Crude extracts of the thermophilic actinomycetes commonly associated with hypersensitivity pneumonitis are produced in a manner similar to that described for the fungi. They are used in double-diffusion assays to evaluate the presence or absence of specific IgG antibodies (precipitins).
The protozoa are microscopic animals that occupy reservoirs similar to those of the bacteria. Intact protozoa are generally too large to remain in the air for long periods of time, although occasionally they cause infection of the eye and brain when introduced into the eye or respiratory tract in large droplets (e.g., those produced by hot tubs). Some protozoa in indoor water reservoirs excrete allergenic material that can become airborne if droplets form. Acanthamoeba polyphaga and Naegleria gruberi allergens have been associated with humidifier fever and work-related asthma (Finnegan et al., 1987).
The algae are plantlike organisms with rigid, cellulosic cell walls; for the most part, they live in aquatic environments. Vegetative cells of the microscopic algae can be relatively abundant in outdoor air near bodies of water that support luxuriant algal growth (Schlicting, 1969). They have been reported to cause IgE-mediated allergy, but this question has not been well studied (Mittal et al., 1979).
The slime molds (Myxomycetes) are microorganisms that do not fit well into such classifications as ''plant" or "animal." They are motile amebae during part of their life cycle, but at another juncture they become immobile and produce spores that are indistinguishable from those of some fungi. These small but visible organisms occupy niches in the environment that are similar to those of some fungi (e.g., on damp organic material), and their spores form a small part of the outdoor aerosol. There is some evidence that these spores are sensitizing (Giannini et al., 1975; Santilli et al., 1990).
Environmental control strategies are intended to reduce airborne concentrations of allergens. Several current strategies and methods are designed