A 25-year-old patient presented with signs of meningoencephalitis following swimming in a nearby local pond one week back. The CSF on wet mount microscopy revealed motile unicellular microorganisms. The most likely organism is

The given clinical scenario is suggestive of Primary amoebic meningoencephalitis caused by Naegleria fowleri. It is also known as Brain-eating amoeba. It occurs in 3 forms: cyst, amoeboid trophozoite and flagellate trophozoite forms. The infection usually follows swimming in the freshwater rivers or ponds. The amoebae invade the nasal mucosa and pass through the olfactory nerve branches in the cribriform plate into the meninges. Incubation period is 2 days to 2 weeks. Treatment: Intravenous Amphotericin B Reference: Paniker&;s Textbook of Medical Parasitology 8th edition