Naegleria fowleri: The Brain-Eating Amoeba
Naegleria fowleri, commonly referred to as the "Brain-Eating Amoeba," is a rare but deadly microorganism found in warm freshwater environments worldwide. While infections are extremely rare, they are often fatal, making understanding and mitigating the risks associated with this amoeba crucial.
Understanding Naegleria fowleri
Naegleria fowleri belongs to a group of amoebae called free-living amoebae. It is predominantly found in warm freshwater environments worldwide, including lakes, rivers, hot springs, and even poorly maintained swimming pools where warm temperatures and stagnant water create ideal conditions for its growth [1].
Naegleria fowleri begins as a cyst, a dormant form resistant to harsh environmental conditions. When conditions become favorable—typically in warm water above 25°C (77°F)—the cyst transforms into a feeding form known as a trophozoite. This trophozoite is the active form capable of infecting humans [2].
Infection and Symptoms
When contaminated water is forcefully inhaled, commonly during swimming or diving, the amoeba enters the body through the nose. Once inside the nasal cavity, the amoeba then travels along the olfactory nerve fibers to reach the brain. The entry of Naegleria fowleri into the brain triggers a severe and rapidly progressing infection known as primary amebic meningoencephalitis (PAM). The initial symptoms of PAM often resemble those of bacterial meningitis, including headache, fever, nausea, and vomiting. As the infection advances, neurological symptoms intensify, leading to confusion, seizures, and coma within a matter of days. The fatality rate of PAM is very high, with only a handful of documented survivors globally. Most people with PAM die within 1-18 days after symptoms begin [1].
Causes of Infection
Warm Freshwater
The amoeba thrives in temperatures typically above 25°C (77°F). Warmer climates and hot summer months create ideal conditions for its growth. Naturally hot water sources such as hot springs can also harbor Naegleria fowleri. The higher temperatures in these environments support its survival and growth [3].
Improperly Maintained Water Facilities
Swimming pools, splash pads, surf parks, and other recreational water venues that are poorly maintained or inadequately chlorinated can become breeding grounds for Naegleria fowleri. Stagnant or warm water with low chlorine levels can allow the amoeba to thrive and pose a risk to swimmers [3].
Tap Water
While less common, Naegleria fowleri has been found in tap water systems, particularly in warm water discharge areas from industrial or power plants. Water heaters can also support the growth of the amoeba if not properly maintained. Although ingesting water contaminated with Naegleria fowleri does not lead to infection, using untreated tap water in nasal devices, such as neti pots, is dangerous. For example, a person in southwest Florida died after rinsing their sinuses with tap water in 2023 [4].
Risk Factors
Naegleria fowleri infection is extremely rare, with typically fewer than 10 cases reported annually in the United States. However, the infection is almost always fatal, making it important to take precautions when swimming in freshwater [3].
In the United States, most cases of PAM caused by Naegleria fowleri have disproportionately affected young boys. The reasons behind this demographic trend remain unclear, but it is hypothesized that behaviors such as diving into water or playing in sediment at the bottom of lakes and rivers may increase the likelihood of exposure to the amoeba [3].
Traditionally, Naegleria fowleri infections have been concentrated in southern states of the United States where warm temperatures prevail for much of the year. States like Texas, Florida, and Louisiana historically reported more cases due to their conducive climates and abundance of freshwater bodies. However, since around 2010, there has been a noticeable shift in the geographical distribution of infections. Cases have been confirmed in states not traditionally associated with Naegleria fowleri, including Nebraska, Iowa, Minnesota, Indiana, Maryland, and even northern California [3].
Climate change is increasingly recognized as a contributing factor to this evolving distribution. Rising air temperatures globally lead to warmer water temperatures in lakes, ponds, and rivers, creating more favorable conditions for Naegleria fowleri to thrive. These environmental changes highlight the need for adaptive public health strategies that can effectively monitor and respond to emerging risks associated with Naegleria fowleri infections [3].
Prevention
To reduce the risk of Naegleria fowleri infection during water activities, consider the following precautions [5]:
Avoiding Warm Months: Naegleria fowleri thrives in warm freshwater environments, especially during hot summer months when water temperatures rise and water levels decrease. Minimize water-related activities during these periods to reduce exposure.
Nose Protection: When participating in activities like jumping or diving into water, hold your nose shut using your fingers or wear a nose clip. This prevents contaminated water from entering the nasal passages.
Head Above Water in Hot Springs: Hot springs and other geothermal water sources may harbor Naegleria fowleri due to their warm temperatures. Always keep your head above water to avoid inhaling potentially contaminated water.
Avoid Disturbing Sediment: Naegleria fowleri is more likely to reside in sediment at the bottom of shallow, warm freshwater bodies like lakes, ponds, and rivers. Avoid activities that involve digging into or stirring up sediment to minimize the risk of exposure.
Furthermore, Naegleria fowleri infections can occur when individuals use tap or faucet water for sinus or nasal rinsing, such as with neti pots or other nasal irrigation devices. When rinsing your sinuses or nasal passages, take precautions to ensure the water you use is safe [6]:
Boil Tap Water: Boiling water from the tap or faucet is an effective way to kill potential pathogens, including Naegleria fowleri. Boil the water for at least one minute, then allow it to cool to a safe temperature before using it for sinus rinsing.
Use Distilled or Sterile Water: Another safe option is to use water labeled as "distilled" or "sterile," which you can purchase at stores. These types of water are free from impurities and pathogens, ensuring they are safe for nasal irrigation.
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