The “brain-eating amoeba,” Naegleria fowleri, is a microscopic organism that lives in warm freshwater environments. Though widely known for its severe consequences, infections with this amoeba are extremely rare. Understanding where this organism thrives, how it causes illness, and simple preventive measures can help individuals reduce their already low risk of exposure.
Understanding Naegleria Fowleri
Naegleria fowleri is a single-celled organism classified as an amoeboflagellate. This free-living microorganism primarily consumes bacteria in its natural environment. It exists in three forms during its life cycle: a dormant cyst, an active trophozoite, and a temporary flagellate stage.
The trophozoite is the infective stage. The flagellate form, characterized by two whip-like tails, can develop temporarily if there are changes in the water’s ionic strength. If water containing the trophozoite enters the human nose, the amoeba can migrate along the olfactory nerve to the brain. Once in the brain, it can cause severe tissue damage by consuming brain cells.
Environments Where the Amoeba Thrives
Naegleria fowleri is typically found globally in warm, still, or slow-moving freshwater. This includes lakes, ponds, and rivers. Hot springs are also common habitats for the amoeba.
The organism thrives in temperatures ranging from approximately 25°C to 46°C (77°F to 115°F). It often resides in the sediment at the bottom of these water bodies, where it finds ample food sources. While primarily associated with natural freshwater, Naegleria fowleri can also be present in poorly maintained or inadequately chlorinated swimming pools, splash pads, and even tap water if it is untreated or unfiltered. The amoeba cannot survive in saltwater or in water that is properly cleaned, cooled, and disinfected with adequate chlorine levels.
How Infections Occur and Their Rarity
Infection with Naegleria fowleri occurs almost exclusively when water containing the amoeba is forced up the nose. This typically happens during activities like swimming, diving, or engaging in water sports in affected freshwater environments. Swallowing water contaminated with Naegleria fowleri does not lead to infection.
Once the amoeba enters the nasal passages and travels to the brain, it causes a severe and rapidly progressing brain infection known as Primary Amebic Meningoencephalitis (PAM). This condition is nearly always fatal, with a mortality rate of 97% and 98%. Despite the severity of PAM, infections are extremely rare, with fewer than 10 cases reported annually in the United States. For instance, between 2013 and 2022, only 29 infections were reported in the U.S.
Preventive Measures for Water Activities
To minimize the already low risk of Naegleria fowleri infection, individuals can take several precautionary steps during water activities. Avoid swimming or diving in warm, still freshwater during periods of high temperatures and low water levels, as these conditions are more conducive to the amoeba’s growth. When participating in water activities in freshwater, holding the nose shut or using nose clips can help prevent water from entering the nasal passages.
Avoiding the stirring up of sediment in shallow freshwater areas, as Naegleria fowleri is more likely to reside in these bottom sediments. For those using hot springs, keep your head above the water. Swimming in properly maintained and chlorinated swimming pools significantly reduces the risk, as the amoeba cannot survive in adequately disinfected water. If using neti pots or other nasal rinsing devices, use distilled, sterile, or previously boiled and cooled tap water.