Allergy and parasites reevaluated: wide-scale induction of chronic urticaria by the ubiquitous fish-nematode Anisakis simplex in an endemic region

Abstract

Background The ubiquitous fish-nematode Anisakis simplex produces acute urticaria or angioedema in the course of gastro-allergic anisakiasis. We studied the relationship between this nematode and chronic urticaria (CU), as well as the clinical usefulness of measuring specific IgG 4 in A. simplex-sensitized patients with CU. Methods First, the prevalence of sensitization to A. simplex was estimated in 135 consecutive CU patients and the result was compared with known data about sensitization in a healthy population. Then, clinical response to a 2-month diet without fish was analyzed in 76 CU patients. The improvement rate in patients with and without sensitization to A. simplex was compared. Finally, the improvement rate, other clinical data and specific immunoglobulins in sensitized patients with and without detectable specific IgG4 were compared. Results a) The A. simplex sensitization rate in CU patients was 52.6 % compared with a known prevalence of between 16 and 20 % in our region. b) Of 65 sensitized patients, 52 experienced clinical improvement after the diet compared with only three of 11 patients without sensitization to A. simplex (p = 0.001). c) Of 43 patients with detectable specific IgG 4, 38 showed clinical improvement compared with only 14 of 22 patients without detectable IgG 4 (p = 0.02). Eight of nine patients with previous fish-associated cutaneous symptoms had detectable specific IgG4 compared with 15 of 32 patients who reported no previous fish-associated symptoms or acute urticaria (p = 0.03). Conclusions Our results indicate that A. simplex is a possibly widespread etiologic agent able to induce CU. This parasite model constitutes the first report that associates an infectious agent with CU on a large scale. The detection of IgG 4 antibodies reflects a previous acute parasitic infection and a temporary diet without fish improves symptoms in most patients with detectable specific IgG 4.