Immunological comparison of 124 isolates of Toxoplasma gondii.

We tested 124 isolates of Toxoplasma gondii, as determined morphologically and by their ability to elicit antibodies in the dye test with the RH strain of Toxoplasma in mice. They were compared for their capacity to immunize CF-1 mice against isolate T-1, and T-1 immune mice for their capacity to resist each of the 123 other isolates. Of the 125 isolates, 52 had been isolated in the continental USA, 33 in Central America, 15 in Europe, 9 in Hawaii, five in Japan, two in Taiwan, five in Australia, one in Indonesia, one in Tunisia, and one was of unknown origin. Complete cross-immunity was found. This suggests that only one immunotype of Toxoplasma is prevalent in the United States, and perhaps all over the earth. Vaccines are likely to immunize against most or all Toxoplasma isolates.