Diagnosis of the Early State of Larval Toxoca-riasis Using IgG Avidity

Overview

The term avidity used to express the strength of the bond between a serum specimen and a multi-valent antigen. It is known that the avidity increases with time after antibody challenge andmeasurement of the avidity has been used diagnostically. Recently an assay measuring the IgGavidity of various virus infections and of toxoplasmosis was used to distinguish between acute andchronic infection. Our study was focused on the method to distinguish acute and chronic Toxocarainfection, zoonosis caused by the larvae of dog and cat ascarids Toxocara canis and Toxocara catiknown all over the world for the possibility of provoking the infestation of man, accompanied byvisceral or ocular clinical manifestations.The infection is generally diagnosed by demonstration of specific immunoglobulins to Toxocaraexcretory-secretory antigens (TES) in sera of infected patients. Highly sensitive assays with specificantigens are necessary for detection of antibodies. The test proved clinically useful is the ELISAreaction with TES antigens. This method detects the antibodies for months or even years afterinfection and this is the reason why the discrimination between chronic and recent infection is verydifficult. For disrupting the hydrogen bond urea has been used. The index of avidity was calculatedas the ratio of IgG values in sera treated with urea and the value of IgG in non-treated sera,multiplied by 100. An index up to 40 is considered as low avidity, that means freshly acquiredinfection (36 to 40 borderline) and more than 40 is high avidity.In the group of 1 376 patients only 5.09% low avidities were found. It means that predominantlypatients in the chronic stage of infection attend examination.

Key words:
larval toxocariasis – serology – IgG avidity test.