Tetranychus urticae allergy in a population without occupational exposure

Tetranychus urticae is a phytophagus mite found in the leaves of numerous plants. High sensitization rates have been demonstrated, however, provocation tests have only been performed in an occupational setting.

To assess accuracy of skin prick tests and clinical relevance of T. urticae sensitization by means of conjunctival provocation tests (CPT) in a population without occupational exposure and to evaluate possible environmental risk factors for T. urticae allergy.

Patients ≥ 18 years old sensitized to T. urticae (n = 12) and a non-sensitized control group (n = 12) were invited to perform CPT with T. urticae and fulfill a questionnaire including demographic data, questions on environmental exposure to T. urticae and allergy symptoms/diagnosis. A single-blinded placebo-controlled CPT with T. urticae (Leti®) was performed with increasing concentrations (0.002, 0.02, 0.2 and 2 mg/mL) and considered positive if conjunctival hyperemia, palpebral edema or lacrimation were observed in the tested eye.

Of T. urticae sensitized patients (mean wheal 4.4 ± 1.5 mm), 9 had a positive CPT, including 3 monosensitized. A good diagnostic accuracy was found for skin prick tests: AUC = 0.952, sensitivity = 100%, specificity = 80%, positive likelihood ratio = 5 and negative likelihood ratio = 0 for a 3 mm wheal. No differences were found between allergic and non-allergic subjects regarding atopy, allergic disease or farming activities.

A high prevalence of allergy to Tetranychus urticae was found in the north of Portugal. Future studies with a larger number of patients are needed to evaluate its relation to clinical symptoms and the impact of environmental factors.