ANTIBODY RESPONSES TO TOXOCARA CANIS USING SERA FROM PARASITE‐INFECTED MICE AND PROTECTION FROM TOXOCARIASIS BY IMMUNISATION WITH ES ANTIGENS

Evidence for serological cross-reactions between Toxocara canis and related nematode parasites has been sought using sera from infected mice and the immunodiagnostic excretory/secretory (ES) antigen of T. canis larvae. Sera from mice experimentally infected with either T. canis, T. cati, T. pteropodis, Toxascaris leonina or Ascaris suum were tested for the presence of antibodies to T. canis ES antigen by solid-phase radioimmunoassay (RIA) or enzyme-linked immunosorbent assay (ELISA) using anti-mouse IgG. T. canis ES antigen was obtained from the medium used to culture T. canis larvae, this being the same source of antigen as has been used in a highly satisfactory immunodiagnostic test for human toxocariasis (visceral larva migrans). Sera from mice infected with either A. suum, T. cati or T. pteropodis showed definite cross-reactions with T. canis ES antigen in one or other of the two essays used. No reaction between anti-T. leonina sera and T. canis ES antigen was demonstrated, although infection levels with this parasite were low in mice. Concerning biological activity of ES antigen, it is of some interest that mice hyperimmunised with T. canis ES antigen in adjuvant were shown to be significantly resistant to infection by T. canis.