Naegleria fowleri
What is Naegleria?
Naegleria is a free-living single-celled organism called an amoeba. It can be found naturally in untreated fresh water and soil. Naegleria prefers temperatures between 25oC and 40oC and can grow in warm, stagnant water bodies such as lakes and hot springs. It can also occur in untreated water piped long distances above ground and in other man-made environments such as unchlorinated drinking water supplies and poorly maintained swimming pools, splash pads, wading pools and spas.
There are several species of Naegleria, but Naegleria fowleri is the only species that has been shown to cause disease in humans. It causes a very rare infection of the brain and brain coverings called primary amoebic meningoencephalitis (PAM). Even with treatment, most people with N. fowleri infection die.
How do you get infected with Naegleria fowleri?
Infection with N. fowleri can occur if water containing the amoebae is pushed up the nose. The amoebae travel up the nose to the brain where they infect and destroy brain tissue.
Infection may occur through activities such as jumping, diving or falling into water containing the amoebae. Infection can also occur following use of water with Naegleria for nasal irrigation or following domestic bathing and water play, for example when a young child falls or slips in bath water containing Naegleria, or when the water is forced up the nose during play with hose pipes, sprinklers and water toys.
Children and young adults appear to be more susceptible to infection than adults, although it can occur at any age.
The disease cannot be contracted by drinking water or through person-to-person contact. N. fowleri is not found in salt water.
Where in the environment can Naegleria occur?
Naegleria can potentially occur in any body of warm fresh water. This can include:
- lakes and rivers
- naturally hot water such as hot springs
- poorly maintained and under-chlorinated or unchlorinated swimming pools, wading pools and spas
- warm water discharge from industrial plants.
N. fowleri is found around the world. It grows best in warm water, especially between 25oC and 40oC, and any water body that seasonally exceeds 30oC or continually exceeds 25oC can support its growth
Naegleria can also be found in soil, however water is the only known source of human infection.
Can Naegleria be found in drinking water supplies?
Naegleria has been found in drinking water supplies that are not chlorinated or where the addition of chlorine is not well managed. They are most likely to enter the supply system at the source or at breaks in the sealed system such as open reservoirs or tanks. They can readily colonise biofilm that forms on the internal surfaces of pipes and tanks. Biofilm can dislodge from the surface and move to other parts of the water distribution system.
What about private bores?
N. fowleri has been identified where bore water is stored in above-ground dams and then piped over distances in above-ground pipes to private homes. The presence of N. fowleri will vary with ambient temperature, the distance water is piped, and the length of time the water is at favourable temperatures for amoeba growth and survival.
Does chlorine control Naegleria?
N. fowleri cannot survive in water that is clean, cool and chlorinated. Free chlorine or chloramines at 0.5mg/L or higher concentrations will control N. fowleri, provided that the disinfectant persists through the water supply system to the point of use.
Is there a simple and quick test for Naegleria in water?
No. Recognition of N. fowleri in water requires specialised testing. It should be assumed that any warm freshwater body as described above could contain N. fowleri.
How common are Naegleria infections?
Although N. fowleri can be commonly found in the environment, infection is rare. Cases of Naegleria meningoencephalitis have been recorded in South Australia, Western Australia, Queensland and New South Wales, and in many countries throughout the world.
In Australia, there have been five confirmed cases, and one probable case documented in Queensland since the year 2000. There have been three recorded cases in Western Australia, but none since 1985, and no cases in South Australia since 1981. . All Australian cases have been fatal. In the USA, between 1962 and 2024, there were 167 reported cases, of which only four survived.
How can I reduce the risk of infection with Naegleria?
To prevent infection:
- avoid jumping or diving into bodies of warm fresh water or thermal pools
- keep your head above water in spas, thermal pools and warm freshwater bodies
- empty and clean small collapsible wading pools and let them dry in the sun after each use
- ensure swimming pools and spas are adequately chlorinated and well maintained
- flush stagnant water from hoses before allowing children to play with hoses or sprinklers
- if the water supplied to your property is unchlorinated:
- don't allow water to go up your nose when bathing, showering or washing your face
- supervise children when bathing, showering and washing their faces to prevent water from going up their noses
- do not allow children to play unsupervised with hoses or sprinklers and teach them not to squirt water up their nose
- do not put your head under water when bathing or swimming in pools filled with untreated water
- avoid slip-n-slides and other activities where is it difficult to prevent water from going up the nose
- Water that may have N. fowleri should not be used for any form of nasal irrigation or nasal lavage including Neti (an Ayurvedic practice of nasal cleansing).
References and Related Content
Heymann, D., ed. 2008. Control of Communicable Diseases Manual, 19th edition. Washington, DC: American Public Health Association.
The Centers for Disease Control. Fact sheet on Naegleria infection
The Centers for Disease Control. Primary Amebic Meningoencephalitis – Arizona, Florida, and Texas, 2007. Morbidity and Mortality Weekly Report 2008;57:573-577
The National Health and Medical Research Council. Australian Drinking Water Guidelines (20110