brain tissue cysts in infected mice with rh-strain of toxoplasma gondii and evaluation of bag1 and sag1 genes expression.

background : toxoplasma gondii is an obligate intracellular parasite that infects humans at high preva-lence rates. the virulent rh strain of t. gondii is generally considered to have lost its cyst forming ca-pacity. this study performed to obtain tissue cysts in mice infected with tachyzoites of rh strain treated with sulfadiazine (sdz). it provides the opportunity to analyze the conversion of tachyzoite to bradyzoite stage of the rh strain, followed by stage-specific gene-expression analyzing. methods : two groups of swiss-webster and balb/c mice were infected subcutaneously with 10 4 tachyzoites of t. gondii , rh strain and given sdz (300 mg/l) with nahco3 (5 g -1 ) in drinking water from day1 to day 14 post infection (p.i). the infected mice were sacrificed on day 50 post infection. their brains were removed and the numbers of tissue cysts were microscopically counted. total rna was extracted from brains and cdna synthesis was carried out. finally, rt-pcr (reverse tran-scription pcr) was used to detect the expression of bradyzoite (bag 1 ) and tachyzoite (sag 1 ) specif-ic genes during tachyzoite / bradyzoite stage conversion. results: sixty five percent of all infected mice were survived. cysts were detectable in mice brain (45%) on day 50 p.i. also rt-pcr of the brain samples was positive for sag1 and bag1. conclusion: it seems that conversion of tachyzoites to bradyzoites in brain of mice undergoing sdz was not completed until 50 days after inoculation.