LONG TERM EFFICACY OF ACARICIDES AGAINST HOUSE DUST MITES (DERMATOPHAGOIDES PTERONYSSINUS) IN A SEMI-NATURAL TEST SYSTEM

Abstract:
House dust mites are together with pets the most important source of allergens in dwellings in western Europe. In a recently developed semi-natural test system, mites may be studied in an environment comparable to the dwelling situation. In this laboratory test, it should also be possible to determine the efficacy of intended measures against mites in dwellings. In the present study three acaricidal products were tested: Acarosan powder formula (Allergopharma J.Ganzer KG, Reinbek / Hamburg, Germany), Allersearch BT (Allersearch, Granville, New South Wales, Australia), and Tymasil (Gist-Brocades NV, Delft, The Netherlands). All three products have been employed in dwellings with more or less positive results. On soiled mattress models 50 house dust mites (Dermatophagoides pteronyssinus) were incubated and exposed to one of the three products. The surviving population after two different periods was determined by counting mite numbers following a heat escape method. In untreated blanks, mites developed from 0.5 mite per cm2 to 1.6 mites per cm2 in 8 weeks and to more than 30 mites per cm2 in 24 weeks. After 8 weeks 99% of the mites were killed by Acarosan, while Allersearch and Tymasil proved less effective. The relative efficacy of each product after 8 week incubation correlates well with the results obtained in dwellings. However, when incubation is prolonged after treatment with Tymasil or Acarosan, the mite populations appeared to revive in considerable numbers, especially after treatment with Allersearch. From these results it appears that Tymasil is not an effective acaricide on soiled materials. While Acarosan and Allersearch BT decimate the populations in a one-hit treatment, neither is capable of keeping the number of house dust mites on mattresses low for 6 months. However, a first application of either of these products in late winter, when mite numbers are low in general, with a repeat after 2 or 3 months, should be sufficient to keep mite numbers low for the whole mite season.