An ex vivo model of Toxoplasma recrudescence reveals the developmental plasticity of the bradyzoite stage

Reactivation of toxoplasmosis poses a significant health risk to chronically infected people especially those with compromised immune systems. Molecular studies of reactivation have been difficult due to the lack of accurate models of bradyzoite recrudescence, which initiates disease reactivation. Here, we performed single cell RNA-sequencing (scRNA-seq) on parasite populations that form after bradyzoite infection of two host-cell types: primary mouse astrocytes and human foreskin fibroblasts. The study revealed that metabolic gene signatures characterized distinct parasite populations and differences in the non-adapted bradyzoite population which uncovered significant developmental pluripotency. Our data revealed previously unknown complexity in the clinically important stages that form during reactivation of the bradyzoite tissue cyst. We sequenced >45,000 parasites at 1 billion reads per sample: recrudescent populations from infected mouse astrocytes at Day-2 (6,382), Day-5 (6,542), and Day-7 (26,931) post-bradyzoite infection; recrudescent populations from infected human fibroblasts at Day-2 (844), Day-5 (4,827), and Day-7 (1,206) post-bradyzoite infection.