UNDERSTANDING NAEGLERIA FOWLERI
A Different Type of Pathogen, An Increasing Climate Change Threat
Publication Date (Web): 1 May 2017
As Australians, we are used to dealing with warmer climatic conditions, and over the last six months we have seen a number of climate records being broken. With our changing climate these extremes are likely to become more common and more records are likely to be broken. Climate change is also bringing a number of challenges to the water industry, and one of those is an increasing water temperature profile and the risk of a unique and dangerous pathogen, Naegleria fowleri.
So what is Naegleria fowleri? Why does it require more attention from our industry, and why will climate change increase the risk associated with this pathogen?
Naegleria is a natural environmental organism (free moving amoeba) that lives in fresh warm water conditions, with an optimal growth temperature at around 45oC. Also unlike most of the water borne pathogens of concern, it is not related to faecal contamination. If the surrounding environmental conditions support the amoeba, it can be carried by dust, soil, minor infiltration, and could contaminate susceptible potable water supplies.
Environmental Conditions on Naegleria fowleri (CDC 2015)
Naegleria fowleri, has a unique behavioural trait, which when exposed to the human nasal track will move up the olfactory nerve, through the cribriform plate and then into the brain. Due to our warm body temperatures and organic material availability, the organism starts to feed on the brain tissue. This infection causes brain swelling and tissue deterioration and is called Primary Amoebic Meningoencephalitis (PAM). In the great majority of cases (greater than 97%) death occurs within one to two weeks of infection, however the occurrence of the disease is currently considered rare. Within the United States there have been 138 cases of PAM between 1962 and 2015, with 0 to 8 infections per year (CDC – April 22, 2016, https://www.cdc.gov/parasites/naegleria/infection-sources.html) .
Infographic: How a tiny amoeba can eat your brain
The majority of PAM cases worldwide occur due to exposure to contaminated recreational water. However, in Australia we also have conditions that can warm water potable supplies. Potable water which is continually above 25oC or seasonally above 30oC is considered at risk (Australian Drinking Water Guidelines 6; Version 3.2 2016, pages 322 – 323).These type of warm water conditions are not limited to northern or inland regions of Australia, but to any region or location with warm water conditions such as deep geothermic bores, external reservoirs and long exposed pipelines.
An in-depth Australian study was undertaken by M.Dorsch in 1982 on PAM in potable water supplies (Primary Amoebic Meningoencephalitis: An Historical and Epidemiological perspective with Particular Reference to South Australia, 1982). During her research Dorsch identified 19 fatal Australian PAM cases from 1955 to 1981, and she looked at a number of different water schemes and disinfection controls.
The key finding from Dorsch was that by maintaining a free chlorine residual of 0.5 mg/L throughout the entire reticulation system, the pathogen could be effectively managed. The key findings from the Dorsch 1982 study has provided the basis for the recommendations within the current ADWGs, which includes a dedicated factsheet on the pathogen.
The United States has also recently experienced potable water related PAM infections for the first time in many years. The U.S. Centers for Disease Control and Prevention (CDC) also deem this an increasing pathogenic risk with the increasing climate temperatures. Current recommendations from the CDC reflect the original Australian recommendations of increased chlorine residuals. However, new research is being undertaken in the United States aiming at providing Chlorine Contact time (Ct) and UV dose levels for inactivation (Inactivation of Naegleria fowleri by chlorine and ultraviolet light; Sarkar and Gerba, 2012).
Within our industry there are a number of water authorities that are monitoring and actively managing the risk of Naegleria fowleri. The general approach taken in managing this pathogen, as per the ADWG, is to initially understand your water system temperature profiles to determine if you do have an at-risk supply. Following which, a study or more routine testing is recommended. Mitigating potential risks are generally based on maintaining clean pipelines and reservoirs, reducing sludge and biofilm layers which can create ideal environments for the amoeba to shelter and colonise, as well as maintaining a free chlorine residual of above 0.5 mg/L throughout the entire reticulation system.
As we head into a future of increased and extreme temperature events, this pathogen is likely to spread throughout our already-warm continent. Within the industry, we currently have the tests, tools and systems to manage this pathogen, however, increasing the awareness and understanding of this deadly amoeba is important to ensure that the risks are understood and mitigated appropriately.
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