Background: Human toxocariasis is a common, worldwide helminthozoonosis that may elicit syndromes including various allergy symptoms. The diagnosis relies upon specific serology. However, this parasitosis is often self-limiting, and many subjects have residual antibodies, thus making differential diagnosis quite difficult when blood eosinophilia, a commonly accepted criterion of active helminthiasis due to tissue-dwelling parasites, is lacking.
Methods and results: We present a patient with chronic irritant cough displaying negative allergologic screening, normal blood eosinophilia, but positive toxocariasis immunodiagnosis. Therefore, this case presented the fortuitous association of an unexplained allergic picture with residual anti-Toxocara antibodies. In an attempt to distinguish between active and past toxocaral infection, the subject's level of eosinophil cationic protein (ECP) was assessed and then compared to those of four control groups, namely, healthy volunteers, subjects presenting anti-Toxocara residual antibodies, patients with various helminthiases, and patients with active toxocaral disease. Since the patient's ECP level was found to be sharply elevated, we hypothesized that viable Toxocara larvae were still present in the tissues, and the patient was given anthelmintic therapy. At the control checkup, the cough had waned and the ECP level had decreased to below the mean value observed in both healthy subjects and in subjects with past toxocaral infections.
Conclusions: These data suggest, first, that patients presenting unexplained allergic syndromes should be checked for helminthiases, even if blood eosinophilia is lacking, and, second, in such subjects displaying positive toxocariasis immunodiagnosis, ECP assessment would be a useful marker to distinguish between active and past toxocaral disease.