Thursday, August 09, 2012
Q & A on Lily Lake Parasite
Health officials investigate death due to suspected amebic infection
The Minnesota Department of Health is investigating the death of an elementary school aged child due to suspected primary amebic meningoencephalitis (PAM), a very rare form of meningitis caused by an amoeba associated with warm freshwater. Confirmation will be made with the assistance of the Centers for Disease Control and Prevention.
The organism is known as Naegleria fowleri, an amoeba commonly found in warm freshwater and soil. It causes a very rare but severe brain infection and is nearly always fatal. The organism infects people by entering the body through the nose. Generally, this occurs when people use warm freshwater for activities such as swimming and diving.
Infections are very rare, even though Naegleria is commonly found in freshwater all over the world. While it can occur anywhere, infection with Naegleria usually occurs in warm southern states in the United States. Forty cases were reported in the United States from 2001 through 2011. The only previously confirmed case of this infection in Minnesota was reported in August of 2010.
Health officials acknowledged that the child had gone swimming at multiple locations in Washington County in the 2 weeks prior to illness onset, including Lily Lake in Stillwater. The previous Minnesota case’s likely source of infection was Lily Lake; Lily Lake has been closed to swimming until further notice.
“The risk of infection from Naegleria in Minnesota is very low," said Richard Danila, Assistant State Epidemiologist. “Swimming is a very healthy summertime activity and we do not want to discourage people from swimming. Rather, simply avoid swimming, diving or other activities in obviously stagnant water when temperatures are high and water levels are low,” Danila said.
Some additional precautions you can take while swimming during extremely warm periods include keeping your head out of the water, using nose clips or holding the nose shut, and avoid stirring up sediment at the bottom of shallow freshwater areas.
MDH-For more information, contact:
Assistant State Epidemiologist
Minnesota Department of Health
Naegleria and Amebic Meningoencephalitis
What is Naegleria?
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. Most infections are fatal.
How does infection with Naegleria occur?
Naegleria infects people by entering the body through the nose. Generally, this occurs when people use warm freshwater for activities like swimming or diving. The ameba travels up the nose to the brain and spinal cord where it destroys the brain tissue. Infections do not occur as a result of drinking contaminated water.
Where is Naegleria found?
Naegleria fowleri is found around the world. In the United States, it has caused infections in 16 states including MN. The ameba grows best in warm or hot water. Most commonly, the ameba may be found in:
- Bodies of warm freshwater, such as lakes, rivers
- Geothermal (naturally hot) water such as hot springs
- Geothermal (naturally hot) drinking water sources
- Warm water discharge from industrial plants
- Poorly maintained and minimally-chlorinated or unchlorinated swimming pools
- Naegleria is not found in salt water locations like the ocean.
Can I get Naegleria infection from a disinfected swimming pool?
No. You cannot get a Naegleria infection from a properly cleaned, maintained, and disinfected swimming pool.
How common are Naegleria infections in the United States?
Infections are very rare even though Naegleria is commonly found in freshwater. In the 10 years from 1998 to 2007, 33 infections were reported in the U.S. Thirty-one people had contact with recreational water and two people had contact with water from a geothermal (naturally hot) water supply.
When do Naegleria infections most commonly occur?
While infections with Naegleria are very rare, they occur mainly during the summer months of July, August, and September. These infections are more likely to occur in southern tier states. They usually occur when it is hot for prolonged periods causing higher water temperatures and lower water levels. Infections can increase during heat wave years.
Can infection be spread from one person to another?
No. Naegleria infection cannot be spread from one person to another.
What are the symptoms of Naegleria infection?
Infection with Naegleria causes the disease amebic meningoencephalitis also known as primary amebic meningoencephalitis (PAM), a brain infection that leads to the destruction of brain tissue. In its early stages, Naegleria infection may be similar to bacterial meningitis.
Initial symptoms of PAM start 1 to 14 days after infection. The initial symptoms include headache, fever, nausea, vomiting, and stiff neck. Later symptoms include confusion, lack of attention to people and surroundings, loss of balance, seizures, and hallucinations. After the start of symptoms, the disease progresses rapidly and usually causes death within 3 to 7 days.
Is there effective treatment for infection with Naegleria?
It is not clear. Several drugs are effective against Naegleria in the laboratory. However, their effectiveness is unclear since almost all infections have been fatal even when people were treated.
What should I do if I have been swimming or playing in freshwater and now think I have symptoms associated with Naegleria?
Infection with Naegleria is very rare. The early symptoms of Naegleria infection are more likely to be caused by other more common illnesses, such as meningitis. People should seek medical care immediately whenever they develop a sudden onset of fever, headache, stiff neck, and vomiting particularly if they have been in warm fresh water within the previous 2 weeks.
How common is Naegleria in the environment?
Naegleria is commonly found in warm lakes during the summer. This means that recreational water users should be aware that there will always be a low level risk of infection when entering these waters.
Is there a routine and rapid test for Naegleria in the water?
No. It can take weeks to grow and identify the ameba. Newer genetic detection tests for ameba are still under development. Water testing suggests that the amebae are so common that recreational water users should assume that there is a low level of risk when entering warm fresh water.
How does the risk of Naegleria fowleri infection compare with other water-related risks?
Although the infections are severe, the risk of Naegleria fowleri infection is very low. There have been 33 reported infections in the U.S. during the 10 years from 1998 to 2007, despite millions of recreational water exposures each year. By comparison, during the ten years from 1996 to 2005, there were over 36,000 drowning deaths in the U.S.
How will the public know if a lake or other water body has Naegleria?
Recreational water users should assume that there is always a low level of risk whenever they enter warm freshwater (for example swimming, waterskiing). Posting signs is unlikely to be an effective way to prevent infections. This is because the location and number of amebae in the water can vary a lot over time. In addition, posted signs might create a misconception that bodies of water without signs are Naegleria-free. Information about the risks of Naegleria infection should be put into public health messages discussing general issues of water safety and risk.
How can I reduce the risk of infection with Naegleria?
Naegleria is found in many warm freshwater lakes and rivers in the United States. It is likely that a low risk of Naegleria infection will always exist with recreational use of warm freshwater lakes, rivers, and hot springs. The low number of infections makes it difficult to know why some people have been infected compared to the millions of other people using the same or similar waters across the U.S. The only known way to prevent Naegleria infections is to refrain from water-related activities. However, some measures that might reduce risk by limiting the chance of contaminated water going up the nose include:
Minnesota Department of Health Website
- Avoid water-related activities in bodies of warm freshwater, hot springs, and thermally-polluted water such as water around power plants.
- Avoid water-related activities in warm freshwater during periods of high water temperature and low water levels.
- Hold the nose shut or use nose clips when taking part in water-related activities in bodies of warm freshwater such as lakes, rivers, or hot springs.
- Avoid digging in or stirring up the sediment while taking part in water-related activities in shallow, warm freshwater areas.