• fern;
  • immunoblotting;
  • occupational;
  • Polypodium vulgaris;
  • spores

Although fern allergy is common in some countries, it is rare in Spain, where, so far, fern antigens have not been recognized as occupational allergens.

An 18-year-old man was diagnosed with mild rhinoconjunctivitis and asthma to pollen, mites, and cat dander. Several months later, he began to work at a fishmonger's, when he noted worsening of his rhinoconjunctivitis. He also developed local pruritus and wheals after handling the fern fronds (Polypodium vulgaris) used to decorate boxes of fish.

The patient rarely suffered nasoconjunctival symptoms when not at his workplace. Symptoms did not worsen on contact with any fish, and he ate them without problems. Rhinoconjunctivitis and contact urticarial symptoms totally disappeared when the ferns were removed from his workplace.

Prick by prick test with the fern was positive (5×8 mm wheal). Seven control subjects were negative.

Extract of fern frond was prepared in our laboratory and for in vitro studies. Specific IgE to fern was detected by ELISA in the patient (optical density [OD]: 0.656), and it was negative in a control subject (OD: 0.096). SDS–PAGE followed by immunoblotting revealed specific IgE antibodies in the patient's serum against 12- and 35-kDa antigenic bands.

Fern spores, which are released under optimal conditions of humidity and temperature (1), probably cause allergic reactions as aeroallergens as well as contact sensitizers. Our patient developed both types of reactions. Fern spores are important environmental allergens in tropical countries, where they may be the third-most common aeroallergen (e.g., Thailand and the Philippines) (2). The incidence of sensitization to fern spores (prick test with self-made fern extract) in Asian countries is close to 65% among patients with asthma and/or rhinitis, and 25% among nonatopic subjects (3). Bunnag et al., performing nasal provocation tests in fern-sensitized patients with fern-spore extract, found positive results in 70% of the patients (2). Geller-Bernstein et al. (4) found that 50% of fern-sensitized, atopic subjects had had an ornamental fern at home for 3–5 years.

Kofler et al. (1) present a patient who reported rhinitis due to a different fern genus (Nephrolepis sp.). Immunoblotting analysis revealed specific IgE antibodies to 40- and 35-kDa proteins. The 35-kDa protein may be a common allergen among fern species, because our patient's serum IgE recognized a protein with the same molecular mass as in P. vulgaris.

We describe the first known case of occupational rhinoconjunctivitis and contact urticaria caused by an ornamental fern.


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