Control of Rhipicephalus microplus on taurine cattle with fluralaner in a subtropical region.

BACKGROUND: In Rio Grande do Sul, Brazil, a region with a subtropical climate, Rhipicephalus microplus is present in taurine cattle raised for beef and milk. In addition, ticks resistant to multiple acaricides are present in this region. Recently, fluralaner (isoxazoline) was launched on the market. Thus, there is a need to evaluate the effects of fluralaner for the control of R. microplus on taurine cattle. In addition, occurrence of myiasis by Cochliomyia hominivorax larvae after tick parasitism and weight gain of cattle during the experimental period were evaluated. METHODS: Thirty naturally infested cattle were divided into two experimental groups: T01, treated with fluralaner (2.5 mg/kg) pour-on; T02, control. T01 received fluralaner on Days 0 (early summer in January), 42 and 84 (early autumn), whereas T02, a control group, received palliative treatment with a spray formulation when the group mean was ≥ 30 ticks. Counts of R. microplus females and calculation of the efficacy of fluralaner were performed on Days 3, 7, 14, 28, 35, 42, 56, 70, 84, 98, 112 and 126. The occurrence of myiasis was assessed throughout the study period. In addition, the weight, weight gain and daily weight gain of the animals were evaluated. RESULTS: In the 12 evaluations performed, the parasitic load of T01 was near zero. Fluralaner showed 99.5% efficacy on the 3rd day after the first treatment and 100% efficacy from Day 7 to Day 126. Cochliomyia hominivorax larvae (n = 6; p = 0.0251) were found only in the control group (T02). At the end of the study, the animals subjected to treatments with fluralaner gained 32.8 kg more than the animals in the control group. CONCLUSIONS: Application of fluralaner in summer and autumn, with 42-day intervals between treatments, was effective to control R. microplus on taurine cattle, which also gained more weight than control cattle. Additionally, no cases of myasis were documented in animals treated with fluralaner.

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.

Toltrazuril + fenbendazole for cattle: Pharmacokinetics and efficacy against Eimeria spp. and gastrointestinal nematodes.

The present work evaluated the pharmacokinetics and efficacy of the association of 15cmg/kg toltrazuril +5cmg/kg fenbendazole against Eimeria spp. and gastrointestinal nematodes (GINs) in calves of different regions of Brazil (Center-West, Southeast, and South). A total of seven experiments were carried out, five of which determined formulation efficacy against Eimeria spp., considering the following aspects: therapeutic, preventive, metaphylactic, and residual efficacy. Therapeutic efficacy experiments for GINs were carried out by parasitological necropsy. The toltrazuril + fenbendazole association demonstrated ≥95% efficacy against Eimeria spp. for 21 days post-treatment (DPT). When used preventively and metaphylatically, the same association demonstrated ≥97% efficacy against E. zuernii, E. ellipsoidalis, E. cylindrica, E. bovis, E. wyomingensis and E. auburnensis. Toltrazuril + fenbendazole administered seven days before challenge was 100% effective against all these Eimeria species. Results of therapeutic, preventive, metaphylactic and residual efficacies can be related to the pharmacokinetic results, especially considering toltrazuril sulfone, which was detected in animal plasma for a longer period than the parent compound. Toltrazuril + fenbendazole achieved 100% anthelminthic efficacy against the GINs Haemonchus placei (L4), Cooperia pectinata and Oesophagostomum radiatum; 99.94% against adult H. placei; and 99.98% against C. puntacta. The association of toltrazuril + fenbendazole, associated with other measures, is an important and suitable tool for the control and treatment of Eimeria spp. and GINs in young cattle.

Two protocols using fluralaner for Rhipicephalus microplus strategic control on taurine cattle in a tropical region.

BACKGROUND: The present study aimed to evaluate the effects of different treatment strategies using a new commercial formulation containing pour-on fluralaner on Rhipicephalus microplus infestation in cattle and in pastures in a tropical climate region where up to five generations of this tick species can occur per year. METHODS: Forty-five naturally infested cattle were divided into three experimental groups: T01, treated with fluralaner (2.5 mg/kg) pour-on every 42 days; T02, the cattle received the first treatment with fluralaner on Day 0 but the next treatment involved a weekly visual evaluation; T03, control, received palliative treatment with a spray formulation when the group mean was ≥ 30 ticks. Counts of female R. microplus were performed weekly until day 343, and larval counts on pasture were performed on Days 0, 30, and 60 and every 30 days until Day 330. RESULTS: Using fluralaner, six applications were performed in Group T01, and four were performed in Group T02. In the control group (T03), it was necessary to perform eight palliative acaricide treatments with the spray formulation. The animals in T01 and T02 showed lower mean tick counts (p ≤ 0.05) than the control group (T03) on 28 and 27 of the 49 evaluated dates, respectively. In the paddock where the animals were kept as controls, the R. microplus larvae counts increased to 1458. In the paddocks where the animals were treated with fluralaner, the number was ≤ 19 per paddock during the study. CONCLUSIONS: The different strategic treatment protocols performed with pour-on fluralaner (2.5 mg/kg) over a year in taurine cattle in a tropical region with a history of up to five annual generations of cattle ticks were effective, maintaining levels of R. microplus infestations in animals and in pastures close to zero in most of the study. Depending on the retreatment criterion adopted, the number of applications per year may be lower, resulting in a reduction in the mean cost of acaricide treatment per year and lower exposure of R. microplus populations to the active ingredient, resulting in lower resistance and selection pressure.

Essential oils and isolated compounds for tick control: advances beyond the laboratory.

BACKGROUND: Tick control is a worldwide challenge due to its resistance to acaricides. Essential oils (EOs) and isolated compounds (EOCs) are potential alternatives for tick control technologies. METHODS: A review with EOs and EOCs, under field and semi-field conditions, was performed based on Scopus, Web of Science and PubMed databases. Thirty-one studies published between 1991 and 2022 were selected. The search was performed using the following keywords: "essential oil" combined with "tick," "Ixodes," "Argas," "Rhipicephalus," "Amblyomma," "Hyalomma," "Dermacentor," "Haemaphysalis" and "Ornithodoros." The words "essential oil" and "tick" were searched in the singular and plural. RESULTS: The number of studies increased over the years. Brazil stands out with the largest number (51.6%) of publications. The most studied tick species were Rhipicephalus microplus (48.4%), Ixodes scapularis (19.4%), Amblyomma americanum and R. sanguineus sensu lato (9.7% each). Cattle (70%) and dogs (13%) were the main target animal species. Regarding the application of EOs/EOCs formulations, 74% of the studies were conducted with topical application (spray, pour-on, foam, drop) and 26% with environmental treatment (spray). Efficacy results are difficult to evaluate because of the lack of information on the methodology and standardization. The nanotechnology and combination with synthetic acaricides were reported as an alternative to enhance the efficacy of EOs/EOCs. No adverse reactions were observed in 86.6% of the studies evaluating EOs/EOCs clinical safety. Studies regarding toxicity in non-target species and residues are scarce. CONCLUSIONS: This article provides a comprehensive review on the use of EOs and EOCs to reduce tick infestations, in both the hosts and the environment. As future directions, we recommend the chemical characterization of EOs, methodology standardization, combination of EOs/EOCs with potential synergists, nanotechnology for new formulations and safety studies for target and non-target organisms, also considering the environmental friendliness.

First report of the efficacy of a fluralaner-based pour-on product (Exzolt® 5%) against ectoparasites infesting cattle in Brazil.

BACKGROUND: This study describes the effectiveness of a novel active pharmaceutical ingredient, fluralaner (isoxazoline class), against important ectoparasites infesting cattle in Brazil. METHODS: A total of 13 studies involving a 5% fluralaner-based pour-on formulation (Exzolt 5%; further referred to as Exzolt) were conducted. Specifically, the effectiveness of this formulation was studied against Rhipicephalus microplus (6 studies), Cochliomyia hominivorax larvae (4 studies), Dermatobia hominis larvae (1 study) and Haematobia irritans flies (2 studies). RESULTS: The therapeutic efficacy of Exzolt was found to exceed 98% at 4 days post treatment (DPT), while persistent efficacy (> 90% efficacy) against repeated infestations of R. microplus was observed for up to 79 DPT. In field studies, ≥ 98% therapeutic efficacy was demonstrated at all study sites by 7 DPT, and a persistent efficacy (> 90% efficacy) was observed for 42, 49 or 56 DPT. Exzolt prevented C. hominivorax eggs from developing to the larval stage, thus mitigating the development of myiasis in cattle naturally and artificially infested with this screworm. The efficacy of Exzolt against D. hominis larvae was 98% at 3 DPT, while persistent efficacy (> 90% effectiveness) was found to last for up to 70 DPT. Against H. irritans, Exzolt showed therapeutic efficacy (≥ 90%) within the first day of treatment at both study sites, while persistent efficacy (≥ 90%) was observed for 7 DPT at one site and for 21 DPT at the other site. CONCLUSIONS: Overall, the results from these studies confirm that Exzolt is therapeutically efficacious against the most important ectoparasites infesting cattle in Brazil. The novel active pharmaceutical ingredient, fluralaner, provides a new treatment option for farmers to control cattle ectoparasites, especially where there is resistance to other chemical classes. In addition, an effective control of ectoparasites will improve overall cattle health and well-being as well as production.

Combination of synthetic acaricides with (E)-cinnamaldehyde to control Rhipicephalus microplus.

This work had the objectives to (1) evaluate the susceptibility of various Rhipicephalus microplus populations to commercial acaricides, and (2) select commercial acaricides (50-80% effective) and evaluate the effects of binary combinations of the phenylpropanoid (E)-cinnamaldehyde with selected commercial acaricides to control R. microplus under laboratory and field conditions. Using adult immersion tests with 116 populations and 14 commercial acaricides, products showing 50-80% effectiveness (percent control) with the lowest number of active ingredients were selected. Acaricides containing amitraz or chlorfenvinphos were tested in combination with (E)-cinnamaldehyde on a field population (strain CM). We found that (E)-cinnamaldehyde enhanced the activity of both commercial acaricides against R. microplus larvae; however, the enhancement was more accentuated when using amitraz. Experiments combining (E)-cinnamaldehyde + amitraz on unfed larvae and engorged females from another population (strain Gyn) were performed, verifying (E)-cinnamaldehyde enhanced the activity of amitraz. In the field experiment, the application of (E)-cinnamaldehyde appeared toxic to the tick hosts (cattle). We concluded that (E)-cinnamaldehyde enhanced the activity of amitraz against unfed larvae and engorged females of R. microplus; however, in the field test this phenylpropanoid caused intoxication in the cattle. Studies searching for new combinations of compounds from essential oils with amitraz deserve attention, as well as studies to develop formulations using amitraz + (E)-cinnamaldehyde that will be efficient and will not have toxic effects in cattle.

Effect of the formulation with fipronil and fluazuron on the reproductive biology and ovaries histopathology of Rhipicephalus microplus engorged females.

This study aimed to evaluate the effects of a commercial formulation containing fipronil and fluazuron on the reproductive biology and the morphology of ovaries from Rhipicephalus microplus engorged females. To carry out the study, three calves were artificially infested every 3 days with approximately 5000 larvae. On day 0, the animals were treated with a commercial formulation containing fipronil (1.25 mg/kg) + fluazuron (2.5 mg/kg). Before the application of the acaricide, engorged females of R. microplus were collected to constitute the control group (10 for biology analyses and 20 for histology analyses). After applying the commercial formulation, naturally detached engorged females were recovered on days + 5, + 10, and + 20 (10 engorged females/day) to evaluate their reproductive biology, and on days + 4, + 12, and + 20 (20 engorged females/day) for histological evaluation of the ovaries. Females from the treated groups produced smaller amounts of eggs, exhibiting lower viability when compared to eggs from the control group (p < 0.05). The ovaries of females from all treated groups (+ 4, + 12, and + 20) showed morphological changes, including: cytoplasmic disorganization, cytoplasmic degradation, irregular shape of the oocyte and germinal vesicle, reduction and vacuolization of yolk granules and oocyte disruption. Oocytes were observed in smaller numbers in all stages of development (I, II, III, IV, and V) and greater numbers of indeterminate oocytes were verified in the ovaries of the treated groups when compared to the control group. Therefore, results showed that the commercial formulation containing fipronil and fluazuron affected the reproductive biology, caused morphological changes in the ovaries, and reduced the number of oocytes in R. microplus engorged females.

Avermectin toxicity in bovines less than thirty days old.

The present study was designed to evaluate possible adverse effects of different dosages of avermectins (abamectin and a combination of ivermectin + abamectin) administered subcutaneously in calves less than one month of age. Clinical as well as biochemical parameters of blood and cerebrospinal fluid (CSF) were evaluated for animals subjected to various treatments. Thirty-five calves were divided into seven groups of five animals each: T01 (control), T02 (abamectin 200 µg/kg), T03 (abamectin 400 µg/kg), T04 (abamectin 600 µg/kg), T05 (ivermectin 450 µg/kg + abamectin 250 µg/kg), T06 (ivermectin 900 µg/kg + abamectin 500 µg/kg) and T07 (ivermectin 1350 µg/kg + abamectin 750 µg/kg). Cerebrospinal fluid and blood samples were collected on day zero (treatment day) and on days 1, 7 and 14 following treatment. The biochemical parameters measured in blood samples were total protein and the AST, GGT and alkaline phosphatase enzymes. In CSF samples, color, aspects, pH, density, cellularity, total proteins, glucose and the CK, ALT and LDH enzymes were evaluated. No neurological toxicity or biochemical changes in the CSF or blood that could be correlated to administration of tested products were observed in this study. Though it is well known that abamectin may lead to intoxication in bovines less than four months of age, based on data from the present study, no adverse clinical effects to the CSF or blood were observed in calves <30 days old that had received up to 600 µg/kg abamectin formulations and up to 1350 µg/kg ivermectin +750 µg/kg abamectin associations. It is possible that the level and activity of the multiple drug resistance gene (MDR1 - ABCB1) present in the calves may have influenced the results obtained in this study. Future studies should be carried out.

The effectiveness of a fixed-dose combination pour-on formulation of 1.25% fipronil and 2.5% fluazuron against economically important ectoparasites and associated pharmacokinetics in cattle.

The present work consisted of eight studies to evaluate the ectoparasiticidal spectrum and determine the pharmacokinetic parameters of a pour-on combination of fipronil 1.25mg/kg+fluazuron 2.5mg/kg for cattle against Rhipicephalus microplus, Haematobia irritans and the larvae of Dermatobia hominis and Cochliomyia hominivorax. The analysis fipronil and fluazuron were performed by liquid chromatography using a mass detector for the detection and quantification of analytes (LC-MS/MS). Additionally, in two of these studies, the animals were artificially infested with R. microplus ticks (stall tests), and the efficacy of this formulation was compared with that of two other standalone pour-on formulations of fipronil 1.0mg/kg and fluazuron 2.5mg/kg. In the two stall studies, 28 calves were artificially infested with 5000 R. microplus (different strains), and daily collections of all of the engorged female ticks that detached from each calf were performed until 60 and 100days post-treatment (dpt). For the R. microplus field trials, 20 bovines were selected by counting the semi-engorged females, and the therapeutic and residual efficacy was evaluated by taking tick counts at 3, 7, 14, 21, 28, 35, 42, 49 and 56dpt. Forty bovines that were naturally infested with Dermatobia hominis larvae were selected, and the numbers of larvae were counted by visual and tactile inspection on 3, 7, 14, 28, 35, 42 and 49dpt. To address the efficacy on C. hominivorax larvae, two circular skin incisions (one on each side of the body) measuring approximately 4cm in diameter each were made in 12 crossbred calves, and the natural exposure of the lesions to C. hominivorax infestations was then allowed. The incisions from the 12 animals were carefully examined daily from 1 to 10dpt. Based on the PK results obtained for this pour-on combination containing fipronil 1.25mg/kg+fluazuron 2.5mg/kg, the maximum concentrations (Cmax) and the half-lives (T1/2) of these two active ingredients were detected on days 2, 5/6 and 19 (±2)/24, 4 (±3.5) days for fipronil and fluazuron, respectively. Furthermore, the combination showed higher therapeutic and residual efficacy against R. microplus (P≤0.05) when compared with commercial standalone formulations that were administered separately. A high efficacy for this new combination was also found against C. hominivorax and D. hominis larvae (efficacy≥99%). This study's results show that the combination of these two active ingredients, as opposed to their separate use, could represent a tool for extending the life cycle of these two molecules against cattle ectoparasites, especially R. microplus. Further studies would be desirable to further confirm this.