Clinical cross-reactivity between Artemisia vulgaris and Matricaria chamomilla (chamomile)

Artemisia vulgaris is a common weed and an important source of allergens on the subtropical island of Tenerife, Canary Islands, Spain. It pollinates mainly from July to September, although, due to some local climatic conditions, it may flower throughout the year. Cross-reactivity with hazelnut, kiwi, birch, several Compositae (Ambrosia, Chrysanthemum, Matricaria, Solidago) and grass allergens has been suggested. Few studies have addressed the issue of in vivo cross-reactivity between A. vulgaris and Matricaria chamomilla. The objective of this study was to perform conjunctival and bronchial challenges with A. vulgaris and M. chamomilla and oral challenge with chamomile in 24 patients with asthma and/or rhinitis sensitized primarily to A. vulgaris. Skin prick tests with M. chamomilla were positive in 21 patients. Eighteen patients had a positive conjunctival provocation test with a A. vulgaris pollen extract and 13 patients had a positive conjunctival provocation test with a M. chamomilla pollen extract. Bronchial provocation tests with A. vulgaris were positive in 15 patients and with M. chamomilla pollen in another 16 individuals. Oral provocation tests, conducted with a commercial chamomile infusion were positive in 13 patients. Nine of these individuals were skin test positive to food allergens and 17 to others pollens of the Compositae family. This study confirms a high degree of in vivo cross-reactivity between A. vulgaris and M. chamomilla. Sensitization to A. vulgaris seems to be a primary risk factor for experiencing symptoms after the ingestion of chamomile infusions. Based on the results of bronchial provocation tests, M. chamomilla pollen could be a relevant inhalant allergen.