Review Article:1House Dust Mites

Abstract

The most common mites found in the contents of vacuum cleaner sweepings are members of a family of Acaridei, the Pyroglyphidae. Techniques for collecting them effectively were first described in 1964. Since that time, systems for extracting mites from vacuumed dust using sieves and flotation or sedimentation have been improved. The species found in homes are readily cultured. Successful methods utilize high protein foods, an area-enlarging substrate, 25°C and a humidity in equilibrium with saturated NaCl (aw = 0.75, RH = 75%). Development from egg through larva, protonymph, tritonymph to adult requires about a month in cultures under optimum conditions. Pyroglyphids have the reduced setation of parasitic Acaridei but most live as nidicoles. There are 35 species now recognized and 12 of these are associated with man. Dermatophagoides pteronyssinus, D. farinae and Euroglyphus maynei most common on a world basis but other species are significant in some areas, such as Hirstia domicola in Japan. Both D. farinae and D. pteronyssinus have facultative quiescent protonymphs that can survive harsh conditions. These species have a critical equilibrium activity (CEA) below 0.75 and thus can maintain their water content as long as they have access to air as humid as 75% rh during at least part of the time. The favored site for the association of these mites with man is his bed. Populations maintain themselves in beds on a continuing basis. When temperatures and humidities are favorable, these mites also develop in other areas of the house. Their association with man is significant because they either produce or concentrate allergens that are responsible for house dust allergy, which is prevalent on a global basis. In the U. S. it is estimated that 4% of the population is involved. Both mites and house dust can be held at low levels by use of non-fibrous materials and frequent vacuuming. These measures alleviate suffering from house dust allergy. In persistent cases, extracts of house dust or house dust mites have been used in desensitizing patients. House dust mites seem to be resistant to most pesticides, but they are susceptible to low concentrations of lindane.