Studies on the ecology of house-dust mites in wooden houses in Nagoya, with special reference to the influence of room ratios on the prevalence of mites and allergy

Abstract

To examine the influence of housing conditions on the prevalence of house-dust mites and allergy, mite surveys were conducted in bedrooms and living rooms of 22 wooden Japanese-style houses in and around Nagoya City, from September 1983 to June 1984 at about 3-month intervals. Allergic children were found in 11 houses. The mite fauna did not differ much from previous reports : Dermatophagoides farinae and D. pteronyssinus were dominant, constituting 77% of the total mite number, followed by Haplochthonius simplex, Tarsonemidae, Glycyphagidae, Cosmochthonius reticulatus, Cheyletidae, and Acaridae. A significant negative correlation was found between the percentage compositions of D. farinae and D. pteronyssinus : D. farinae had a tendency to increase with the room ratio (the number of rooms in a house to the family size), which was taken as an index of household activities, while the abundance of D. pteronyssinus was not greatly affected by housing conditions. Analyses of interspecies relations and interrelations between housing conditions and mite levels suggested that the house-dust mites could be classified into three groups : Group 1 consists of D. farinae and Oribatei prevailing in houses with high room ratio (>1.3); Group 2 consists of Glycyphagidae, Tarsonemidae and probably Acaridae prevailing in houses with low room ratio (<1.2); Group 3 consists of D. pteronyssinus and Cheyletidae prevailing regardless of housing conditions in wooden houses. The cause of these habitat segregations was considered to be a function of interactions between the humidity requirements in the mites and dampness in the microhabitats influenced by household activities. Simpson's index of mite diversity and the number of allergic children were significantly greater in houses with low room ratio than in houses with high room ratio. Although the number of mites in houses with allergic children was not greater than that in houses with non-allergic children, the diversity index was greater in the former houses. These data suggested a relationship among the prevalence of house-dust mites, allergic sensitization, and housing conditions, particularly room ratio.