Antibody responses measured by various serologic tests in pigs orally inoculated with low numbers of Toxoplasma gondii oocysts.

OBJECTIVE

To follow antibody responses measured by various serologic tests in pigs orally inoculated with low (< or = 10 oocysts) numbers of Toxoplasma gondii oocysts.

ANIMALS

24, 2- to 3-month-old pigs.

PROCEDURE

Pigs (n = 42) were inoculated orally with 10 (14 pigs) or 1 (28 pigs) infective oocysts, and 6 pigs served as uninoculated controls. Blood (serum) samples were obtained at 1- to 3-week intervals until euthanasia. At necropsy, the brain, heart, and tongue of pigs were bioassayed in mice and cats for isolation of T gondii. Modified agglutination test (MAT), using whole, fixed tachyzoites and mercaptoethanol; latex agglutination test (LAT); indirect hemagglutination test (IHAT); Sabin-Feldman dye test (DT); and ELISA were used to evaluate serologic responses to T gondii.

RESULTS

T gondii was isolated from tissues of 13 of 14 pigs each fed 10 oocysts, 17 of 28 pigs each fed 1 oocyst, and 0 of 6 control pigs. 29 of 30 T gondii-infected pigs developed antibodies when measured by MAT, DT, and ELISA; the 1 seronegative-infected pig had been fed 10 oocysts and was euthanatized 69 days after inoculation. LAT detected antibodies in 26 of 30 T gondii-infected pigs. IHAT detected antibodies in 11 T gondii-infected pigs.

CONCLUSION

MAT, DT, and ELISA were more sensitive serologic assays than LAT and IHAT for detecting antibodies induced by low numbers of T gondii in pigs.