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

Estelle Menu,Léa Luciani,Sophie Legrand,Coralie L’Ollivier,Lora Kopec

doi:10.3390/pathogens10091086

Abstract

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.

Highlights

Toxocara canis and Toxocara cati are parasitic nematodes responsible for human toxocariasis, a common zoonotic helminth infection
Some studies have suggested determining the avidity using the immunoblot technique to discriminate between antigens related to high-avidity antibodies from those related to low-avidity antibodies in strongyloidiasis and Q fever infections [9,10]. Based on these established practices regarding the use of urea for avidity tests, we developed avidity tests (ELISA and immunoblotting) and evaluated their clinical usefulness to distinguish past from active toxocariasis
Nine patients in the active toxocariasis group had an avidity index (AI) value lower than 32%, while in the chronic toxocariasis group only one patient had an AI value lower than 32%

Summary

Introduction

Toxocara canis and Toxocara cati are parasitic nematodes (roundworms) responsible for human toxocariasis (larval toxocariasis), a common zoonotic helminth infection. The seroprevalence estimates range from 5 to 15% in the United States, reaching up to 80% in children in parts of Nigeria [2,3]. This neglected disease usually occurs in children because they often play in areas containing contaminated soil. Stray and domiciliated dogs and cats play an important role in the transmission of Toxocara spp. by providing environmental contamination opportunities, which perpetuates the spreading of the infection among human populations [4]. Humans are paratenic hosts who become infected by ingesting infective eggs in contaminated soil, in raw vegetables or other foods, and possibly from contact with dog or cat hair [5]. The five main features of human toxocariasis are classic ocular toxocariasis (OT) and visceral larva migrans (VLM)

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