<s>[INST] context: option-1-Naegleria fowleri: 1. Acute and fulminating primary amoebic meningoencephalitis (PAM) is caused by Naegleria fowleri. 2. Clinical features of N. fowleri: typical feature of meningitis with rhinitis are seen .The key to diagnosis is clinical suspicion based on recent history of swimming or diving in warm waters. NAEGLERIA FOWLERI ACANTHAMOEBA BALAMUTHIA Causes PAM(primary amoebic meningoencephalitis) Infective form -amoeboid form * Resides in fresh water pond * History of swimming in fresh water pond Flagellated forms-enter nares-cribriform plate-brain-PAM * So called "brain eating amoeba" Causes encephalitis-contact lens keratitis -optic route-Granulomatous encephalitis Aerosol route- lungs- brain - granulomatous encephalitis Causes granulomatous encephalitis option-2- Acanthamoeba species have been isolated as etiologic agents in Acanthamoeba keratitis: A. castellanii, A. polyphaga,. option-3- Disease: Granulomatous amebic encephalitis and Ulcerative keratitis option-4-E. histolytica and Entamoeba coli do not cause meningoencephalitis. [/INST] question: A 30yr old patient presented with features of acute meningoencephalitis in the casualty. His CSF on wet mount microscopy revealed motile unicellular microorganism. The most likely organism is - | options: A: Naegleria fowleri B: Acanthamoeba castellani C: E. histolytica D: Ent. Coli | answer: A </s>