been identified in dust from the walls and air-conditioning filters of rooms in which mice are housed. Airborne allergen concentrations ranging from 1.8 to 825 ng/m³ of air have been detected; concentrations vary with both the number of mice and the degree of work activity in the room (Twiggs et al., 1982). Mouse urinary allergenic protein has been found in air samplings from inner-city dwellings (Swanson et al., 1985), but the effects of this exposure on the health of inhabitants are not known.

Guinea pig allergens are present primarily in the urine. At least two major allergenic components have been identified. Air sampling studies may show varying concentrations of the urinary protein in the air, depending on the number of animals. Most allergenic activity in the air is associated with particles in two size ranges: those less than 0.8 μm in diameter and those greater than 5 μm (Swanson et al., 1984).

Occasionally, hamsters and gerbils may account for allergic symptoms. Positive skin tests to hamster dander extracts have been reported among laboratory workers, and gerbil extracts prepared from serum and hair/epithelium have produced positive skin tests in sensitized patients. Allergens from these rodents have not been characterized further. Even less fully characterized are rabbit allergens. The major known allergen is obtained from fur extracts and saliva (Warner and Longbottom, 1991).

Control measures for laboratory workers include the use of protective clothing and appropriate respiratory protection. Source control measures involve placing filter caps on animal cages, increasing the frequency of air exchange (including 100 percent exhaust of the animal room with no recirculation), locating exhaust ducts at floor level, increasing the frequency of removal of animal waste and bedding, and using high-efficiency filters to provide filtered laminar flow air. Because of the high rate of production of rat urinary protein allergens, very high air exchange rates are required to substantially reduce allergen levels in rooms that house a large number of animals (Swanson et al., 1990).

The prevalence of sensitivity to cattle is unknown; however, two major allergens from cattle with molecular weights of 20 and 22 kDa have been identified (Ylönen et al., 1992). These allergens are derived from cow hair and dander, but the 20-kDa allergen is also found in urine. Immunochemical assays for quantitating cattle allergens in cow-shed air samples have shown concentrations ranging from 137 ng/m³ to 19.8 μg/m³ (Virtanen et