Genetic analysis of the diversity in Toxoplasma gondii.

More than 50 different genetic markers are now available for Toxoplasma gondii isolate typing. For most of them, allelic polymorphism is low (2 to 4 alleles). A few markers, more polymorphic, can be used to fingerprint isolates for epidemiological studies. Phylogenetic analysis detects 2 main groups in Toxoplasma population. Group 2 is genetically heterogeneous. From a practical point of view, 3 main types (types I, II and III) are usually considered. Multilocus genotyping is necessary to reveal atypical or recombinant genotypes, more frequent among isolates collected in remote areas or in wild game. Toxoplasma isolates from human toxoplasmosis are mainly from type II (whatever the severity of clinical disease), but type I and atypical genotypes are found only in severe cases of human toxoplasmosis.