Sources of insect allergens are diverse and may include skin scales from moths and hemoglobin from lake flies or river flies (Mazur et al., 1987). For domestic cockroaches, fecal material and saliva may contribute to the allergen reservoir, and large quantities of allergen can be washed off the outside of the roach.
The German cockroach Blattella germanica is very common in crowded cities, in the southern United States, and in tropical countries of the world. As early as 1964, Bernton and his colleagues recognized that many patients with asthma who sought treatment at indigent care clinics had skin tests positive for cockroach (Bernton et al., 1964). Positive skin tests have been reported in several urban clinic populations including Boston, New York, Kansas City, Detroit, Chicago, and Washington, D.C. (Call et al., 1992; Hulett and Dockhorn, 1979; Kang et al., 1979). Subsequently, Kang and her colleagues reported positive bronchial provocation and good responses to immunotherapy with cockroach extract (Kang et al., 1979, 1991). In most suburban clinics, few or no patients have positive skin tests to cockroach extracts.
A case-control study of emergency room patients confirmed the significant association of cockroach sensitivity with asthma (Pollart et al., 1989). An unpublished study on cockroach allergen levels in houses in different parts of a town showed that the correlation between cockroach sensitization and asthma was restricted to that part of the town in which cockroach allergen was present in the houses (Gelber et al., in press). Researchers have identified two cockroach allergens, Bla g I (MW ∼ 30 kilodaltons [kDa]) and Bla g II (MW 36 kDa; see Table 3-2), and have developed monoclonal antibodies and assays specific for these allergens (Pollart et al., 1991). Details regarding the sources of these allergens, their cross-reactivity with those derived from Periplaneta americana, and the nature of the particles that become airborne are not well established (Swanson et al., 1985). Cockroach allergen can be found throughout the house, but the highest levels are generally found in kitchens.
Further work is needed to define the nature of insect allergens, the nature of the particles that become airborne, and their role as indoor allergens.
The major outdoor allergens are components of well-defined particles (i.e., pollen grains or fungal spores) that are disseminated by wind and that can be identified microscopically. In contrast, indoor allergens come from a variety of particles that are not naturally airborne and that cannot be identified