A Potential Anthelmintic Phytopharmacological Source of Origanum vulgare (L.) Essential Oil against Gastrointestinal Nematodes of Sheep

SIMPLE SUMMARY: Inappropriate use of regular anthelmintic drugs has led to the development of anthelmintic resistance in sheep gastrointestinal nematodes (GINs) and consequently caused huge economic losses. Therefore, researchers worldwide are making efforts in finding novel strategies to control these parasites, which are mostly based on the rational use of synthetic drugs and the use of various alternatives, such as botanical anthelmintics. The aim of this study was to evaluate the anthelmintic efficacy of the essential oil (EO) of oregano (Origanum vulgare (L.)) against sheep GINs and to demonstrate the possibility of its use in veterinary practice. For obtaining clear results, both in vitro (egg hatch test) and in vivo efficacy tests (fecal egg count reduction test), as well as toxicity studies, on the hosts (clinical examination, blood count, and liver or kidney function test) were performed. The egg hatch test demonstrated the anthelmintic potential of the tested EO with an efficacy of 71.3%–93.7%, which was also demonstrated in the fecal egg count reduction test with an efficacy of 60.1% in total (on the second farm, 78.26%) shown on day 14 after treatment. Moreover, no negative or side effects of the applied EO formulation to the sheep were noticed in toxicity studies. The obtained results indicate the high potential of the O. vulgare EO for use in veterinary practice to control sheep GINs, as a part of an integrated strategy aimed to reduce the use of conventional anthelmintics. Therefore, these results may be significant for the future management of these infections. ABSTRACT: The development of anthelmintic resistance in sheep gastrointestinal nematodes (GINs) requires novel strategies for the sustainable control of these parasites. This study aimed to evaluate the anthelmintic efficacy of the Origanum vulgare (L.) essential oil (EO) against sheep GINs and to evaluate the possibility of its use in control practice. The in vitro egg hatch test was conducted at eight different concentrations (50, 12.5, 3.125, 0.781, 0.195, 0.049, 0.025, and 0.0125 mg/mL) of the tested EO. For the in vivo fecal egg count reduction test, the EO of O. vulgare was administrated orally at a mean single dose of 150 mg/kg to sheep from two farms in Southern Italy, whereby potential toxic effects to the hosts were also evaluated. In the egg hatch test, the inhibition of egg hatchability varied from 71.3% to 93.7%, depending on the concentration used. The high anthelmintic potential was confirmed in the fecal egg count reduction test with an average reduction of nematode eggs in feces of 43.2% and 60.1% on days 7 and 14 after treatment, respectively. In addition, no toxic effects were noticed during the clinical examination of sheep or by observing blood count and liver or kidney function test results. The obtained results suggest the strong activity of the O. vulgare EO against sheep GINs, probably due to a high percentage of carvacrol (76.21%), whereby it can be considered safe for sheep at the dose tested in vivo. Therefore, it is suitable for use in veterinary practice as a part of an integrated strategy for the control of sheep GINs.