Naegleria and Primary Amebic Meningoencephalitis
Minnesota Department of Health
Download a print version of this document:
Naegleria fowleri and Amebic Meningoencephalitis Fact Sheet (PDF)
What is Naegleria fowleri and Primary Amebic Meningoencephalitis?
Naegleria (nigh-GLEER-E-uh) is an ameba commonly found in warm freshwater and soil. Only one species of Naegleria infects people, Naegleria fowleri. It causes a very rare but severe brain infection called Primary Amebic Meningoencephalitis (PAM), which is often fatal.
How does someone become infected?
Naegleria fowleri infects people by entering the body through the nose. The ameba travels up the nose to the brain where it destroys the brain tissue. Generally, this happens when people go swimming or diving in warm freshwater, such as lakes or rivers.
More rarely, infections have been reported when people flush their sinuses with tap water contaminated with Naegleria fowleri. You cannot be infected by drinking contaminated water or swimming in a properly cleaned, maintained, and disinfected swimming pool. PAM cannot be spread from person-to-person.
What are the symptoms?
Symptoms of PAM usually start about 5 days after infection. Symptoms can be mild at first, but worsen very quickly. In its early stages, symptoms may include:
Later symptoms may include:
- stiff neck
- lack of attention to people and surroundings
- loss of balance
After symtpoms begin, the disease can move quickly and cause death within about 5 days.
People should seek medical care immediately whenever they have a sudden fever, headache, stiff neck, and vomiting - particularly if they have been in warm fresh water within the previous 2 weeks.
Where and when is it most common?
Naegleria fowleri is found all around the world, often in warm or hot freshwater (lakes, rivers, and hot springs). It is commonly found in lakes in southern-tier states, but has caused infections in more northern states, including Minnesota. The ameba grows best in warm or hot water.
While infections with Naegleria fowleri are rare, they occur mainly during the summer months of July, August, and September. Infections usually occur when it is hot for prolonged periods of time, which results in higher water temperatures and lower water levels. Infections can increase during heat wave years. It grows best at higher temperatures (up to 115°F) and when it is hot for extended periods of time. It can survive for short periods of time at higher temperatures. It is less likely to be found in the water as temperatures decline.
How do I know if a lake has this ameba?
Unfortunately, there is no rapid, standardized test to detect Naegleria fowleri in water. Recreational water users should assume that Naegleria fowleri is present in warm freshwater and that there will always be a low level risk of infection when entering these waters. Limiting the amount of water that goes up your nose and following the prevention suggestions will help reduce your risk.
How do you prevent it?
Naegleria fowleri is found in many freshwater lakes and rivers in the United States, and it is likely that a low risk of PAM will always exist with recreational use of freshwater lakes and rivers. The low number of infections makes it hard to know why some people have been infected compared to millions of other people using the same or similar waters across the U.S.
The only sure way to prevent PAM is to avoid participation in freshwater-related activities. You can reduce the risk of PAM by limiting the amount of water going up the nose. When taking part in water-related activities in bodies of warm freshwater:
- Avoid putting your head under the water
- Hold your nose shut or use nose clips
- Avoid warm freshwater when the water temperature is high and the water level is low
- Avoid digging or stirring up the sediment in shallow, warm freshwater areas
While rare, infections have happened using heated contaminated tap water for cleansing during religious practices or flushing sinuses (nose). If you are making a solution for flushing your sinuses here are some simple things you can do to avoid it:
- Boil water for 1 minute and let cool.
- Filter water using a filter designed to remove water-loving germs. The absolute pore size should be 1 micron or smaller.
- Buy and use only water that is labeled as distilled or sterile.