Naegleria is a genus of protozoa. The genus was named after French zoologist Mathieu Naegler. Naegleria is a microscopic amoeba that can cause a very rare, but severe, infection of the brain. The amoeba is commonly found in warm freshwater (for example, lakes, rivers, and hot springs) and soil. Only one species of Naegleria infects humans: Naegleria fowleri. 
Naegleria fowleri infects people by entering the body through the nose. This typically occurs when people go swimming or diving in warm freshwater places, like lakes and rivers. In very rare instances, Naegleria infections may also occur when contaminated water from other sources (such as inadequately chlorinated swimming pool water or heated tap water < 47°C) enters the nose. Once the amoeba enters the brain, it causes a usually fatal infection called Primary Amoebic Meningoencephalitis (PAM).  Naegleria are also notable because some species change their form based on the chemistry of their surrounding, transitioning from a immobile cell to a flagellated cell.
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