Biological function and genotype identification of the isolated Toxoplasma gondii strain from human peripheral blood

Toxoplasma gondii (T. gondii), an obligate intracellular protozoan, can infect humans and other warm-blooded animals, causing toxoplasmosis-a zoonotic parasitic disease with a global distribution. Although the isolation of T. gondii strains from animal tissues for genetic characterization is well established, isolation from clinical samples remains challenging due to the chronic infection features, such as tissue cysts and the absence of circulating parasites. Here, we isolated a novel T. gondii strain (designated TgHumanCs1) from human peripheral blood through a comprehensive approach combining serological (indirect hemagglutination assay), molecular (PCR), and biological assay (mouse bioassay). The strain exhibited an invasive and proliferation capacity comparable to the RH strain in vitro, as well as high virulence in murine models. Multilocus PCR-RFLP genotyping (targeting GRA6, Apico, SAG2, and SAG3) revealed that TgHumanCs1 displays a Type I allele pattern and clusters with the RH strain. The successful isolation of TgHumanCs1 underscores the potential for hematogenous dissemination of highly virulent T. gondii strains in human infections, and highlights the need for continued surveillance of circulating parasite genotypes in clinical settings.