8 months ago
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Primary amoebic meningoencephalitis (PAM) is caused most often by Naegleria fowleri, sometimes called the “brain-eating amoeba”. N. fowleri lives in warm freshwater, including lakes, hot springs, and in poorly chlorinated pools.
An infection begins when contaminated water rushes up the nasal passages. The amoeba travels along the olfactory nerves, passing through the cribriform plate and into the olfactory bulbs of the brain.
Unlike viruses, N. fowleri is a free-living amoeba. In nature it survives by feeding on bacteria. Once in the brain, however, it mistakes neurons and glial cells for food. It uses small projections called amoebostomes that literally bite into host cells, ingesting their contents piece by piece. It also releases enzymes and toxins in the form of proteases, phospholipases, and pore-forming proteins that dissolve tissue and kill the host cells.
So “brain-eating” isn’t just a metaphor: N. fowleri actively consumes living neural cells as a source of nutrients. And as the pathogen feeds and multiplies, its proliferation triggers a profound inflammatory response in the host’s body.
The immune system floods the brain with neutrophils and cytokines, causing swelling, bleeding, and necrosis. Together with the amoeba directly consuming the cells, the result is a rapid and catastrophic destruction of brain tissue. For added measure, PAM also progresses very rapidly, often going from the first symptoms to death in under 10 days.
This is also why an N. fowleri infection is far more lethal than viral encephalitis.
