Measurement of the IgG Avidity Index in the Diagnosis of Clinical Toxocariasis Patients

Toxocara spp. are parasitic nematodes responsible for human toxocariasis, a common zoonotic helminth infection. The five main features of human toxocariasis are the classical ocular toxocariasis and visceral larva migrans syndrome, followed by covert toxocariasis, common toxocariasis and neurotoxocariasis. The diagnosis of toxocariasis is feasible by considering clinical symptoms, anamnestic history and serology laboratory results; however, serological criteria cannot be used to distinguish active Toxocara infection from past exposure, which is an area of much discussion in clinical practice. In this context, we developed avidity tests (ELISA and immunoblotting) and evaluated their clinical usefulness in distinguishing past from active toxocariasis. Our study involved 46 patients divided into two groups: active toxocariasis (n = 14) and chronic toxocariasis (n = 32). According to the avidity indices obtained for both the chronic and active toxocariasis groups, we proposed two thresholds: first, an AI lower than 32% supports an active infection; secondly, a threshold above 42% can exclude an active infection. In order to use this assay in routine clinical practice, however, is still requires standardisation with regards to the method and threshold values, which can be established through studies involving larger populations.

Automated summary

Toxocara spp. are parasitic nematodes that cause human toxocariasis, with five main features including ocular toxocariasis, visceral larva migrans syndrome, covert toxocariasis, common toxocariasis, and neurotoxocariasis. Diagnosis is based on clinical symptoms, history, and serology, but distinguishing active infection from past exposure remains a challenge. A study on avidity tests showed potential for differentiation, but further standardization and larger studies are needed for routine clinical use.