Validation of a Toxocara ES antigen Enzyme Linked Immunosorbent Assay (TES-ELISA) for use in childhood toxocariasis in Sri Lanka

An enzyme-immunoassay detecting serum antibodies specific for excretory secretory antigens of Toxocara L2 larvae, a test recommended for seroepidemiolgoical studies, was validated for use in a local population of children under 12 years. The cut off level, at antigen dilution of 1 Oug/ml and serum dilution of 1:100, determined by I tail confidence limit of 1.96 was 0.148 with a geometric mean of0.16087. This conforms to the standard reference value for this test (OD=0.2) adopted in reference laboratories in other countries. The upper OD value of 0.7 accepted in these reference laboratories to indicate recent exposure or active infection corresponded to the 84111 percentile in our population. Cross reactions were not seen against Ascaris lumbricoides L2 larval excretory secretory antigen and L3 larval antigen of Necator americanus. However, 25% of the positive sera cross reacted with T. vitulorum, the common buffalo parasite in Sri Lanka. This indicates that development and validation of species specific tests is essential for determining the role of each species of Toxocara in the etiology of human toxocariasis in Sri Lanka.