SUMMARY An enzyme-immunoassay was developed to measure the concentration of serum antibody specific for the secretary antigens released by migrating toxocaral larvae. This technique was evaluated by testing sera from healthy UK adults, and from patients with and without toxocariasis. In 922 healthy adults, 2-6 % were found to have elevated specific antibody levels. Elevated values were observed twice as frequently in males as in females but showed no significant regression with age between 20 and 65 years. Of 62 patients with non-toxocaral helminthic infections, all had antitoxocaral antibody levels within the range of values observed in healthy controls and had a mean level which was not significantly elevated. All of 13 patients with clinical toxocariasis had enzymelinked immunosorbent assay (ELISA) antibody levels above the 100th percentiles of both the healthy population and the helminth-infected group and had a significantly high mean value (P < 0.001) more than 12 times that of the healthy or infected controls.The high degree of sensitivity and specificity of the toxocariasis enzyme-immunoassay indicates that this new test should be useful in reference immunodiagnostic applications and in large-scale seroepidemiological surveys.

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Toxocara larval excretions and secretions collected from in vitro culture were used as antigen in passive haemagglutination and soluble antigen fluorescent antibody tests for the diagnosis of visceral larva migrans in experimental animals and man. Antibody to toxocaral secretions was detected in rabbits within 13 days of light Toxocara infection (ten larvae per kg) and within four days of heavy infection (10(4) larvae). Antibody was not detected following infection with 10(4) Ascaris suum larvae. In human sera, antibody was detected at low titre in 1% of 100 healthy adults and in 2% of 50 children. High titres were observed in one third of 170 patients with suspected visceral larva migrans and in 23 of 27 such patients presenting with an eosinophilia greater than 20%. In 25 patients with ocular lesions of an undiagnosed nature, four showed significant levels of anti-Toxocara antibody.

8Platts-Mills TAE, Snajdr MI, Ishizaka K, Frankland AW. Measurement of IgE antibody by an antigen-binding assay; correlation with PK activity and IgG and IgA antibodies to allergens.