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.

Effects of high and low temperatures on development time and mortality of house dust mite eggs.

Hatching of Dermatophagoides pteronyssinus eggs was investigated when exposed to temperatures ranging from -70 to +70°C, at varying degrees of humidity (dry and wet heat, direct sunlight) and lengths of time (seven intervals, ranging from 0.5 to 5 h). Exposure to cold was induced using a domestic refrigerator at 4°C, its freezing compartment at -10°C and a deep freezer at -20, -40 and -70°C. For each time interval, there were three slides containing 30 eggs per slide, except for sunlight (five sets of slides). After treatment, all experimental groups were kept on an open work bench for 15 days of observation at ambient room temperature (ca. 22°C) and ca. 75% relative humidity. Control groups with 10 eggs per slide, in triplicate, followed a similar protocol. An egg was considered hatched if an emerging larva was detected from a cracked shell. Results indicated that at 40°C for both dry and wet heat, approximately 80% of all eggs survived. At direct sunlight and dry heat at 50°C, the thermal death point (TDP) occurred at 3 and 5 h, respectively. At 60 and 70°C both wet and dry heat, TDP occurred almost instantaneously. Under cold conditions, only the deep freezer at -70°C was effective in preventing hatching. It may be concluded that exposure to direct sunlight for 3 h, dry/wet heat of 60 and 70°C for a minimum of 30 min, and -70°C prevent egg hatching. This study may have relevance for mite control procedures.

Mite penetration of different types of material claimed as mite proof by the Siriraj chamber method.

BACKGROUND: There are different materials and principles used in the construction of bed encasings. Although these covers claim to have antimite properties, they might not be mite proof. OBJECTIVE: This study evaluated the effectiveness of mite penetration of these covers by using the Siriraj chamber method. METHODS: Thirty-two covers collected from 9 different countries were categorized according to the materials used to manufacture them. They were (1) tightly woven, (2) film or membrane coated and loosely woven, (3) acaricidal coated and loosely woven, (4) nonwoven, (5) film coated and nonwoven, (6) acaricidal coated and nonwoven, and (7) plastic. Adult mites, Dermatophagoides pteronyssinus, were placed on either the outer or inner surfaces of each of the test fabrics for 3 replications, resulting in a total of 6 samples per fabric. All samples were observed for penetration every day for 1 week under a stereomicroscope. If a single mite penetrated any fabric, it was scored as a penetration. RESULTS: Mites penetrated (1) into all samples of film-coated woven and nonwoven covers, an acaricide-coated nonwoven cover, and nonwoven types; (2) from both sides and colonized within the matrix of some samples; and (3) completely in other cases. All of the woven covers and the plastic cover prevented mite penetration. Photomicrographs documented all penetrations. CONCLUSIONS: Tightly woven covers and plastic prevent mite penetration, whereas nonwoven, loosely woven, acaricide-coated, and laminated materials do not. The Siriraj chamber method adequately evaluates the effectiveness of antimite barriers. CLINICAL IMPLICATIONS: For mite avoidance, allergists should recommend the use of tightly woven covers on suspected bedding containing dust mites.