Naegleria fowleri, better known as “brain-eating amoeba”, is a free-living amoeba that is a major cause of a rare brain infection called Primary Amebic Meningoencephalitis, which typically affects young people with a history of swimming in warm fresh water such as a lake or stream. After entering the nose and crawling up the olfactory nerves into the frontal lobes, the amoebae rapidly destroy neural tissue. Microscopically, the trophozoites are often found along the leptomeninges and around cerebral blood vessels (depicted here). The organisms have a dark (hyperchromatic) central nucleus and many cytoplasmic vacuoles, a morphological appearance that superficially resembles macrophages on light microscopy. Before ingesting the brain tissue, the amoeba secretes digestive juices to break it down, giving the brain tissue a disrupted and partially dissolved appearance. Hemorrhagic infarction (stroke) is common. Death is usually rapid, often occurring within days to ~1 week after initial infection.
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