WORK-RELATED RESPIRATORY ALLERGY ASSOCIATED WITH SENSITISATION TO STORAGE PESTS AND MITES AMONG GRAIN-MILL WORKERS

Background: Exposure to grain dust is associated with a number of adverse allergic health outcomes including conjunctivitis, rhinitis, urticaria/dermatitis and asthma. These clinical manifestations are the result of a multitude of allergens and bioactive materials present in the grain dust. The aim of this study was to assess the patterns of sensitivity to various storage pests among grain mill workers and their relationship to work-related respiratory symptoms and asthma. Methods: This is a sub-study of the cross-sectional study previously conducted on 111 workers employed in a grain mill in Cape Town. The study instruments included a questionnaire based on the American Thoracic Society (ATS) questionnaire, and specific IgE determinations on serum obtained from workers. Blood samples were analysed by ImmunoCAP using the UniCAP (R) System (Pharmacia Diagnostics AB, Uppsala, Sweden) for house-dust mites (Dermatophagoides pteronyssinus, Dermatophagoides farinae), storage mites (Blomia tropicalis, Lepidoglyphus destructor and Tyrophagus putrescentiae), cockroaches (Blatella germanica, Periplaneta americana, Blatta orientalis), beetles (Tenebrio molitor, Sitophilus granarius) and mould (mouldmix - Penicillium notatum, Cladosporium herbarum, Aspergillus fumigatus, Alternaria alternata). According to the ImmunoCAP scoring system, a positive score was any value greater than 0.35 kU/l. Results: Among this group of 111 workers, the majority (89%) were men and 49% smokers. The prevalence of IgE reactivity to house-dust mite (41%) was very similar to reactivity to at least one grain-dust allergen (42%) viz. cereal grains, insects and mites. Reactivity patterns to storage mites were similar to wheat (26%), while the prevalence of reactivity to cockroach (B. germanica) similar to rye (22%). Storage mite, B. tropicalis, produced the strongest IgE response (mean IgE=7.85 ku/l). Beetles such as grain weevil (16%) and mealworm (13%) produced a lower proportion of sensitised individuals, with the latter producing a stronger immune response (mean IgE=2.32 ku/l). Among the cockroaches, B. orientalis appeared to generate the strongest immune response. Very high statistically significant linear correlations (Spearman r = 0.75-0.9) were found between dust mites and storage mites, and between cockroaches and beetles, indicating the existence of similar allergens. Among the group of grain-mill workers studied, the prevalence of work-related asthma symptoms such as wheeze and tight chest was 13% and 5% respectively, while 7% of workers were being treated for doctor-diagnosed asthma. IgE reactivity to mealworm (T. molitor) was significantly (p<0.05) associated with work-related asthma (wheeze) as were cockroach species (B. orientalis) in atopic workers ( workers with elevated IgE reactivity to house-dust mite). Conclusion: Allergens from storage pests (mealworm and cockroach) in grain-mill dust is a significant predictor of work-related asthma symptoms. This is a particularly evident in atopic workers who demonstrated increased IgE reactivity to mealworm (Tenebrio molitor) and cockraoch ( B. orientalis) associated with work-related asthma symptoms.