A preliminary study of the acaricidal activity of clove oil, Eugenia caryophyllus.

BACKGROUND The search for more eco-friendly acaricides has prompted testing of medicinal plants from botanical sources. OBJECTIVE To evaluate the eradication of house dust mites (HDM), Dermatophagoides pteronyssinus, by direct contact using the essential clove oil (Eugenia caryophyllus). METHODS A pilot study was initiated to determine the killing power of clove oil. Synthetic fibers were immersed in 2% clove oil for 30 min, dried in a hot air oven at 60°C for 2 hrs after which 0.5 gm of HDMs were exposed to these coated fibers placed in the Siriraj Chamber (SC). Two additional long-term methods were employed. Ten mites were placed in the SC and 10 μl of clove oil was pipetted or sprayed onto them. These latter two procedures were each carried out for 3 consecutive days at 0, 1, 3 and 6 months. The solutions antimicrobial and antifungal properties were evaluated by exposing common bacteria and fungi to sterile filter disks impregnated with the mixture, and after overnight incubation, the disc diffusion method on nutrient agar was used. Ethyl alcohol served as the placebo. 99% and 81%, respectively, while the placebo mortality was <5%. The zone of inhibition indicated significant clearance for all the bacteria and fungi indicating greater biocidal activity when compared to the controls. RESULTS SEMs revealed dead mites on the fibers. The effectiveness of pipetting and spraying was 99% and 81%, respectively, while the placebo mortality was <5%. The zone of inhibition indicated significant clearance for all the bacteria and fungi indicating greater biocidal activity when compared to the controls. CONCLUSIONS Clove oil is a promising agent for killing dust mites with a potential use in dust-mite laden mattresses. Spraying diminishes in efficiency after 3 months.