Abstract
BackgroundTreatment of Psoroptes ovis in cattle is limited to topical acaricides or systemic treatment with macrocyclic lactones. Treatment failure of macrocyclic lactones has been reported. The aim of this study was to evaluate a potential alternative treatment against P. ovis.MethodsThe acaricidal activity against P. ovis of four plant-derived essential oil components, i.e. geraniol, eugenol, 1,8-cineol and carvacrol, was assessed in vitro and in vivo. In vitro contact, fumigation and residual bioassays were performed. In addition, 12 Belgium Blue cattle were artificially infested and treated topically once a week for three successive weeks with carvacrol in Tween-80 (treatment group) or with Tween-80 alone (control). The efficacy of carvacrol was determined by the reduction in lesion size and mite counts. Six additional animals were topically treated with carvacrol to assess local adverse reactions.ResultsThree components showed a concentration-dependent acaricidal activity in a contact assay, with LC50 of 0.56, 0.38 and 0.26% at 24 h for geraniol, eugenol, and carvacrol, respectively. However, 1,8-cineol showed no activity at any of the tested concentrations in a contact bioassay. In a fumigation bioassay, carvacrol killed all mites within 50 min after treatment, whereas geraniol, eugenol and 1,8-cineol needed 90 to 150 min. Following a 72 h incubation period in a residual bioassay, carvacrol killed all mites after 4 h of exposure to LC90, while geraniol and eugenol killed all mites only after 8 h exposure. Based on these results, carvacrol was further assessed in vivo. Mite counts in the treatment group were reduced by 98.5 ± 2.4% at 6 weeks post-treatment, while in the control group the mite population had increased. Topical application of carvacrol only caused mild and transient erythema 20 min after treatment. No other side effects were observed.ConclusionsConsidering the strong acaricidal activity of carvacrol in vitro and in vivo and the mild and transient local side effects, carvacrol shows potential as an acaricidal agent in the treatment of P. ovis in cattle.
Highlights
Treatment of Psoroptes ovis in cattle is limited to topical acaricides or systemic treatment with macrocyclic lactones
Eugenol and carvacrol showed a dosedependent acaricidal activity and a low mortality rate was observed when adult mites were brought into contact for 24 h with a concentration of 0.16%
Geraniol had no activity at concentrations below 0.63% and 1,8-cineol did not show any acaricidal activity at any of the concentrations tested
Summary
Treatment of Psoroptes ovis in cattle is limited to topical acaricides or systemic treatment with macrocyclic lactones. Psoroptes ovis is a common ectoparasitic mite of sheep, cattle and rabbits. It is the causative agent of a ubiquitous skin disease, which is commonly referred to as psoroptic mange. Psoroptic mange can be treated by local administration of amitraz or pyrethroids or systemic administration of macrocyclic lactones. Chemical drugs have been highly effective against psoroptic mange in the past decades [6,7,8,9], their frequent and/or incorrect usage has resulted in a reduced efficacy due to emerging drug resistance, leading to inadequate control [10,11,12]. There is an urgent need to develop new effective and safe acaricidal agents for treatment and control of animal acariasis
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