Acaricide effect of plants from the Brazilian savanna on a population of Rhipicephalus microplus with phenotypic resistance to cypermethrin and trichlorfon.

Rhipicephalus microplus is among the most important ectoparasites for livestock. The use of synthetic acaricides has raised some concerns due to the selection of tick populations that are resistant to acaricides and environmental contamination. Therefore, plant extracts have been used as alternatives for the treatment of animals infested with ticks. In this study, R. microplus populations from seven different dairy farms were collected and assessed for their resistance to the acaricides cypermethrin or trichlorfon. Larvae of the most resistant population were used in assays to evaluate the acaricide effect of leaf extracts from plants of the Brazilian savanna. The most active extracts were also tested against fully engorged females. Among seven tick populations, five and three showed resistance level ≥ III for cypermethrin or trichlorfon, respectively. The most resistant tick population was evaluated in mortality assays with the plants Piptadenia viridiflora, Annona crassiflora, Caryocar brasiliense, Ximenia americana, and Schinopsis brasilienses. The ethanolic extracts of C. brasiliense, X. americana and S. brasilienses showed higher larvicidal effects in comparison to the other extracts and cypermethrin. The ethanolic extract of X. americana showed 60.79 % efficacy against fully engorged females of the acaricide resistant tick strain. The ethanolic extracts of C. brasiliense, X. americana, and S. brasilienses showed peaks in HPLC-DAD, indicating the presence of tannins and flavonoids. Three of the plants showed promising results and should be explored in further studies to develop novel tools to control R. microplus in cattle.

Drivers and evolution of acaricide resistance and multi-resistance in two Ecuador's subtropical livestock farming areas.

The management of cattle ticks, particularly Rhipicephalus microplus, poses a global challenge in subtropical regions like Ecuador due to its impact on meat and milk productivity, leading to economic losses. Misuse of acaricides has resulted in resistance and multi-resistance, diminishing their effectiveness. This study evaluated resistance to amitraz, alpha-cypermethrin, and ivermectin using the Larval Packet test, laboratory-reared tick larvae collected from cattle were tested. Data on farm management and tick control practices were gathered via a questionnaire in Northwest Pichincha and Quijos River Valley over two years. Resistance rates in the first year (2020-2021) were 67.21% for amitraz, 57.38% for ivermectin, and 67.21% for alpha-cypermethrin. One year later (2021-2022), resistance levels were 59.57% for amitraz, 57.45% for ivermectin, and 68.09% for alpha-cypermethrin, with multi-resistance rates at 67.21% and 65.96% respectively. No significant differences were found between years or locations. Analysis of larval survival data determined lethal doses for tested acaricides. The study emphasizes the association between the lack of acaricide rotation, the incorrect dosage, and the absence of non-chemical measures in tick management could be associated with the development of resistances in ticks. Likewise, this study promotes the need for collaborative efforts to improve control practices and maintain acaricide efficacy.

Records of the Invasive Cattle Tick Rhipicephalus microplus on Wild Hosts and of a Neotropical Tick, Amblyomma dubitatum, on Invasive Alien Mammals, Southern Brazil.

Invasive species threaten wildlife. We detected invasive ticks on wildlife and indigenous ticks on invasive mammals in southern Brazil. The invasive cattle tick Rhipicephalus microplus was found on 12 native mammals and one invasive exotic (Axis axis). The Neotropical tick Amblyomma dubitatum was found on three invasive alien mammal species.

Brazil's battle against Rhipicephalus (Boophilus) microplus ticks: current strategies and future directions.

Ticks are parasitic arthropods that cause significant economic losses to livestock production worldwide. Although Rhipicephalus (Boophilus) microplus, the cattle tick, occurs throughout the Brazilian territory, there is no official program to control this tick, which is the vector of tick fever pathogens. We address the situation of R. (B.) microplus resistance to synthetic acaricides in Brazil, including cattle tick management; the status of tick resistance per Brazilian state; the history of resistance occurrence of different acaricides; multiple resistance occurrence; and the main strategies for integrated tick management. Tick control in Brazil is characterized by management errors. Local laboratories affiliated with federal and state research institutions and universities employ the Adult Immersion Test as a primary diagnostic method to assess acaricide resistance to topically applied drugs. Only three states (Acre, Amapá, and Amazonas) have no reports on resistant populations. Misinformation on tick control strategies, misuse of available products for tick control, no adoption of Integrated Parasite Management (IPM) practices, low technical support to producers, and the high-speed emergence of acaricide-resistant tick populations are the main problems. We also propose a list of needs and priorities for cattle tick control regarding communication, research, and policies.

Strategic control of the cattle tick Rhipicephlaus microplus applied to rotational and silvopastoral grazing systems in subtropical areas.

This work evaluated if strategic control based on no more than three or four annual treatments is useful to control Rhipicephalus microplus infestations on cattle when it is applied to intensive rotational grazing and silvopastoral systems with high stocking rates in subtropical areas. In the intensive rotational grazing system, three annual treatments with chemical acaricides were applied on cattle in two different schemes: between spring and early summer and from late winter and late spring. Strategic control based on three treatments with chemical acaricides from late winter to late spring plus an additional fourth treatment in summer was tested in the silvopastoral system. In the intensive rotational grazing systems, the control schemes allow to reach a significant reduction in the tick load on cattle considering a time interval from spring to autumn. However, the efficacy levels were not high enough in some specific moments, namely, the tick counts of summer and autumn (there were not significant differences between treated and control groups). The scheme evaluated in the silvopastoral grazing system yielded better results than those tested for the intensive rotational system, because significant differences in tick load between treated and control groups were observed in all post-treatment counts and when the analysis was performed for the whole study period. However, values of efficacy in the count-by-count comparison were disparate, ranging from 64.1 to 99.7. Although the efficacy values obtained in the silvopastoral system were better than those of the rotational grazing systems, the total tick load on treated cattle in autumn was not low enough (mean abundance values 25.14 and 38.14). Ticks were more evenly distributed among hosts in late summer and autumn than in spring or early summer, where few hosts carry most of the ticks. Some management strategies as intensive rotational systems or silvopastoral structures can lead to a more efficient forage use, but they imply greater tick challenge than in extensive grazing systems. In these situations, the schemes of strategic control bases on three or four annual treatments should be complemented with additional tactical treatments in late summer or autumn.

A Novel Receptor Binding Progesterone, a Possible Transregulation Mechanism in the Rhipicephalus microplus-Host Interaction.

BACKGROUND: Hormone receptors exert their function through binding with their ligands, which results in cellular signaling activation mediated by genomic or non-genomic mechanisms. The intrinsic molecular communication of tick Rhipicephalus microplus and its host Bos taurus comprises an endocrine regulation involving hormones. In the present study, we performed a molecular and in silico analysis of a Membrane Associated Progesterone Receptor in R. microplus (RmMAPRC). METHODS: The RmMAPRC protein sequence was analyzed with bioinformatics tools, and its structure was characterized by three-dimensional (3D) modeling and molecular docking. A semi-quantitative reverse transcription and polymerase chain reaction (sqRT-PCR) assessed the RmMAPRC gene presence and relative expression in tick organs and embryonic cells. RESULTS: RmMAPRC relative expression in salivary glands, ovaries, and embryonic cells showed overexpression of 3%, 13%, and 24%, respectively. Bioinformatic analysis revealed that RmMAPRC corresponded to a Progesterone Receptor Membrane Component 1 (RmPGRMC1) of ~23.7 kDa, with an N-terminal transmembrane domain and a C-terminal Cytochrome b5-like heme/steroid binding domain. The docking results suggest that RmPGRMC1 could bind to progesterone (P4), some progestins, and P4 antagonists. The phylogenetic reconstruction showed that Rhipicephalus spp. MAPRC receptors were clustered in a clade that includes R. appendiculatus, R. sanguineus, and R. microplus (RmMAPRC), and mammals and helminths MAPRC receptors clustered in two separated clades away from ticks. CONCLUSIONS: The presence of RmPGRMC1 highlights the importance of transregulation as a conserved adaptive mechanism that has succeeded for arthropod parasites, making it a target for tick control.

Hard ticks (Ixodida: Ixodidae) in the Colombian Caribbean harbor the Jingmen tick virus: an emerging arbovirus of public health concern.

BACKGROUND: Ticks are obligate hematophagous ectoparasites involved in transmitting viruses of public health importance. The objective of this work was to identify the Jingmen tick virus in hard ticks from the Colombian Caribbean, an arbovirus of importance for public health. METHODS: Ticks were collected in rural areas of Córdoba and Cesar, Colombia. Taxonomic identification of ticks was carried out, and pools of 13 individuals were formed. RNA extraction was performed. Library preparation was performed with the MGIEasy kit, and next-generation sequencing (NGS) with MGI equipment. Bioinformatic analyses and taxonomic assignments were performed using the Galaxy platform, and phylogenetic analyses were done using IQ-TREE2. RESULTS: A total of 766 ticks were collected, of which 87.33% (669/766) were Rhipicephalus microplus, 5.4% (42/766) Dermacentor nitens, 4.2% (32/766) Rhipicephalus linnaei, and 3.0% (23/766) Amblyomma dissimile. Complete and partial segments 1, 2, 3, and 4 of Jingmen tick virus (JMTV) were detected in the metatranscriptome of the species R. microplus, D. nitens, and A. dissimile. The JMTVs detected are phylogenetically related to JMTVs detected in Aedes albopictus in France, JMTVs detected in R. microplus in Trinidad and Tobago, JMTVs in R. microplus and A. variegatum in the French Antilles, and JMTVs detected in R. microplus in Colombia. Interestingly, our sequences clustered closely with JMTV detected in humans from Kosovo. CONCLUSIONS: JMTV was detected in R. microplus, D. nitens, and A. dissimile. JMTV could pose a risk to humans. Therefore, it is vital to establish epidemiological surveillance measures to better understand the possible role of JMTV in tropical diseases.

Profile of cattle breed sensitivity to the tick Rhipicephalus microplus.

Among cattle, Bos taurus breeds and their crosses are more sensitive to tick infestations than Bos indicus breeds that are more resistant to infestation and more adaptable to tropical climates. The presence of susceptible individuals in herds and inadequate tick control lead to direct and indirect losses in the meat production chain, in addition to increased mortality due to cattle tick fever. The objective of this study was to describe, compare and rank the sensitivity of different breeds of stabled cattle to the tick Rhipicephalus microplus and to present, as an innovative result, a scale called the Tick Ruler. Secondary data on the number of retrieved engorged females, engorged female ticks' weight, egg mass weight and number of larvae were extracted from research reports of experiments conducted over 18 years with eight breeds to describe and report the sensitivity of the breeds to artificial infestation by R. microplus larvae. For analyses, the recovery rate of engorged female ticks and the percentile of dispersion of individuals in their respective races were calculated, and comparison of these percentiles between races was performed. The ranking of the percentiles resulted in the organization of the breeds by their susceptibility to R. microplus; we call this scale the "Tick Ruler." The ruler is a simple, easy-to-understand tool that can be used by technicians and producers to evaluate the tick sensitivity of a breed of interest and can assist producers in decision-making to find a balance between increased production gains and the risk of economic losses depending on the breed composition in a cattle herd.

In silico and In vitro Assessment of Dimeric Flavonoids (Brachydins) on Rhipicephalus microplus Glutathione S-transferase.

INTRODUCTION: Rhipicephalus microplus, an important cattle ectoparasite, is responsible for a substantial negative impact on the economy due to productivity loss. The emergence of resistance to widely used commercial acaricides has sparked efforts to explore alternative products for tick control. METHODS: To address this challenge, innovative solutions targeting essential tick enzymes, like glutathione S-transferase (GST), have gained attention. Dimeric flavonoids, particularly brachydins (BRAs), have demonstrated various biological activities, including antiparasitic effects. The objectives of this study were to isolate four dimeric flavonoids from Fridericia platyphylla roots and to evaluate their potential as inhibitors of R. microplus GST. RESULTS: In vitro assays confirmed the inhibition of R. microplus GST by BRA-G, BRA-I, BRA-J, and BRA-K with IC50 values of 0.075, 0.079, 0.075, and 0.058 mg/mL, respectively, with minimal hemolytic effects. Molecular docking of BRA-G, BRA-I, BRA-J, and BRA-K in a threedimensional model of R. microplus GST revealed predicted interactions with MolDock Scores of - 142.537, -126.831, -108.571, and -123.041, respectively. Both in silico and in vitro analyses show that brachydins are potential inhibitors of R. microplus GST. CONCLUSION: The findings of this study deepen our understanding of GST inhibition in ticks, affirming its viability as a drug target. This knowledge contributes to the advancement of treatment modalities and strategies for improved tick control.

Evaluation of different supportive treatments during packed cell volume replacement in calves naturally infected with tick fever agents.

This study evaluated the effect of different supportive treatments on PCV replacement of dairy calves naturally infected with tick fever (TF) agents, and treated with diminazene and enrofloxacin. Five products were tested as supportive treatments in four experiments. In these experiments, we used Girolando female calves (Gyr × Holstein, genetic ratio of 15/16 and 31/32 Holstein) four to six months old, raised in pasture, naturally infected with TF agents, and infested with R. microplus. Supportive treatment was administered once on day 0 of the study concurrently with specific treatment targeting TF agents. The animals were observed on days 0, 3, and 7. Oral or intravenous administration of a vitamin complex and mineral salts enhanced the increase in PCV and biochemical analytes present in the serum of calves naturally infected with TF agents. No positive effect on PCV values was observed with the administration of (1) invigorating tonic: calcium, casein-peptides and vitamin B12, (2) iron-based stimulant tonic and (3) metabolic tonic: vitamin A, vitamin D, and a fraction of polyunsaturated fatty acids. Supplementation by injection with Type III iron resulted in increased hemoglobin and PCV in treated animals. However, these results did not occur with iron citrate. Therefore, more studies with Type III iron need to be performed. Supportive treatment conferred no advantage in animals with no history of reduced PCV.

In vitro and in silico studies of the acaricidal and anticholinesterase activities of Randia aculeata seeds against the southern cattle tick Rhipicephalus (Boophilus) microplus.

Rhipicephalus (Boophilus) microplus is a leading cause of significant economic losses in the livestock industry, and tick populations have developed multiple forms of resistance to acaricides; therefore, the potential of novel natural bioactive compounds that are effective for targeting ticks must be addressed. The aim of this study was to evaluate the acaricidal and anticholinesterase activities of R. aculeata seeds and to identify naturally occurring compounds that potentially inhibit anticholinesterase through in silico docking. The acaricidal activity of the extract of R. aculeata seeds against larval and adult R. microplus ticks was assessed through immersion tests. Inhibition of anticholinesterase activity was measured spectrophotometrically. Extracts of R. aculeata seeds showed activity against larvae and engorged females of R. microplus, and a reduction in the reproductive index were also observed. Rutin, chlorogenic acid, quercetin, and epicatechin exhibited noteworthy interactions with the active site residues of RmAChE. These findings could significantly contribute to the exploration of novel natural products that can potentially inhibit RmAChE and could be used in the development of new acaricides for tick control.

Comparative analysis of Rhipicephalus microplus (Canestrini, 1888) infestation in pure breed (Hereford) and cross breed (Braford) cattle herds subjected to the same chemical treatments.

The aim of this work was to analyze the R. microplus (Canestrini, 1888) infestation in two bovine herds with different degrees of natural resistance (i.e., Hereford and Braford) to ticks subjected to an identical chemical treatment scheme to ticks at the same farm, to demonstrate the impact on tick control of the incorporation of a more resistant bovine breed. Two groups of ten Hereford and Braford cows each were subjected to eleven chemical treatments between August 2022 and October 2023 (four fluazuron, two fipronil 1%, one ivermectin 3.15% and four immersion in a dipping vat with a combination of cypermethrin 10% and ethion 40%). Tick population was shown to be susceptible to ivermectin, fluazuron and the mix cypermethrin 10%-ethion 40% and resistant to fipronil according to in vitro tests. Tick infestation was significantly greater in the Hereford cows than in the Braford cows. Tick infestation in both Hereford and Braford breeds was similar when treatment with functional drugs was applied, but when a block of the treatments was done with drugs with decreased functionality due to resistance (i.e. fipronil), treatment failure was manifested more strongly in the most susceptible breed. The incorporation of cattle breeds with moderate or high resistance to R. microplus is instrumental to optimize the efficacy and sustainability of chemical control of ticks in a scenario where resistance to one or more chemical groups is almost ubiquitous, because it favors the biological control of this parasite.

Ticks (Acari: Ixodidae) and rickettsiae associated with wild boars in a rural area of Minas Gerais, Brazil.

Wild boars or feral pigs are classified by the Brazilian Institute for the Environment and Renewable Resources (IBAMA) in "Category I of invasive exotic species". They cause economic losses, harm the environment, serve as hosts and reservoirs for several zoonotic disease agents, and provide a blood meal for tick species that act as vectors for zoonotic diseases. The objective of this study was to identify tick species on wild boars, assess host-seeking ticks in the related environment, and identify other potential tick hosts coexisting with wild boars on a farm located in the state of Minas Gerais, southeastern Brazil. Additionally, the study aimed to determine the presence of rickettsiae in these arthropods and assess the exposure of wild boars to rickettsiae species from the Spotted Fever Group and Rickettsia bellii through serology. A total of 3585 host-seeking ticks from three species (Amblyomma sculptum - 41.58%; Amblyomma dubitatum - 0.39% and Rhipicephalus microplus - 0.05%) were collected in the environment and A. sculptum was the most abundant species. Thirty-one wild boars were evaluated, resulting in the collection of 415 ticks, all of which were A. sculptum. Rickettsia DNA was not detected in samples of A. sculptum and R. microplus from the environment or in A. sculptum ticks from wild boars. However, all A. dubitatum ticks (n = 14) had Rickettsia bellii DNA confirmed by the species-specific PCR protocol. Out of the 31 serum samples from wild boars, 24 reacted with at least one Rickettsia antigen. Among these, seven individuals exhibited a reaction to a probable homologous antigen (PHA) of three rickettsiae species: R. rickettsii (n = 3), R. amblyommatis (n = 3) and R. rhipicephali (n = 1). Despite the high prevalence of seroreactivity, titers were low, indicating limited exposure to Rickettsia spp. Camera traps generated 874 animal records, capturing a total of 1688 individuals. At least 11 species of birds and 14 species of mammals (12 wild and two domestic) shared the environment with wild boars and potentially shared ticks with them. These findings provide baseline information for understanding the sharing of ticks and tick-borne pathogens between wild boars and other animals within the Cerrado biome. Further studies are necessary to monitor the potential and actual risk of wild boars to harbor infected ticks and their role in the transmission and maintenance cycle of Rickettsia spp.

Chemical Composition and Acaricidal Activity of Essential Oil of Lavandula dentata L. on Engorged Females of Rhipicephalus (Boophilus) microplus (Acari: Ixodidae).

PURPOSE: Rhipicephalus (Boophilus) microplus is one the most significant ectoparasite in cattle farming in tropical and subtropical regions, causing problems to livestock health worldwide. The control of this ectoparasite primarily relies on the use of synthetic acaricides. However, the emergence of acaricide resistance has stimulated the search for new control alternatives, including phytocompounds with acaricidal and insecticidal potential. The aim of this study was to evaluate the acaricidal potential of Lavandula dentata essential oil against the engorged females of R. (B.) microplus. METHODS: Engorged females were obtained from infested bovines in dairy farms in Pernambuco, Brazil. L. dentata essential oil was extracted, and adult immersion test assays were performed using the following oil concentrations: 0.2%, 0.4%, 0.6%, 0.8%, and 1%. RESULTS: L. dentata essential oil at a concentration of 1% was lethal to all engorged females, and concentrations of 0.6% and 0.8% caused mortality of 98.6% and 99.1%, respectively. These concentrations disrupted the reproductive capacity of engorged females, reducing oviposition by more than 90% and preventing egg hatching by over 87%. CONCLUSION: The data revealed that L. dentata essential oil possesses effective pharmacological properties against R. (B.) microplus and could be used for tick control following in vivo evaluation, thus contributing to mitigating the negative impacts of synthetic acaricide use.

METARHIZIUM ANISOPLIAE SENSU LATO NATIVE TO LIVESTOCK SOILS CAUSES HIGH MORTALITY ON RHIPICEPHALUS MICROPLUS LARVAE, ADULTS AND AFFECTS THEIR REPRODUCTION.

The acaricidal effect of 14 strains of Metarhizium anisopliae sensu lato isolated from soil of livestock farms in the Mexican tropics was evaluated against larvae and engorged females, and during the laying and hatching of eggs of Rhipicephalus microplus (Ixodida: Ixodidae). For each fungal strain, the larvae mortality percentage was evaluated through a larval immersion test, while the reproductive efficiency indices in engorged females were measured using adult immersion tests at a dose of 1 × 108 conidia/ml. All strains of M. anisopliae (s.l.) proved to be highly effective against R. microplus larvae (66-100%) and engorged females (100%). The strains also showed a good effect in inhibiting egg laying (16.45-56.38%) and a moderate effect in decreasing egg hatching (5.24-32.68%). Two strains demonstrated to be effective against all development phases of R. microplus in an integrated manner.

Diversity of midgut microbiota in ticks collected from white-tailed deer (Odocoileus virginianus) from northern Mexico.

Ticks host different pathogens as endosymbiont and nonpathogenic microorganisms and play an important role in reproductive fitness and nutrient provision. However, the bacterial microbiomes of white-tailed deer ticks have received minimal attention. This study aimed to examine the bacterial microbiome of ticks collected from Odocoileus virginianus on the Mexico-United States border to assess differences in microbiome diversity in ticks of different species, sexes, and localities. Five different tick species were collected: Rhipicephalus microplus, Dermacentor nitens, Otobius megnini, Amblyomma cajennense, and A. maculatum. The tick microbiomes were analyzed using next-generation sequencing. Among all tick species, the most predominant phylum was Proteobacteria, followed by Actinobacteria and Firmicutes. The ticks from Tamaulipas and Nuevo León presented the highest bacterial species diversity. Acinetobacter johnsonii and A. lwoffii were the common bacterial species in the microbiome of all ticks, Coxiella were present in R. microplus, and Dermacentor nitens also exhibited a Francisella-like endosymbiont. The microbiome of most females in D. nitens was less diverse than that of males, whereas R. microplus occurs in females, suggesting that microbiome diversity is influenced by sex. In the bacterial communities of A. maculatum and O. megnini, Candidatus Midichloria massiliensis, and Candidatus Endoecteinascidia fumentensis were the most predominant endosymbionts. These results constitute the initial report on these bacteria, and this is also the first study to characterize the microbiome of O. megnini.

Efficiency of fluralaner pour-on in different strategic control protocols against Rhipicephalus microplus on Brangus cattle in a tropical area.

BACKGROUND: The occurrence of higher winter temperatures in Brazilian areas with tropical and highland climates may result in a fifth peak of tick populations during winter in addition to the four generations previously described. Therefore, a strategic control protocol was developed with treatments in two seasons with the objective of controlling the generations of ticks that occur in spring/summer and those that occur in autumn/winter. METHODS: The study was conducted in Mato Grosso do Sul, Brazil, from the beginning of the rainy season, November 2020, to October 2021. In a randomized block design, 36 calves were distributed into three groups: (i) negative control; (ii) traditional strategic control in one season (SC1S), at the beginning of the rainy season; and (iii) strategic control in two seasons (SC2S), at the beginning and end of the rainy season. The SC1S strategic control group was treated on day 0, November 2020, and twice more with intervals of 42 days. The SC2S group received three more treatments beginning on day 182, May 2021, with intervals of 42 days. All treatments consisted of 5% fluralaner (Exzolt® 5%) delivered via a pour-on dose of 1 mL/20 kg body weight. Counts of semi-engorged female ticks were performed on day 3 and every 14 days thereafter, and the animals were weighed at the same time. RESULTS: Fluralaner showed a mean efficacy of more than 95% up to day 294. The two treated groups showed a decrease (P < 0.05) in the average number of ticks on day 3. In the SC2S group, the means were close or equal to zero throughout the study, while in the SC1S group, the means did not differ (P > 0.05) from those of the control group from day 231 onward. The final mean weight gain of each group was 76.40 kg, 98.63 kg, and 115.38 kg for the control, SC1S, and SC2S groups, respectively, differing (P < 0.05) from each other. CONCLUSIONS: Therefore, three applications of fluralaner, with one application every 42 days from the beginning of the rainy season in the middle spring, resulted in effective tick control for 224 days. When three additional treatments were given in autumn/winter with intervals of 42 days between applications, tick counts were reduced throughout the year. This strategic control approach may be indicated in years with climatic conditions that allow that population peaks are expected to occur in the autumn/winter period.

Enzootic stability of tick fever in Holstein calves grazing in a tropical region, subjected to strategic cattle tick control with fluralaner.

BACKGROUND: In 2022, fluralaner was launched on the market for use in the control of the cattle tick Rhipicephalus microplus after showing 100% efficacy in registration trials against the causative agents of cattle tick fever (TFAs). The aim of the present study was to determine whether a strategic control regimen against R. microplus using fluralaner (FLU) in Holstein calves grazing in a tropical region would alter the enzootic stability status of cattle tick fever, triggering outbreaks in these animals up to 22 months age. METHODS: In this study, a group of calves treated with FLU was compared with a control group treated with the regimen currently being used on the farm, which consisted of the fipronil + fluazuron formulation (FIFLUA). In the first experiment, the efficacy of the FIFLUA pour-on formulation was evaluated in a field study. In the second experiment, which lasted 550 days, two experimental groups (n = 30/group) of Holstein calves naturally infested with R. microplus were analyzed. Calves aged 4 to 10 months received either a specific treatment regimen with FLU (experimental group) or FIFLUA (control group). During this period, tick counts, animal weight measurement, feces collection (to determine eggs and oocysts per gram of feces), tick fever monitoring, blood smears (to ascertain enzootic stability of the herd), PCR testing for TFAs and serology (indirect enzyme-linked immunosorbent assay [iELISA]) were performed. All calves were evaluated for signs of tick fever between ages 11 and 22 months. RESULTS: FIFLUA showed an acaricidal efficacy of > 90% from post-treatment days 14 to 35. Regarding treatments against the TFAs, the average number of treatments was similar between groups, but animals treated with FLU had a smaller reduction in packed cell volume on some of the evaluation dates of the second and third treatment against TFAs. In calves aged 10 months in the FLU group, B. bovis was not detected by PCR (0/15 samples), 40% of the samples had antibody titers and 33% (10/30) of the samples had positive blood smears. Regarding B. bigemina, > 86% of the samples in both groups tested positive for B. bigemina DNA and antibodies; there was no difference in the antibody titers between the groups. There were no clinical cases of cattle tick fever in calves aged 11 to 22 months. CONCLUSIONS: In comparison with the control treatment, the strategic control regimen against R. microplus with FLU that was implemented in the present study did not negatively affect the enzootic stability status of A. marginale and B. bigemina in the herd up to 22 months of age. The enzootic stability status of B. bovis was not reached by either group. These results likely represent a characteristic of the local tick population, so further studies should be performed.

Biology of the non-parasitic phase of the cattle tick Rhipicephalus (Boophilus) microplus in an area of Amazon influence.

BACKGROUND: Rhipicephalus (Boophilus) microplus is the most important tick species affecting cattle in the world. Under field conditions, the non-parasitic phase of R. (B.) microplus is unknown in the Amazon biome, including Brazil. The present study aimed to evaluate the non-parasitic phase of R. (B.) microplus in field (grass plots) and laboratory conditions. METHODS: The study was conducted from September 2020 to April 2022 in an Amazonian region (Maranhão State, Brazil). We evaluated the biological parameters of R. (B.) microplus under laboratory and field conditions. Engorged females were exposed to experimental conditions every 14 days, totaling 20 months of study. The following biological parameters were observed: pre-oviposition period, egg mass incubation period, and maximum larval survival period. RESULTS: Abiotic data (e.g., temperature and humidity) varied little throughout the year. Precipitation was the factor that varied the most throughout the year (dry ~ 30 mm3 and rain 400 mm3), and the parameters of pre-oviposition and pre-hatching are longer during the rainy season. A possible negative effect of the dry season on the percentage of hatched eggs was observed. Larval longevity in the plots of both control and free females was short (mean ~ 50-60 days), below that recorded for larvae under controlled conditions (mean ~ 95 days). CONCLUSIONS: Rhipicephalus (Boophilus) microplus was able to complete its non-parasitic phase by producing host-seeking larvae in the pasture during all months of the study. The results indicate that R. (B.) microplus can complete up to six generations per year in biome Amazon. To our knowledge, this is the highest number of annual generations for R. (B.) microplus in Latin America.

Alpha- and beta-pinene isomers act differently to control Rhipicephalus microplus (Acari: Ixodidae).

The cattle tick Rhipicephalus microplus is an ectoparasite of high importance in veterinary medicine and public health. Since synthetic chemicals used to control these ticks can select resistant strains and cause toxic effects in their hosts, there is a need to identify effective substances with fewer adverse effects. For this reason, we investigated the effects of alpha- and beta-pinene, known for their various biological effects, on the mortality and reproductive performance of R. microplus engorged female ticks. The products were diluted in a 2% Tween 80 aqueous solution. The ticks were first weighed and then immersed in the test solutions for five minutes. Then, they were dried with paper towels and fixed dorsoventrally in Petri dishes, totalling five treatment groups for each pinene and a control group treated with the solvent alone. The ticks were monitored daily for mortality, and their eggs were collected and weighed. The larval hatching rate was estimated, and the pre-oviposition and incubation periods were determined. From these data, the following parameters were calculated: egg production index, fertility rate, estimated reproduction rate, percentages of reduction in oviposition and hatching, and product efficacy. Alpha-pinene showed better results at higher concentrations, unlike beta-pinene, which was more effective at lower concentrations. The effectiveness of alpha-pinene was 74% at a concentration of 14.0 µL/mL, while beta-pinene showed 78% efficacy at 2.0 µL/mL. The results indicated for the first time different effects of two isomers in ticks, suggesting that these compounds act on R. microplus females in different ways.