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.
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 cm 3 /sec/cm 2 , a thread count ≥ 246/in 2 , and a pore size of 2-10 µm.
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