Toxocariasis in internationally adopted children: Seroprevalence, diagnostic and therapeutic strategies.

OBJECTIVES

To evaluate the seroprevalence of Toxocara spp. infection among internationally adopted children and to assess the diagnostic performance og IgG-TES-ELISA test compared with IgG-TES-WB test. Furthermore, to determine wether a dual-step diagnostic strategy approve diagnostic accurancy and reduces unnecesary second-level investigations and albendazole therapy.

METHODS

We performed a retrospective study of all internationally adopted children consecutively evaluated at the Infectious Diseases Unit of Meyer Children's University Hospital between 2009 and 2025 as part of the standardized "Adopted child screening." Two diagnostic approaches were used: a one-step protocol based solely on IgG-TES ELISA (2009-2017) and a two-step protocol integrating ELISA with confirmatory IgG-TES Western blot (2018-2025). Clinical characteristics, eosinophil counts, co-infections, second-line diagnostic procedures, and treatment decisions were systematically reviewed.

RESULTS

Among 2657 children screened for toxocariasis, 2085 underwent the ELISA-only approach, 370 resulted positives. From 2018 onward, 572 children were tested, with 92 ELISA-positive results; 68 were confirmed by Western blot. Overall, second-line investigations and treatment were required more frequently in the ELISA-only group than in the combined protocol group (P = 0.002). Using Western blot as reference, ELISA exhibited high sensitivity (95.8%) but modest specificity (67.1%). Most seropositive children were asymptomatic or displayed covert toxocariasis, with only one visceral case identified. More than one-third of children with eosinophilia were seropositive for Toxocara spp.

CONCLUSIONS

Approximately one in six internationally adopted children shows Toxocara spp. seropositivity. While IgG-TES ELISA is a sensitive screening tool, confirmatory Western blot substantially improves specificity and diagnostic stewardship, reducing unnecessary second-level investigations. A substantial proportion of seropositive children likely represent clinically inactive seropositivity, for which it is not possible to differentiate recent infection from past exposure to the parasite. Integrating serology with eosinophil counts, IgE levels, and clinical assessment is crucial to distinguish active from resolved infection and to identify children who require clinical and instrumental follow-up and albendazole therapy, thereby avoiding unnecessary interventions.