The three life stages of Naegleria fowleri The amoeba almost always infects humans in the trophozoite stage (elongated structure shown at center), when it is actively feeding and multiplying. When environmental conditions become unfavorable, such as during winter, the amoeba develops flagella (threadlike appendages used for locomotion, attached to pear-shaped structures shown at bottom) and moves about in search of food. If unfavorable conditions continue, it loses its flagella and enters the metabolically inactive cyst stage (round structures shown in and near corners) and remains dormant until the return of favorable conditions. Some experts classify N. fowleri infection via water (containing trophozoites) as wet infection and that via sediment (containing cysts) as dry infection. (more) Naegleria fowleri A Deadly Brain-Eating Amoeba Ask the Chatbot a Question More Actions Share Share Share to social media Facebook X URL https://www.britannica.com/science/Naegleria-fowleri Feedback Corrections? Updates? Omissions? Let us know if you have suggestions to improve this article (requires login). Feedback Type Select a type (Required) Factual Correction Spelling/Grammar Correction Link Correction Additional Information Other Your Feedback Submit Feedback Thank you for your feedback Our editors will review what you’ve submitted and determine whether to revise the article.

　　External Websites Centers for Disease Control and Prevention - Naegleria Fowleri - Primary Amebic Meningoencephalitis (PAM) - Amebic Encephalitis Ask the Chatbot a Question Written by Written by Manjishtha Bhattacharyya Manjishtha Bhattacharyya is an editor at Encyclopaedia Britannica. She holds a PhD in zoology from Vidyasagar University, West Bengal, and has more than seven years of experience in science communication... Manjishtha Bhattacharyya Fact-checked by Fact-checked by The Editors of Encyclopaedia Britannica Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree.... The Editors of Encyclopaedia Britannica Last Updated: Oct. 8, 2025 •Article History Table of Contents Table of Contents Ask the Chatbot Naegleria fowleri is an amoeba (one of a group of single-celled microorganisms) found in warm, moist soil and bodies of warm fresh water around the world. It usually feeds on bacteria, but it targets human brain cells when it accidentally enters the body through the nose. The result is a rare but frequently fatal brain infection called primary amoebic meningoencephalitis (PAM). Taxonomy The three life stages of Naegleria fowleriThe amoeba almost always infects humans in...

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