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Cambridge University Science Magazine

Amoebae might sound like science fiction creations, but in fact they are common single-celled organisms, found in soil and water across the world. Most are completely harmless, though there are exceptions: apart from Naegleria fowleri, another amoeba called Entamoeba can cause severe diarrhoea, often with life-threatening complications. Even Naegleria fowleri isn’t a brain-gnawing horror all the time. It normally lives in fresh water, where – if it doesn’t encounter a human host – it either eats bacteria, or, if food is scarce and temperatures low, it enters a dormant phase, like animals hibernating over the winter.

Naegleria fowleriis named after one of the Australian doctors who first identified it. In the 1960s, Carter and Fowler examined brain tissue samples from patients who had apparently died of meningitis (an inflammation of the membranes surrounding the brain). Meningitis is usually caused by bacteria or viruses, so the doctors were surprised to find no trace of either. Instead, they observed large numbers of amoebae, particularly in the olfactory nerve and olfactory bulb, which link the nasal passages to the rest of the brain. Carter and Fowler concluded that the amoebae caused the inflammation and somehow infected the patients by migrating up the nose, along the olfactory nerve and into the brain.

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