Reports of the “brain-eating amoeba” can cause alarm, but infections are extremely rare. This microscopic organism, Naegleria fowleri, is naturally present in certain environments, yet human cases remain exceptionally uncommon. Understanding the specific circumstances helps put the risk into perspective.
The Amoeba Behind the Cases
Naegleria fowleri is a free-living amoeba that thrives in warm freshwater environments worldwide. Common habitats include lakes, rivers, hot springs, and poorly chlorinated swimming pools or water heaters.
When water containing Naegleria fowleri enters the nose, the amoeba can travel to the brain, causing primary amebic meningoencephalitis (PAM). PAM is a rapidly progressing infection of the central nervous system that destroys brain tissue. Naegleria fowleri is the only known species of Naegleria that causes this fatal human disease.
Tracking Brain-Eating Amoeba Cases
In the United States, fewer than 10 cases of primary amebic meningoencephalitis (PAM) are reported each year. From 1962 to 2021, 154 infections were documented in the U.S., with only four individuals surviving.
The geographic distribution of cases has shown some shifts. Historically, most U.S. cases occurred in southern states, such as Florida and Texas, particularly during warmer summer months. Recent data indicates a northward expansion, with cases reported in states like Minnesota, Indiana, and Missouri since 2010. This suggests the range of Naegleria fowleri exposures is broadening, potentially influenced by rising water temperatures.
How Infections Occur
Infections with Naegleria fowleri primarily happen when water containing the amoeba enters the nose. This occurs during recreational activities in warm freshwater, such as swimming, diving, or water skiing. The amoeba then travels from the nasal passages to the brain, leading to severe illness.
Naegleria fowleri infection cannot be acquired by swallowing contaminated water; it must enter through the nose. The infection also cannot spread from person to person. While most cases are linked to natural freshwater bodies, infections have occurred from using contaminated tap water for nasal rinsing, such as with a neti pot.
Protecting Yourself from Infection
Several steps can help reduce the risk of Naegleria fowleri infection. When engaging in water-related activities in warm freshwater, consider holding the nose shut, using nose clips, or keeping the head above water. Avoiding jumping or diving into warm freshwater, especially during peak summer months, can also lower exposure risk.
Avoid stirring up sediment at the bottom of shallow warm freshwater bodies, as the amoeba is more likely to reside there. For individuals who irrigate their sinuses, using distilled, sterile, or previously boiled and cooled water is crucial. These measures help minimize contact with Naegleria fowleri.