<s>[INST] context: Naegleria fowleri, the only pathogenic species of naegleria Human infection comes from water containing the amoebae and usually follows swimming or diving in ponds. Patients are mostly previously healthy young adults or children. The amoebae invade the nasal mucosa, pass through the olfactory nerve branches in the cribriform plate into the meninges and brain to initiate an acute purulent meningitis and encephalitis (primary amoebic meningoencephalitis). The incubation period is 2 days to 2 weeks. The disease almost always ends fatally within a week Diagnosis can be made by CSF examination. The fluid is cloudy to purulent, with prominent neutrophil leucocytosis, elevated proteins and low glucose, resembling pyogenic meningitis. Failure to find bacteria in such specimens should raise the possibility of PAM. Wet film examination of CSF may show the trophozoites. Cysts are never seen CSF or brain. At autopsy, trophozoites can be demonstrated in brain histologically.Culture can be obtained in agar seeded with Escherichia coli or in the usual cell cultures used for virus isolation. Both trophozoites and cysts occur in culture. Amphotericin B has been used in treatment with limited success TEXTBOOK OF MEDICAL PARASITOLOGY,CKJ PANIKER,6TH EDITION,PAGE NO 33 [/INST] question: A 30-yebar old patient presented with features of acute meningoencephalitis in the casualty. His CSF on wet mount microscopy revealed motile unicellular microorganisms. The most likely organism is - | options: A: Naegleria fowleri B: Acanthamoeba castellani C: Entamoeba hystolytica D: Trypanosoma cruzi | answer: A </s>