From Detection to Control: Enhanced Strategies for Managing Naegleria fowleri in Drinking Water Systems

The challenge

Maintaining water quality in Australian drinking water distribution systems (DWDS) is challenging, particularly in the rural areas in Western Australia. Factors such as long above-ground DWDS lead to elevated water temperatures, which in turn enhance biofilm formation and microbial activity. These conditions decrease water quality and contribute to the loss of disinfectant residuals (chlorine and monochloramine). Consequently, pathogenic amoeba, such as Naegleria fowleri, become a critical operational and public health concern.

Our response

Our project aimed to provides a better understanding of the physical, chemical and biological conditions that support N. fowleri’s presence and persistence, develop novel tools to identify and predict DWDS susceptibility to N. fowleri colonisation and establish validated management strategies for its elimination in DWDS. The project findings contribute to improving Naegleria monitoring and management by water utilities in Australia and worldwide.

The results

Our most significant contribution has been delivering improvements to Naegleria fowleri management in DWDS through better detection methods, a comprehensive understanding of factors supporting their presence and persistence and enhanced management methodologies. The outputs of the project have influenced water management and surveillance strategies both within Australia and internationally. Detailed highlights of our research are as follows.

• Better detection methods.

N. fowleri is the waterborne causative agent of the highly fatal disease primary amoebic meningoencephalitis (PAM), and rapid detection in water samples is paramount to maintaining a safe and secure water supply. We developed a rapid detection system specific for N. fowleri. The system reduced sample analysis time from several days to just hours, ensuring more timely and effective operational responses to N. fowleri detections.

• Seasonality and conditions supporting N. fowleri.

Using our new detection method, we identified the presence, concentration and persistence of N. fowleri in relation to physical, chemical and biological conditions within DWDS. Our work confirmed that chlorine concentrations had the greatest impact on N. fowleri presence, and distance from the chlorination location point was also significant. We also identified that N. fowleri can be seasonally present in both the bulk water and pipe-wall biofilm, though at different concentrations, with pipe-wall biofilm being the likely long-term reservoir for N. fowleri.

• Microbial ecology supporting N. fowleri colonisation.

We investigated the biological conditions, especially the microbial community ecology, in operational DWDS that support the presence of N. fowleri compared to other Naegleria species. We identified distinct microbial communities associated with different Naegleria species, even under similar physical and chemical conditions. A statistically significant association was found between N. fowleri presence and the microbial community composition supporting its growth. We subsequently characterised the bacterial species within N. fowleri, N. lovaniensis and other amoebae from different field sites and identified individual bacterial food sources preferred by N. fowleri. These bacterial species represent potential biomarkers for predicting N. fowleri colonisation, which could inform the next generation of proactive management strategies.

• Improved management protocols for N. fowleri

As the project identified that biofilm as the likely reservoir for N. fowleri in DWDS, we investigated limitations and defined optimal management strategies. Laboratory studies showed that intermittent disinfection with 0.6 mg/L free chlorine was not sufficient to remove all viable N. fowleri from biofilm. A trial with field biofilm samples demonstrated that shock disinfection with 0.5-10 mg/L free chlorine was also insufficient to eliminate viable N. fowleri. However, a field-based trial using an operational DWDS containing N. fowleri in pre-chlorinated water and biofilm demonstrated successful removal of N. fowleri from both bulk water and biofilm when a constant free chlorine concentration above 1 mg/L was maintained. This was the first study globally to confirm the disinfectant residual concentration required to eliminate N. fowleri from both bulk water and biofilm, as well as prevent recolonisation of N. fowleri.

Contact for further information: Geoffrey Puzon (geoffrey.puzon@csiro.au)

Photo:

Fluorescent microscopy photo of a Naelgeria. fowleri trophozoite growing on E. coli