The almond is a species of Prunus (P. dulcis) belonging to Rosaceae family. The almond differs from other commonly consumed members of this family because its kernel is edible, while the outer pulp is hard and inedible. Allergic reactions to almond have been described, as well as the presence of allergens that are cross-reactive with other plant food allergens, such as peanut or lupine seed proteins, and with grass pollen profilin (1–3). Almond trees are widely distributed in temperate areas of Mediterranean countries, which are also actively involved in the commercial production of almonds. We present a case of occupational asthma developed in a subject chronically exposed to almond shell dust. The patient was a 37-year-old man, an ex-smoker without a personal or family history of atopy. In the last 3 years, he worked as a sheller of hulled almonds in a small almond processing industry. His working place consisted of a 600-m2 normally ventilated room with two shelling machines and two separators. Two years before, he noticed sneezing and nasal discharge a few hours after beginning his working activity. During the last year, he started to have dyspnea, dry cough, and wheezing which were more intense at the end of the work shift and at night. The patient was instead symptom-free during holidays and days off work. He denied any type of reaction after ingestion of foods, including almonds. Physical examination, laboratory tests and chest radiograph were normal.
The almond shell without the hull was pulverized and stored at 4°C overnight. The proteins were extracted using Tris–Hcl pH 7.5 (1 : 5 w/v). Insoluble particles were removed by centrifugation at 15 000 g for 1 h at 4°C. Protein contents were determined according to Bradford (4), and found to be 2.04 mg/ml. The resulting extract was stored at −20°C until required. The extract was applied on 4–12% polyacrylamide precast running gel and stained with 0.1% coomassie brilliant blue. The sodium dodecylsulfate–polyacrylamide gel electrophoresis profile of shell dust extract showed bands ranging from 11 to 14 kDa. Proteins were electrophoretically transferred to a nitro-cellulose membrane (5), which was saturated with 0.1 mol/l tris-buffered saline and 0.5% fat-free milk powder and incubated overnight at 4°C with patient serum. Bound specific IgE were detected by peroxidase-conjugated anti-human IgE antibodies from goat (1 : 1000 in saturation buffer) using the enhanced chemiluminescence kit for Western blotting. Immunoblotting analysis did not show IgE reactivity in the patient’s serum to any band from 11 to 14 kDa. Skin prick tests (SPTs) with food commercial extracts (including those of almonds and other Rosaceae fruits) and diluted extract (1 : 1000, 1 : 100, 1 : 10) of the shell almond dust were performed, using saline solution and histamine (10 mg/ml) as negative and positive controls, respectively. Results of all SPTs were negative. Determinations of specific IgE to aeroallergens, including molds, and Rosaceae members also yielded negative results.
Bronchial testing was performed during a symptom-free period, after 7 days without exposure to almond shell dust. Basal spirometry was normal. Methacholine bronchial challenge was positive [provocative dose producing a 20% fall in forced expiratory volume in 1 s (FEV1): 180 mcg). Specific inhalation challenge with almond shell dust at a concentration of 5 mg/m3 was performed in a challenge chamber according to standardized procedures (6). Serial FEV1 monitoring showed an immediate asthmatic response after 5 min which still persisted 24 h after the challenge.
To the best of our knowledge, this is the first description of occupational asthma because of almond shell dust. Bronchial hyperreactivity was found to be induced by IgE-independent mechanisms.