Experimental Toxoplasma gondii infection in raccoons (Procyon lotor)

Six raccoons (Procyon lotor) without detectable Toxoplasma gondii antibodies were used. Four raccoons were inoculated orally (2 with oocysts and 2 with tissue cysts) with ME49 strain of T. gondii and 2 raccoons were not inoculated with T. gondii. All raccoons remained clinically normal. Raccoons were killed between 59 and 61 days after inoculation and portions of their heart, skeletal muscle, and brain were digested in pepsin solution, and homogenates were bioassayed in mice. Toxoplasma gondii was isolated from all 4 inoculated raccoons; from the heart of 3, skeletal muscles of 2 and the brain of none. All 4 inoculated raccoons developed antibody titers > or = 1:1,600 in the modified direct agglutination test (MAT) using whole formalinized tachyzoites. Toxoplasma gondii antibody titers of the raccoons not inoculated with T. gondii remained < 1:25, and T. gondii was not isolated from their tissues. It was concluded that muscle tissue from multiple sites including the heart was the tissue of choice for conducting parasitologic surveys for T. gondii in raccoons. Evaluation of the sera of the experimentally infected raccoons in the Sabin-Feldman dye test, latex agglutination test, and the indirect hemagglutination tests indicated that the MAT detected antibodies faster and in higher titers than did the other serological tests.