[Toxoplasma gondii--known and unknown parasite].

The protozoan Toxoplasma gondii, described by Nicolle and Manceaux in 1908, is a ubiquitous and cosmopolitan parasite that infects a wide range of mammal and bird species. Although the parasite possesses a meiotic lifecycle phase it represents very unusual population structure comprising three archetypal clonal lines: I, II and III, which together account for over 95% of strains isolated in Europe and North America. The isolates from South America are more genetically diverse. Molecular phylogeny studies and phenotype analyses showed recently 11 successful parasite lineages (haplogroups) of different global distribution. Individual T. gondii strains vary strongly in their virulence which is very well defined in mice: there are extremely virulent strains (of RH type) with LD100=1 and low virulent strains (LD50 > or = 1000), without any intermediate virulence strains. The article presents some recent data on the population structure and virulence of the parasite, mapping of virulence loci and new identified rhoptry antigens (ROP18 and ROP16) as major virulence components.