Brain under Parasitic Siege — A Comprehensive Descriptive Review of Neuroparasitic Diseases - Figure 2

Toxoplasma gondii is an intracellular protozoan (Figure 2) that invades the host via ingestion of cysts or oocysts. After systemic dissemination, tachyzoites (Figure 2) penetrate the blood–brain barrier through infected leukocytes and direct endothelial adhesion. Within the CNS, tachyzoites replicate in neurons and glial cells, forming parasitophorous vacuoles; immunological pressure induces conversion into bradyzoites with chronic cyst formation. In immunocompromised patients, latent bradyzoites reactivate, leading to focal necrotising encephalitis with marked microglial activation, perivascular lymphocytic infiltration, and cytokine‑mediated neuroinflammation that disrupts neural circuits and contributes to cerebral oedema (Elsheikha, Marra, & Zhu, 2020; Dubey & Jones, 2008).