Evaluation of Trichinella cross-reactions in the serological diagnosis of toxocariasis

Toxocariasis caused by the nematode larvae of the Toxocara genus is a worldwide parasitic zoonosis. Diagnosis of human toxocariasis commonly relies on serological tests since the symptoms and signs of Toxocara infection are not pathognomonic. However Toxocara larval excretory-secretory (TES) antigen used in serological tests may exhibit low specificity due to the cross-reactions between related helminth infections such as ascariasis, anisakiasis, strongyloidosis and filariasis. In this study, we aimed to evaluate the possible effect of Trichinella cross-reactions in the serological diagnosis of toxocariasis by using ELISA and Western blot (WB) assay. For this purpose, sera samples of 209 trichinellosis patients who were definitely diagnosed during the Trichinella britovi outbreak occurred in İzmir in January 2004, were used. All the samples were screened initially by commercial Toxocara IgG-ELISA kit (Cypress Diagnostics, Belgium), then commercial Toxocara IgG-WB (Test-Line Diagnostics, Czech Republic) was applied to positive/ borderline-positive sera for confirmation. In our study, 94.3% (197/209) of the sera were found seronegative, while nine were positive and three were borderline. Thus a total of 12 (5.7%) sera were considered as seropositive by Toxocara IgG-ELISA. According to the results of WB, only one sera with the antigenic bands of 120 kDa, 32 kDa and 26 kDa in molecular weights was evaluated as positive. Four sera samples were found to be borderline. In three of border sera, the antigenic bands of 120 and 70 kDa in molecular weights were observed together and one sera had three (120, 70 and 32 kDa) different antigenic bands. Seven sera that had been found to be positive by ELISA was considered as negative by WB. While no bands was observed in four of these, three samples had an antigenic band of 120 kDa which had no diagnostic value when it was found alone. The results of our study showed that the crossreactivities between anti-Trichinella antibodies and TES antigens may be observed during Toxocara IgG ELISA assay. For that reason the positive Toxocara IgG-ELISA result should be confirmed by different tests such as WB for the definitive diagnosis of toxocariasis.