EVALUATION OF FISHER RAT INFECTION BY TWO GENETICALLY DIFFERENT STRAINS OF Toxoplasma gondii: ANTIBODY KINETICS, RE-ISOLATION IN MICE, AND POLYMERASE CHAIN REACTION

THESIS: A. V. da Silva submitted this thesis for his Doctorate in Tropical Diseases at Botucatu School of Medicine, São Paulo State University, UNESP, Botucatu, São Paulo, Brasil, 2003.

Advisor: Professor Hélio Langoni

ABSTRACT. Toxoplasmosis show similar symptoms in humans and rats; these can be used as models for the disease in humans. Seven groups of rats received oral administrations of 10⁵ (Group 1), 10⁴ (Group 2), and 10³ (Group 3) Toxoplasma gondii bradyzoits from the BTU-2 strain, highly pathogenic to mice; 10⁵ (Group 4), 10⁴ (Group 5), and 10³ (Group 6) T. gondii bradyzoits from the ME-49 strain, less pathogenic to mice; and sterile saline solution (Group 7 Control). The animals were observed during 84 days, with weekly blood collection for serum and submitted to serological tests by modified agglutination test (MAT) and immunofluorescent antibody test (IFAT) for IgG and IgM subtype antibodies. At the end of observation, the animals were killed and their tissue samples were obtained to re-isolate the parasite and detect T. gondii DNA by polymerase chain reaction (PCR), using specific oligonucleotids for detecting SAG-1, B1, rDNA, and non-coded repetitive sequences (REP). The BTU-2 strain was classified by the SAG-2 gene polymorphism. All rats developed detectable antibody titers, regardless of the strain used. The most frequent differences in serological results were in the Groups that received 10⁵ and 10³ bradyzoits, regardless of the strain used. The BTU-2 strain induced higher titers than ME-49 strain to IgM, IFAT, and MAT from the 35^th day of infection. The BTU-2 strain was also isolated from all brain and muscle samples, no matter the dosage used to infect the animals. When the ME-49 strain was used, the parasite was isolated more frequently in the brain than muscles, influenced by the infective dosage. The PCR-REP technique was the most effective in parasite detection, mainly in muscle samples, with T. gondii DNA in 75% of all studied samples. The BTU-2 strain was classified as type III by the SAG-2 gene polymorphism.

KEY WORDS: Toxoplasma gondii; serology; re-isolation; PCR; genotyping; rat.

CORRESPONDENCE TO: A. V. Silva – Rua Laurindo Izidoro Jaqueta, 225, Jardim Paraíso, 18610-240, Botucatu, São Paulo, Brasil. Phone: 55 14 3882 0240. E-mail: silva.av@uol.com.br