amplified fragments, corresponding to domains II and III of the Na-channel, were 100 % identical to its ortholog in Rhipicephalus microplus (Canestrini). No nucleotide polymorphisms in the Na-channel gene were observed in the pyrethroid-resistant Rio Lado strain, when compared to the susceptible strains Klein Grass and Vega. This study reports the first case of pyrethroid resistance in R. annulatus collected in the United States. Also, we provide new genomic data for this species of tick that allows for the development of a new method to screen for mutations associated with pyrethroid resistance.

Menace of acaricide resistance in cattle tick, Rhipicephalus microplus in India: Status and possible mitigation strategies

Livestock in general and dairy sector in particular plays a vital role in the Indian economy and in the socio-economic development of millions of people. Rhipicephalus microplus, a one-host and the most prevalent cattle tick in various agro climatic zones of India. This tick species is responsible for severe economic losses to livestock owners both through the direct effects of blood sucking, injection of toxins and indirectly by transmitting pathogens. Due to inadvertent and indiscriminate use of chemicals to kill ticks, field tick population has developed resistance to almost all chemicals that are used to manage them. The intention of this review is to provide the current status of resistance in ticks, the possible mechanisms of resistance operating in the tick population, factors contributing to the development of resistance and the managemental strategies.

Molecular markers and their application in the monitoring of acaricide resistance in Rhipicephalus microplus

Monitoring acaricide resistance and understanding the underlying mechanisms are critically important in developing strategies for resistance management and tick control. Identification of single nucleotide polymorphisms in the acaricide-resistant associated gene of Rhipicephalus microplus has enabled the development of molecular markers for detection and monitoring of resistance against different types of acaricide. There are many molecular markers developed for resistance monitoring, including mutations on target genes such as sodium channel, acetylcholinesterase, carboxylesterase, β-adrenergic octopamine receptor, octopamine-tyramine etc. Molecular genotyping through molecular markers can detect the presence of resistance-associated genes in a tick population before it reaches high frequency. This review aims to provide an update on the various molecular markers discovered to date from different regions of the world.

Molecular evidence for the inhibition of cytochrome p450s and cholinesterases in ticks by the repellent DEET

For more than 50 years DEET (N,N-Diethyl-m-toluamide) has been considered the gold standard of repellents. It is applied to the skin or clothing to deter mosquitoes and other blood-sucking invertebrate pests from approaching and/or settling, and ultimately it provides temporary protection from bites. Despite rampant global use, surprisingly little is understood about DEET's mode of action and the molecular targets of the active ingredient. Furthermore, the theories into its mechanism for repellency are largely based off fruit fly and mosquito research. Since ticks possess a unique sensory structure, the Haller's organ, the specific genes and pathways associated with DEET avoidance may differ from insects. In these studies, we collected American dog ticks (Dermacentor variabilis) from four natural populations within Manitoba, Canada. We first carried out behavior assays, which showed DEET effectively repelled the ticks. RNA sequencing revealed that DEET caused a rapid and substantial reduction in the abundance of transcripts encoding cytochrome P450 and acetylcholinesterase genes, which gradually recovered over the 24 h time course. Finally, enzymatic kinetics provided functional support for DEET's role as an effective inhibitor of P450 s. While many facets of its mode of action remain to be worked out, our study provides valuable insights into the molecular underpinnings of DEET's repellence in ticks.