Constitutive upregulation of transcription factors underlies permissive bradyzoite differentiation in a natural isolate of <i>Toxoplasma gondii</i>

<i>Toxoplasma gondii</i> is a widespread protozoan that chronically infects ~30% of the world's population. <i>T. gondii</i> can differentiate between the fast-growing life stage that causes acute infection and the slow-growing stage that persists in the host for extended periods of time. The slow-growing stage cannot be eliminated by the host immune response or currently known antiparasitic drugs. Studies on the slow-growing stage have been limited due to the limitations of <i>in vivo</i> experiments and the challenges of <i>in vitro</i> manipulation. Here, we characterize a natural isolate of <i>T. gondii</i>, which constitutively expresses factors that drive development and that is permissive to convert to the slow-growing stage under stress conditions <i>in vitro</i>. The strain presents a novel <i>in vitro</i> model for studying the chronic phase of toxoplasmosis and identifying new therapeutic treatments for chronic infections.