There are several groups of amoebae that are natural aquatic or soil organisms but are also opportunistic pathogens; that is, infection is coincidental to their normal life cycle.
The waterborne disease primary amoebic meningoencephalitis (PAM, sometimes called amoebic meningitis) was discovered at the Adelaide Children's Hospital in the 1960s. While it is a rare disease, there have been more than 20 fatal cases in Australia. It has since been reported from about 15 other countries in Africa, Asia, Europe and North and South America.
PAM is caused by Naegleria fowleri, and follows intranasal infection during swimming in warm, contaminated freshwater. Most victims have been children and the disease is almost invariably fatal. Infections have been linked with warm waters such as above-ground pipelines, tropical lakes, geothermal water, heated swimming pools or discharges of industrial cooling water. Until infections were identified in the USA in 2002, Australia was the only country where Naegleria fowleri had been associated with public water supplies.
Temperatures favourable for N. fowleri growth (grows fastest at 42˚C) occur in water piped above ground and in other man-made environments. N. fowleri exists in various forms including a dormant cyst which survives low temperature. These cysts have poor resistance to desiccation, so that this species rarely occurs in soil.
Control of Naegleria fowleri: Chlorine kills all life-cycle stages of Naegleria fowleri and is the most effective way to disinfect swimming pools. However, in rural water supplies chlorine does not always reach areas that the amoebae may colonise.
Acanthamoeba is a group of amoebae unrelated to Naegleria, but also free-living.
Ecology of Acanthamoeba: Acanthamoeba occur in freshwater, soil and marine environments.
The dormant stage (cyst) is highly resistant to desiccation in most species, making Acanthamoeba the most common protozoa in soil.
A fact sheet provides further infomation on sample requirements Pathogenic Free Living Fact Sheet