Vanna Mahakittikun

Killing mites with heat

. HOUSE-dust mites may be effectively killed by high temperatures (1±3). We sought to investigate the effects of various forms of heat deliverance to household items at varying temperature upon the survival of house-dust mites. Cultures of Dermatophagoides pteronyssinus were used in four separate sets of experiments. In experiment 1, mites were plated in Petri dishes, and the effects of dry heat (incubator heat) and wet heat (hot water) at various temperature settings (40, 50, 60, and 708C) at 10, 20, 30, and 40 min were examined. In experiment 2, the effect of exposure to dry heat upon the behavior of mites placed in polyester membrane was examined. In experiment 3, we examined the effect of dry heat applied by ironing upon live mites placed on a cotton sheet and on a comforter of 2.5 cm in thickness. Temperatures at various ®ber layers of the comforter were measured. Mites were examined at various layers of comforter ®ber layer. Experiment 4 was set to examine the effect of sunlight and of vacuum-cleaning upon live mites seeded on to a straw mat. The survival of mites was determined by examining their shape and mobility. All experiments were performed in triplicates. The combination of a temperature of 508C or over with a duration of 20 min or more was suf®cient to cause 100% death of mites by dry heat. For wet heat, a temperature of 608C or over for 20 min or more was required to kill all mites. Mites were found to migrate into deeper layers of polyester ®ber in response to dry heat. Dry heat applied via ironing (408C for 5 s) killed all mites on a cotton sheet and on the top two ®ber layers of a comforter. Mites could survive this process in deeper layers of the comforter (40% and 93% in the third and fourth ®ber layers). Direct sunlight for 6 h, vigorous shaking, and vacuum-cleaning of the straw mat were not effective to kill or remove mites from the mat since mites could hide in the cracks or cling very tightly to mat ®bers. In our experiments, dry heat seemed to be more effective than wet heat. With a hot wash of over 608C, a duration of more than 20 min is necessary to kill all mites. Ironing is effective for killing mites on thin sheets, but not on thick clothes or comforters. A straw mat supports the survival of mites well and should not be used by mite-sensitive individuals.

Anti-mite Covers: Potential Criteria for Materials Used Against Dust Mites:

There are many types of material used to construct bedding encasing for dust mite and allergen protection, but relatively few have been evaluated for their anti-mite properties. This study surveyed the anti-mite/allergen properties and physical characteristics of covers with a view towards establishing potential parameters for evaluating the efficacy of such encasings. Fifty-three covers advertised as mite-proof were randomly purchased from local markets found in ten different countries. All fabrics were evaluated for their ability to block the movement of allergens and live mites. Air permeability, dust leakage, and thread count, where applicable, were also measured. The major finding was that plastic and the tightly woven covers completely prevented mite penetration while exhibiting > 99 % allergen impenetrability. The film-coated fabrics, the mixed type, and the acaricidal-coated non-woven were successful in blocking allergens, but were commonly observed to allow some mite penetration. For the tightly woven fabrics, dust leakage and air permeability were minimal, while thread count was uniformly high. Cotton bed sheets were completely penetrable by mites and allergens. Overall, allergen impenetrability was negatively associated with dust leakage, thread count, and air permeability. Thread count also exhibited inverse relationships between dust leakage and air permeability. Dust leakage and air permeability were positively associated. The optimal characteristics for effective encasings include tightly woven covers with allergen impenetrability > 99 %, resistance to live mite penetration, dust leakage of < 4 %, air permeability between 2 and 6 cm3/sec/cm 2, a thread count ≥ 246/in2, and a pore size of 2—10 µm.

Laboratory assessment of the efficiency of encasing materials against house dust mites and their allergens

Background: The current recommendation to reduce mite allergen exposure for mite‐sensitive individuals is to use allergen‐impermeable bed coverings. As these covers are made of various kinds of materials, they vary in quality. The objective of this study was to investigate the efficiency of different covering materials against house dust mites and their allergens in vitro.