Efficacy of Tagetes minuta (Asteraceae) essential oil against Rhipicephalus sanguineus (Acari: Ixodidae) on infested dogs and in vitro

Effect of Tagetes minuta essential oil on the central nervous system of unfed Rhipicephalus sanguineus sensu lato 'tropical lineage' ticks

Rhipicephalus sanguineus sensu lato 'tropical lineage' (Acari: Ixodidae) is considered a sanitary concern due to its role as a disease vector. Tick strains resistant to synthetic acaricides have caused difficulties in their control, besides synthetic acaricides are harmful to the environment and to the health of non-target animals. The research of plants with acaricidal and repellent properties has proved to be an efficient alternative in tick control. The genus Tagetes spp. excels for its use as traditional pest control in households and plantations and also for its potential as an acaricide against R. sanguineus under laboratory conditions. The first aim of the present study was to evaluate the effect of different doses of Tagetes minuta essential oil (TMEO) on the central nervous system (synganglion) in unfed R. sanguineus adults. The histological analysis of synganglion exposed to the different concentrations of TMEO and amitraz 12.5% (50% of the recommended dose in the package insert) showed a significant effect with signs of cell damage including volume increase, loss of shape, and vacuolization, in addition to chromatin alterations such as condensation, margination, and fragmentation. TMEO were analyzed by gas chromatography coupled with mass spectrometry showing the presence of 21 compounds that according to their chemical structure are classified as terpenoids. Among them (Z)-β-ocimene, ocimene, (Z)-tagetone, and verbenone were found in major quantities.

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.

Essential Oils and Melatonin as Functional Ingredients in Dogs

Simple Summary

Phytogenics are plant-based compounds with beneficial actions in feed technology and/or animal health. These so-called plant secondary metabolites are very diverse and with wide possible applications in humans and animals. Among them, essential oils (EOs) are the most used in feed for livestock and pets. Lately, melatonin has acquired new and interesting applications in dogs. Recent studies using EOs and/or melatonin in dog feeding and their involvement in health aspects are presented.

Abstract

The use of nutraceuticals or functional ingredients is increasingly widespread in human food; their use is also widespread in animal feed. These natural compounds generally come from plant materials and comprise a wide range of substances of a very diverse chemical nature. In animals, these compounds, so-called phytogenics, are used to obtain improvements in feed production/stability and also as functional components with repercussions on animal health. Along with polyphenols, isoprenoid compounds represent a family of substances with wide applications in therapy and pet nutrition. Essential oils (EOs) are a group of complex substances with fat-soluble nature that are widely used. Melatonin is an indolic amine present in all living with amphiphilic nature. In this work, we present a review of the most relevant phytogenics (polyphenol, isoprenoid, and alkaloid compounds), their characteristics, and possible uses as nutraceuticals in dogs, with special emphasis on EOs and their regulatory aspects, applied in foods and topically. Additionally, a presentation of the importance of the use of melatonin in dogs is developed, giving physiological and practical aspects about its use in dog feeding and also in topical application, with examples and future projections. This review points to the combination of EOs and melatonin in food supplements and in the topical application as an innovative product and shows excellent perspectives aimed at addressing dysfunctions in pets, such as the treatment of stress and anxiety, sleep disorders, alopecia, and hair growth problems, among others.

Thymol and eugenol microemulsion for Rhiphicephalus sanguineus sensu lato control: Formulation development, field efficacy, and safety on dogs

The present study aimed to develop a microemulsion formulation containing thymol and eugenol for field control of Rhipicephalus sanguineus sensu lato on dogs, as well to evaluate its safety and the physical characteristics of the formulation. The microemulsion using thymol and eugenol (5.0 + 5.0 mg/mL) had as vehicles water, propylene glycol, polysorbate 80 and canola oil. On the next day the preparation (formulation freshly prepared) and after 24 months, the size of the microemulsion droplets, polydispersion index (PdI), organoleptic properties (color, viscosity), and presence of precipitate in the microemulsion were evaluated. For the field assay, on day -1, 10 English Cocker Spaniel dogs were experimentally infested with 200 larvae, 100 nymphs and 30 adults of R. sanguineus s.l. On day 0, after tick counts, the animals were divided into two groups: treated with the freshly prepared microemulsion (10 mL/kg), and control, which received the vehicle (10 mL/kg). Tick counts on dogs were performed daily for three more days. Engorged females were recovered from the dogs and their biological and reproductive parameters were monitored. The dogs' clinical parameters (temperature, mucosa color, and general physical condition) were evaluated daily. In addition, blood samples were collected before infestation to verify hematological (packed cell volume) and biochemical parameters (total serum protein, albumin, globulins, creatinine, urea, alanine transaminase, aspartate aminotransferase, and alkaline phosphatase). Freshly prepared and 24-month aged microemulsions had droplets with mean sizes of 30.94 nm and 27.93 nm, and PdI values of 0.214 and 0.161, respectively. In addition, no difference in the organoleptic properties and no precipitation formation were observed, indicating physical stability. Treatment with the microemulsion resulted in reduction of larvae (p < 0.05) parasitizing the dogs on day 1 while the number of nymphs and adults was not reduced (P> 0.05). In the evaluation of the reproductive biology of engorged females, the larval hatchability (%) was compromised (p < 0.05), and the microemulsion had control rate of 85.5 %. The microemulsion and its vehicles did not change the clinical, hematological and biochemical parameters of the dogs. We concluded that the microemulsion was efficient against R. sanguineus s.l. by reducing the number of larvae and affecting the reproductive parameters of engorged females, safe for dogs, and stable (physical stability) during a two-year interval.

Acaricidal effect of Schinus molle (Anacardiaceae) essential oil on unengorged larvae and engorged adult females of Rhipicephalus sanguineus (Acari: Ixodidae)

The current concern about resistance to acaricides and the impact of toxic waste on the environment has led to the search of vegetal alternatives in the control of the brown tick of the dog Rhipicephalus sanguineus. Schinus molle L. (Anacardiaceae) derivatives have been associated with insecticidal, antimicrobial and antiprotozoal activities and essential oil showed to be lethal to R. microplus larvae. This study aimed at evaluating the acaricidal effect of essential oil of S. molle (EO_Sm) on engorged adult females and larval stages of R. sanguineus. One-hundred engorged females were obtained from the ears, interdigital spaces, neck, groin and base of the tail of two cross-bred dogs. The larvae package test was accomplished with 21-day-old larvae and five concentrations (v/v) of EO_Sm (0.125, 0.25, 0.50, 1 and 2%) in an anionic detergent, a synthetic acaricide (cypermethrin) and detergent and deionized water as controls. The immersion adult test was carried out with nine concentrations (0.125, 0.25, 0.50, 1, 2, 4, 8, 16, 20%) of the EO_Sm. At the concentration of 2%, EO_Sm caused 99.3% of larval mortality. In adults, inhibition of oviposition, egg hatching (EH) and reproductive efficiency (RE) values were dose-dependent from 4 to 20% EO_Sm; the lowest values of EH (29.62) and RE (22.61) were achieved with 20% EO_Sm. Strong and negative correlations were found between concentration of EO_Sm and EH (r = - 0.948) and between concentration of EO_Sm and RE (r = - 0.985). This study demonstrated for the first time the acaricidal effect of EO_Sm on larvae and reproductive parameters of engorged adult females of R. sanguineus.