Allergic reactions, such as urticaria, itching and anaphylactic shock, often complicate the course of cystic echinococcosis (CE). To investigate the role of the IgE-immunoreactive recombinant Echinococcus granulosus elongation factor-1 beta/delta (EgEF-1 beta/delta) in the allergic disorders during CE we determined humoral and cell-mediated responses to this antigen in patients with CE grouped according to the clinical presence or absence of allergic reactions. Immunoblotting analysis showed that serum IgE-binding reactivity to EgEF-1 beta/delta differed significantly in patients with and without allergic reactions (38 of 42, 90% vs. 31 of 56, 56%; P < 10(-4)). EgEF-1 beta/delta induced a proliferative response in 14 of 19 (74%) patients' peripheral blood mononuclear cells (PBMC) irrespective of the allergic manifestations and skewed Th1/Th2 cytokine activation towards a preferentially Th2 polarization. Epitope mapping identified an immunodominant epitope of 18 residues with 78% identity and 89% similarity with an IgE-immunoreactive Strongyloides stercoralis antigen. Overall these findings suggest that EgEF-1 beta/delta is an allergenic molecule that may be a general marker of the intensity of CE immune response and that could lead to a deeper understanding of the specific antigen-induced mechanisms underlying allergic reactions in the human host.