Unusual manifestations of hypersensitivity after a tick bite: report of two cases

Background: Ticks are able to transmit, through biting, various viral, parasitic, and bacterial diseases, the best known being Lyme disease due to Borrelia burgdorferi. In addition, ticks may also induce allergic reactions. Objective: A study of immediate and delayed skin reactions are undertaken to give evidence of an IgE-dependent mechanism. Methods: Two lumbermen reported having had skin reactions following bites by ticks. Skin prick tests and intradermal tests were performed with what was most probably Ixodes ricinus extract in one case. Specific IgE to whole body extract of wood tick were assayed by radioimmunoassay. Histological and immunohistologic examinations of skin biopsy obtained from a pruriginous skin lesion and from a delayed reaction following the intradermal test, were performed. Results: One of them had positive immediate reactions to a prick test and an intradermal test with the same extract. Both patients had significant levels of wood tick-specific IgE antibody as well as elevated serum total IgE levels. Histologic examinations of a pruriginous lesion revealed lymphocytic dermal and perivascular infiltration, with evidence of CD8+ T lymphocytes and Langerhans' cells in the perivascular infiltrates. A biopsy of the place of the delayed reaction following the intradermal skin test also showed the presence of dermal and perivascular lymphocytic infiltrates. Conclusion: IgE-dependent allergy to Ixodes ricinus can explain allergic reactions. Standardized extracts have to be prepared with sufficient amounts of the relevant tick salivary antigens to permit diagnosis by skin and serologic tests of patients, especially lumbermen who may be allergic to Ixodes ricinus.