Recognizing Symptoms of the Brain-Eating Amoeba

The first and most common symptom of Naegleria fowleri is a high fever. Usually, symptoms develop within five to seven days of exposure to warm freshwater.

In rare cases, however, signs of illness may appear within 24 hours or may not develop for up to 15 days. While many infections and conditions can cause a fever, this symptom becomes a red flag when paired with neurological signs.

While many of the early symptoms of Naegleria fowleri mimic common illnesses, this amoeba can cause a distinctive headache. People often describe it as intense and throbbing, unlike a standard tension headache.

It usually doesn’t respond to over-the-counter pain relievers and can feel like pressure behind the eyes or forehead. Some case reports liken the pain to a migraine—but “deeper” inside the head.

Stomach issues like nausea, vomiting, or general discomfort are extremely common symptoms across many illnesses. They are also early signs of Naegleria fowleri.

Because PAM is so rare, most people should first consider other causes for these symptoms—unless they also have a high fever or severe headache.

Case reports often note that nausea may be paired with fatigue or general weakness. Even if these symptoms stem from another illness, prompt medical care is still a good idea.

Neck stiffness is another signature early symptom of PAM. As the infection spreads, tissues in the head swell, making it painful or difficult to bend the neck.

Bright light may also become overwhelming and trigger eye pain—a symptom called photophobia. Stiff neck and light sensitivity are also seen in bacterial meningitis.

For the best possible outcome, early evaluation by a medical professional is essential.

The infection damages the brain, leading to disorientation, memory issues, and unresponsiveness. A person may forget where they are, struggle to speak, or act strangely.

These are signs of severe brain involvement. Naegleria fowleri can progress quickly from confusion to coma or death.

As brain damage and swelling continue, symptoms like loss of balance or sudden seizures can occur. If parts of the brain that control movement are affected, people may experience anything from minor clumsiness to full loss of leg function.

A sudden seizure may indicate severe neurological involvement and marks a critical turning point in disease progression that requires immediate intervention.

PAM progresses quickly. After symptoms begin, an infected person often enters a coma within a few days. On coma response scales, most patients fall into the “severe” range, indicating significant brain damage.

At this stage, survival is extremely rare. Death often occurs within a week to 10 days after symptoms start. However, some people have survived—typically after rapid diagnosis and aggressive treatment.

Though survival rates remain low, they’re improving as doctors learn more about Naegleria fowleri.

There is a lot of misinformation about how spreads. Despite common belief, a person cannot become infected by drinking contaminated water.

The amoeba must enter the body through the nose—usually while swimming, diving, or playing in warm freshwater. It then travels up the olfactory nerve to the brain.

Newer research shows that water must reach deep into the nasal cavity to carry the amoeba far enough.

PAM cases have also occurred after people used nasal rinsing tools like neti pots or bulb syringes. These devices are now estimated to be responsible for up to 9% of global cases.

Most Naegleria fowleri infections occur in warmer states like Texas and Florida. The amoeba thrives in hot freshwater environments, especially lakes and rivers.

With climate change, the range has expanded north—cases have even been documented as far as Minnesota.

Infections primarily affect children and young adults, especially in the summer when water temperatures are higher.

PAM is one of the rarest but most lethal infections known. Fewer than 10 U.S. cases are reported each year, even in high-risk regions.

Because water must enter the nose in a very specific way, the odds of infection remain low. But once Naegleria fowleri enters the brain, it can destroy healthy tissue in a matter of days.

This fast progression, along with symptoms that resemble meningitis, contributes to its 97% fatality rate. Some scientists believe mild cases may occur and resolve on their own—but these go undetected.

Anyone who develops these symptoms after freshwater exposure should seek emergency care immediately. It’s important to tell providers about recent water exposure to speed up diagnosis.

Because there’s no single test for PAM, any detail helps guide treatment. PAM treatment is aggressive and often involves cooling the body to reduce swelling.

Antifungal and antimicrobial medications may be given orally, intravenously, or directly to the brain. In recent years, doctors have begun using new compounds that show strong potential for killing Naegleria fowleri.