Submitted to: Veterinary Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 13, 1996
Publication Date: N/A
Interpretive Summary: Infection by the protozoan parasite, Toxoplasma gondii causes mental retardation and loss of vision in children and abortion in livestock. Humans become infected with T. gondii by ingesting infected meat, by ingesting food and water contaminated with oocysts from infected cat feces, or congenitally. Infected pigs are considered as an important meat source of Toxoplasma for humans. Serologic examination is an effective way of diagnosis of toxoplasmosis in pigs. Scientists at the Beltsville Agricultural Research Center report antibody responses of pigs experimentally infected with T. gondii. They found that antibodies persisted in pigs for more than 2 years. The results will be of interest to public health workers, veterinarians and diagnosticians.
Antibody titers to Toxoplasma gondii were determined in 16 pigs orally inoculated with 1000 or 10000 oocysts of 1 of the 4 strains (GT-1, ME-49, TS-2 and TC-2) of T. gondii. Pigs were euthanized postinoculation day (PID) 103 to 875 and their tissues were bioassayed for T. Gondii. Antibody titers were measured in the modified agglutination test (MAT) using formalin-preserved (test A) or acetone-preserved (test B) tachyzoites, latex agglutination test (LAT), indirect hemagglutination test (IHA), enzyme linked immunobsorbant assay (ELISA), and the Sabin-Feldman dye test (DT). Toxoplasma gondii was isolated from all but 2 (1 with GT-1 strain and 1 with TC-2 strain) of the inoculated pigs. Results of the serologic tests varied by test used, by strain of T. gondii and from pig to pig within groups. One pig inoculated with the TC-2 strain was considered to be not infected because it remained seronegative in all tests and T. gondii iwas not isolated from its tissues by bioassay. The IHA and LAT did not produce consistently positive results with infected pigs and 2 pigs remained seronegative (greater than 1:64) in both tests. At the time of necropsy, IHA titers had declined to greater than 1.64 in 5 pigs and LAT titers had declined to greater than 1:64 in 4 pigs. The MAT (test A) and ELISA detected antibodies in all infected piigs but ELISA did not detect antibody at the time of necropsy in 1 pig. Antibody titers peaked earliest in the DT. Antibody titers in the MAT (test B) peaked at 2560 in all seropositive pigs by 6 weeks postinoculation but declined to greater than 1:160 by 15 weeks postinoculation; this test may be useful in determining recency of T. gondii infection in pigs. Overall, the MAT (test A) gave most consistant results.