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

Authors: ARAFA, WALEED - Beni Suef University - Egypt; ABOELHADID, SHAWKY - Beni Suef University - Egypt; MOAWAD, ABEER - Beni Suef University - Egypt; SHOKEIR, KHALID - Animal Health Research Institute; AHMED, OSAMA - Beni Suef University - Egypt; Perez De Leon, Adalberto - Beto

Submitted to: Veterinary Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/4/2021
Publication Date: 1/4/2021
Citation: Arafa, W.M., Aboelhadid, S.M., Moawad, A., Shokeir, K.M., Ahmed, O.M., Perez De Leon, A.A. 2021. Control of Rhipicephalus annulatus resistant to deltamethrin by spraying infested cattle with synergistic eucalyptus essential oil-thymol-deltamethrin combination. Veterinary Parasitology. 290:109346. https://doi.org/10.1016/j.vetpar.2021.109346.
DOI: https://doi.org/10.1016/j.vetpar.2021.109346

Interpretive Summary: The tick scientifically known as Rhipicephalus annulatus is an economically important external parasite and vector of disease agents causing bovine babesiosis and anaplasmosis that impact cattle production in subtropical parts of the world where it is established. Chemicals with the ability to kill ticks, also known as acaricides, are used extensively to control infestations in cattle. However, this approach exerts strong selection for populations of this cattle tick that become resistant to acaricidal products including those that contain members of the pyrethroid class of synthetic acaricides like deltamethrin. Plant products with acaricidal activity including several essential oils and their constituents are alternatives that could be used alone or in combination with pyrethroids to control cattle ticks that are resistant to deltamethrin. In this study we conducted experiments in the laboratory and sprayed cattle with mixtures of eucalyptus essential oil, thymol, which is a constituent of oil of thyme known to have acaricidal properties, and deltamethrin. The combination of eucalyptus oil, thymol, and deltamethrin was the most potent, and when sprayed safely on naturally infested cattle it showed 95% efficacy against R. annulatus resistant to deltamethrin. These findings document that combinations of natural and synthetic products can be part of integrated management solutions to the problem with widespread resistance to pyrethroids like deltamethrin in populations of cattle ticks, including R. annulatus, around the world.

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