Primary amebic meningoencephalitis (PAM) and guidelines for prevention

Follow these safeguards to prevent infection when swimming in lakes, rivers

​The following "white paper" was prepared by LCRA's Water Resource Protection Department, September 2007 and revised August 2011

Primary amebic meningoencephalitis (PAM) is a rare and usually deadly disease caused by infection with the ameba (Naegleria fowleri). The pathogenic potential in a human host was first described in 1965; the first reported case of PAM in Texas occurred in 1972, according to the Texas Department of State Health Services.

Lake LBJ
In August 2007, a 12-year-old boy became ill with PAM after spending two previous weeks at a summer camp on Lake LBJ. He was admitted to a hospital on Aug. 10 and, after being diagnosed with PAM, died Aug. 15. A second case involved a 22-year-old Lubbock man who contracted PAM after a trip to Lake LBJ on the weekend of Aug. 24. He reportedly sustained a ruptured eardrum while wake boarding. He was admitted to a Lubbock hospital on Aug. 31 and died Sept. 4. Both cases were confirmed by the Department of State Health Services.

Naegleria fowleri
According to information provided by the Department of State Health Services, the ameba that causes the infection lives in soil and in freshwater ponds, lakes, rivers, poorly or nonchlorinated pools, discharge or holding basins, and hot springs throughout the world. Naegleria thrives in warm, stagnant bodies of fresh water when temperatures are above 80 degrees. Consequently, cases of the disease usually occur from June through September. When water temperatures are below 80 degrees, the ameba exists in a cyst form that is not capable of causing infection. Naegleria fowleri is unique in that it exists in two different forms – pseudopod and flagellated. Transformation of ameba into flagellates is a distinctive feature of Naegleria.

Although the ameba is commonly found in the environment, cases of PAM are very rare. In the past 30 years, only a few hundred cases have been reported worldwide. Twenty-four infections were documented in the United States between 1989 and 2000. There have been 35 cases of PAM in Texas since 1972, including 10 cases since 2000, all fatal. The last reported case in Texas was in August 2010 from Tarrant County in North Texas. One previous PAM case involving the Highland Lakes was reported in 1980, when a 23-year-old female died after water skiing on Lake Austin.

According to the Department of State Health Services, Naegleria is believed to enter the body through the nose and travel to the brain via the olfactory nerve. The disease is not spread from person to person. A diagnosis of PAM is based on the results of an examination of the fluid in the patient's spinal cord or through the post mortem examination of brain tissue.

Prevention information
While the likelihood of exposure to Naegleria is high, the risk of infection is low. Additionally, the Department of State Health Services states that there are things swimmers should know and can do to lower the risk of infection. 

  • Avoid swimming or jumping into bodies of warm fresh water.
  • Do not swim in areas posted as "no swimming."
  • Hold your nose or use nose plugs when jumping or diving into water.
  • Use earplugs, swim goggles, or masks if you tend to get ear or eye infections.
  • Wash open skin cuts and scrapes with clean water and soap.

LCRA current activities/programs
LCRA’s routine bimonthly water quality monitoring program currently samples approximately 70 sites. There are four chemical sites (Wirtz Dam, Granite Shoals, Kingsland and headwaters) and two field parameter sites (FM 2900 and FM 1431) on Lake LBJ and all are located in the main channel (not coves). E. coli is the bacteriological test run. While LCRA routinely tests for E. coli bacteria, amebae are not bacteria, and therefore relating bacteria levels to amebae presence or absence cannot be correlated. While it is possible to test for the presence of the Naegleria fowleri, the test requires up to two weeks culturing the organism (the flagellated form is required for identification), and the test is not quantitative (presences/absences only).

In addition to the routine sampling program, LCRA supports a host of volunteer monitors through the Colorado River Watch Network (CRWN). More than 200 locations are sampled on a regular basis by these monitors. All monitors report water temperature, and several are trained to report bacteria levels (E. coli). LCRA also maintains two autoprofiling buoys at lakes Travis and LBJ. These unattended monitors record vertical profiles (temperature, dissolved oxygen, pH and specific conductance) through the water column twice per day. LCRA issues a water quality index monthly as part of its role as a steward of the lower Colorado River. The index characterizes the general quality of the river, tributaries and Highland Lakes using ratings of excellent, good, fair and poor. The index is based on a list of parameters, including dissolved oxygen, E. coli bacteria, nutrients (nitrogen and phosphorus), temperature and total dissolved solids.

The water quality index is intended to give the public a snapshot of overall water quality conditions. But conditions can change quickly. High water quality index ratings do not preclude the existence of bacteria that may cause infections. Swimming in a river, lake or pond, rather than a disinfected swimming pool, carries some risk. The public needs to take precautions at all times, such as avoiding stagnant water and staying out of the water after rains.


Although the ameba that causes the disease is common, cases of PAM remain very rare. The Texas Department of State Health Services reported the most effective prevention efforts are focused on public education regarding personal precautions.

Testing for Naegleria fowleri will not necessarily provide the public with definitive information. Also, testing takes two weeks to get results, and there are no public health criteria established for what levels of amebae present are acceptable or unacceptable.

​Q&A: A Water Recreation Disease
Where is this ameba found?
It is found worldwide, most commonly, in:

  • Warm bodies of fresh water, such as lakes, rivers
  • Geothermal water such as hot springs
  • Warm water discharge from industrial plants
  • Minimally chlorinated swimming pools
  • Soil

How common is this infection?
Although the ameba is commonly found in the environment, infection occurs rarely. Only 23 infections were documented in the United States between 1995 and 2004, according to the Centers for Disease Control and Prevention.

How does infection occur?
Infection with Naegleria occurs when the ameba enters the body through the nose. Generally this occurs when people are participating in water-related activities such as swimming underwater, diving, or other water sports that result in water going up the nose. The ameba then travels to the brain and spinal cord where it destroys the brain tissue.

What are the signs and symptoms of Naegleria infection?
Infection with Naegleria causes the disease primary amebic meningoencephalitis (PAM), a brain inflammation, which leads to the destruction of brain tissue. Initial signs and symptoms of PAM start one to 14 days after infection and include headache, fever, nausea, vomiting and stiff neck. As the amebae cause more extensive destruction of brain tissue, this leads to confusion, lack of attention to people and surroundings, loss of balance, seizures and hallucinations. The disease progresses rapidly, and infection usually results in death within three to seven days.

Is there treatment for infection with Naegleria?
Several drugs are effective against Naegleria in the laboratory. However, although a variety of treatments have been used to treat infected persons, their effectiveness is unclear because most infections have still been fatal.

Can infection be spread from person to person?
No. PAM cannot be spread from person-to-person contact.

How can I prevent an infection?

  • Avoid swimming or jumping into bodies of warm freshwater, hot springs and thermally polluted water such as water around power plants.
  • Avoid swimming or jumping into freshwater during periods of high temperature and low water volume.
  • Hold the nose shut or use nose clips when jumping or diving into bodies of warm fresh water such as lakes, rivers or hot springs.
  • Avoid digging in or stirring up the sediment while swimming in shallow water areas.
  • Do not swim in areas posted as "no swimming."

Source: Centers for Disease Control and Prevention

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