An enzyme-linked immunosorbent assay is described for the detection of serum antibodies to visceral larva migrans (Toxocariasis). Excretory-secretory antigens of the second-stage larvae of Toxocara canis were used as antigen to coat the polystyrene plates. With sera from patients high antibody titers were observed in both ocular and visceral disorders. Cross-reactions due to other parasitic infections could be excluded, including other migrating larval infections such as ascariasis, trichinellosis, strongyloidiasis, filariasis, and anisakiasis. In a small seroepidemiologic survey of healthy primary schoolchildren, a remarkably high percentage (7.1) reacted positively to this method. These children showed eosinophilia as compared to the seronegative group. The data were compared with those observed in other countries and the results prompt reconsideration of the significance of T. canis for public health.

With an enzyme-linked immunosorbent assay antigen, specific circulating immune complexes (CIC) were demonstrated in experimental and human toxoplasmosis. In experimentally infected mice, CIC became demonstrable as soon as antibodies appeared after fatal infection. When a nonvirulent strain of Toxoplasma was used CIC remained detectable for several weeks. This period was characterized by clinically healthy animals with increasing antibody titers and by cysts growing in the brains of the animals, indicating a subacute stage of the toxoplasma infection. In the human sera, a surprisingly high percentage of CIC was demonstrated. Both immunoglobulin G (IgG) and IgM were found in the CIC; however, IgG was seen in the majority. If the humans were grouped according to other serological results, such as a combination with IgM antibodies, circulating antigens, or both, or a positive complement fixation test, increasingly more CIC were observed. When sera were selected from patients with clinical symptoms generally associated with toxoplasmosis, more CIC were also again demonstrated. On the contrary, in healthy individuals (blood donors), CIC were also regularly observed, suggesting that exacerbations of latent infections or reinfections may regularly occur without leading to clinical signs. In conclusion, we propose that the interpretation of a positive CIC test requires great care but may provide useful information about the activity of a toxoplasma infection.

The combination of three parameters (IgG, IgM and circulating antigen) in a so-called 'ELISA triple test' was suggested for advantageous diagnosing of human toxoplasmosis. A qualitative assay was used with the following arbitrary assumptions: IgG antibodies reflect an infection, IgM antibodies reflect a recent (primary) infection and circulating antigens reflect an active infection. The three assays were performed simultaneously in one microtiter plate. This approach was tested with 1091 patient sera submitted for routine diagnosis. In comparison with conventional indirect immunofluorescence and complement fixation test it was observed that combinations indicating a recently acquired infection (combinations with IgM and/or circulating antigen) mainly paralleled low or negligible conventional antibody titers. No strict association was seen between particular combinations and certain clinical symptoms suggestive for toxoplasmosis. In conclusion it was stated that the triple test for support of clinical diagnosis has some advantages but that a strong need exists to be able to demonstrate exacerbation or reinfections which are generally not characterised by IgM antibody formation of free circulating antigens but may be the reason for elevated conventional antibody titers.

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