Abstract
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.
Highlights
Human toxocariasis is caused by several species o f the nematode round worm Toxocara
The 20 TES-enzyme linked immunosorbent assay (ELISA) negative sera remained negative with A. lumbricoides, T. vitulorum ES antigen and N. americanus larval antigen
This study attempted to determine the cut off ELISA value for a local reference population and to assess the specificity of TES-ELISA, a serodiagnostic test recommended for the diag nosis and seroepidemiological surveys of toxocariasis (4)
Summary
Human toxocariasis is caused by several species o f the nematode round worm Toxocara. Toxocara spp. are common intestinal round worms parasitizing a wide range of domestic, agricultural and wild animals. In Sri Lanka the species include T. canis of dogs and wild canids, T. cati of cats, and T. vitulorum of ruminants. T. canis is very common in dogs throughout the world and is considered as the primary cause o f human toxocariasis (1). Other than in the natural definitive hosts such as the dogs, cats or ruminants, Toxocara spp. cannot develop to the adult worm in humans and other paratenic hosts and in these hosts the development remains restricted to the larval form. The migrating larvae cause extensive damage in the organs involved and the condition, characterized by various clinical manifestations, is known as larva migrans. The highest prevalence rates o f larva migrans is reported in children (2)
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