[Factors influencing the house dust mite population IV. Altitude]

A study has been carried out on house-dust mites present in the buildings of 3 towns in Catalunya (Spain), with different altitudes: Reus (altitude, 76 m); L'Ametlla (altitude, 321 m); and Puigcerdá (altitude, 1.202 m). The period studied was between october, 1975 and september 1976. From this study, a negative correlation has been observed between the number of mites in house dust and the altitude of the town. This supports the results obtained by other authors. The decrease in the number of mites with increases in altitude is due to a decrease in the number of mites belonging to the Pyroglyphidae family. This family was present in all samples of house-dust studied, and generally in a greater number than other groups of mites. Of the three species of Pyroglyphidae more frequently present in house dust (Dermatophagoides pteronyssinus, D. farinae and Euroglyphus maynei), D. pternyssinus was the most abundant as well as the most affected variations of R.H and temperature resulting from the variations of the altitude. D. farinae and E. maynei were found in low levels suggesting inadequate conditions of temperature and R.H. in the houses studied. Even if E. maynei was the most abundant species in Puigcerdá, this is due more to the decreased incidence of D. pteronyssinus than to an increase in the number of E. maynei.