FARM-WORKERS OCCUPATIONAL ALLERGY TO TETRANYCHUS-URTICAE - CLINICAL AND IMMUNOLOGICAL ASPECTS

A group of 46 farm workers (32 men), affected by a recurrent ''occupational disease of undetermined origin'', underwent an immunologic investigation with a Tetranychus urticae (TU) whole-body extract (TU-WBE) prepared in our laboratory. The patients suffered from seasonal attacks of rhinitis, during the summer and autumn periods, when working in open fields (30 subjects) or in greenhouse flower cultivation (16 subjects). In most patients, rhinitis was associated with bronchial asthma (16 subjects), urticaria (14 subjects), or both (three subjects). Allergic alveolitis or other common allergic diseases had been excluded, and a diagnosis of ''occupational disease of undetermined origin'' had been made before by other medical centers. Ten healthy farm workers and 10 atopic townsmen were chosen as control groups. An in vivo and in vitro diagnostic trial by skin prick testing (SPT) and serum specific IgE dosage with TU-WBE were done in all subjects. Thirty-six patients (78%) were found to be positive to both SPT and the IgE enzyme allergosorbent test (EAST), with a good correlation between IgE serum levels and cutaneous wheal size. Control groups did not show any reaction. The IgE-EAST homologous inhibition test was positive. The IgE-EAST cross-inhibition test excluded cross-reactivity between TU and Dermatophagoides pteronyssinus. The TU-exposure test was positive for the 36 patients with TU-WBE-specific IgE. Three patients who were negative for TU-WBE-specific IgE reacted to the TU-exposure test; in these patients, the scratch-chamber test (Finn chamber) with eggs and droppings from TU was positive. We suggest the possibility of a TU allergy also in those subjects in whom clinical symptoms can be attributed to other common allergens.