Larva-specific antibodies in patients with visceral larva migrans.

Seven of 10 patients with visceral larva migrans (VLM) had serum precipitating antibodies specific for larval antigens of Toxocara canis as determined by double diffusion in agar. Such antibodies were absent in 114 normal adults and 25 patients with collagen disease. Precipitation of ascarid components by C-reactive protein resulted in false-positive reactions, but this precipitation was readily prevented by appropriate absorption of sera before testing. A more sensitive assay, the enzyme-linked immunosorbent assay, revealed high titers of antibodies to larvae of Toxocara in all patients with VLM; the log2 titer ranged from 9 to 14. Five of eight household relatives of these patients and four children who had had VLM two to four years before testing had titers of 6-12. Of the 114 normal adults, 105 had titers of 0-2; nine had titers of 3-8. Of the 25 patients with collagen disease, 23 had titers of 0, and two had titers of 4 and 6, respectively. Additional studies of those patients indicated that infection with Toxocara can be distinguished serologically from ascariasis, filariasis, and trichinellosis.