Question
List four parasites causing lesions in the brain. Describe the life cycle of any one of them. (2+4)
Answer
Four parasites causing lesions in the brain:
- Taenia solium (larval cysticercus stage — neurocysticercosis).
- Toxoplasma gondii (toxoplasmic encephalitis, particularly in AIDS).
- Naegleria fowleri (Primary Amoebic Meningoencephalitis).
- Echinococcus granulosus (cerebral hydatid cyst, an uncommon site). (Plasmodium falciparum — cerebral malaria — and Acanthamoeba/Balamuthia — Granulomatous Amoebic Encephalitis — are other valid examples.)
Life cycle of Taenia solium and neurocysticercosis (detailed): Humans acquire neurocysticercosis by ingesting T. solium eggs (via faeco-oral contamination or autoinfection from an intestinal tapeworm carrier — distinct from ingesting the cysticercus in undercooked pork, which instead causes adult intestinal tapeworm infection/taeniasis, with humans as the definitive host for the adult worm in that scenario). Ingested eggs hatch in the small intestine, releasing oncospheres that penetrate the intestinal wall and disseminate haematogenously to tissues including the brain, developing into cysticerci — small, translucent, fluid-filled cysts containing a single invaginated scolex — over weeks to months. In the brain, cysticerci commonly localize to the cerebral parenchyma, ventricles, or subarachnoid space, producing an inflammatory response (particularly as the cyst degenerates) that manifests clinically as seizures, the most common presentation, along with headache, focal neurological deficits, or hydrocephalus (if a cyst obstructs CSF flow). Neuroimaging (CT/MRI) classically shows multiple ring-enhancing lesions, sometimes with a visible scolex, at various stages (vesicular, colloidal, granular-nodular, calcified) reflecting the natural evolution/degeneration of the cyst over time.