Correlation between antibody levels in Toxoplasma gondii infected pigs and pathogenicity of the isolated parasite.

Sera and diaphragm muscle tissues were obtained from 109 commercial pigs between September 1991 and May 1992 from the slaughterhouse at La Plata, Provincia Buenos Aires, Argentina. Anti-Toxoplasma gondii IgG antibody reactivity to T. gondii antigens were assayed using sera by indirect immunofluorescence assay and immunoblotting technique. Anti-T. gondii IgG titers at serum dilutions of 1:1024 and higher were noted in 11.0% of the tested sera, and at dilutions of 1:16 and lower in 36.7% of the serum samples. Using mouse inoculation test, T. gondii was isolated from 14 pig diaphragm samples. Of five samples derived from pigs with antibodies at dilutions of 1:1024 and higher, four contained trophozoites which, when inoculated into mice intraperitoneally, killed all recipient hosts within 15 days post inoculation. Parasites detected in seven out of eight samples from pigs with antibodies at serum dilutions of 1:64 and lower formed cysts in the brain, and mice survived longer than 13 days post inoculation. Immunoblotting demonstrated antibody reactivity in pig sera samples with relatively high titers for parasite antigens. Results of the present study suggest that antibody production in infected pigs is apparently dependent on the pathogenicity of the parasite strain.