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MANILA, PHILIPPINES [TAC] – A team of researchers urged an evaluation of water safety rules following their findings that gut viruses persist in water amoebae.
According to their findings, human norovirus and adenovirus, two major causes of viral gastroenteritis, can persist for extended periods inside free-living amoebae that are common in natural and engineered water systems.
The study, led by Karl Landsteiner University in Austria, with partners from Canada, Australia and Asia, revealed that gut viruses can hide within different stages of the amoebae and remain capable of causing infection after this detour. These free-living amoebae may act as previously overlooked reservoirs and transport vehicles for enteric viruses which could explain their persistence and now provide a basis for more refined risk assessment for safer drinking and recreational waters.
Diarrhoeal diseases caused by contaminated food and water still represent a substantial global health burden despite marked progress in sanitation and drinking water treatment.
Human norovirus is the most common cause of acute viral gastroenteritis globally and can cause infections after exposure to only a handful of viruses while human adenoviruses are frequently detected in sewage and surface waters impacted by wastewater.
Standard water safety concepts focus largely on freely floating viruses in the water. But now the free-living amoebae, single-celled organisms ubiquitous in water systems and long known to shelter bacteria and other microbes, have been recognized as carriers of viruses as well.
Against this backdrop, the researchers set out to clarify how norovirus and adenovirus interact with the different amoeba species and what this might mean for water-related infection risks.
“In water microbiology we have long known amoebae as hosts for bacteria such as Legionella, but their role for human gut viruses has been largely overlooked,” says Dr. Mats Leifels, scientific staff in the Department of Water Quality and Health at KL Krems and first author of the study.
“Our experiments show that common amoebae do not simply digest these viruses – they can protect and transport them, and, in the case of the adenovirus, may even support early steps of viral reproductive activity,” Leifels said.
In his view, this cohabitation between protozoa and enteric viruses adds an important layer to how scientists think about waterborne transmission pathways and the effectiveness of treatment processes.
Rethinking water protection
Free living amoebae are highly resilient organisms. In their dormant cyst form they can survive high doses of disinfectants such as chlorine and monochloramine as well as ultraviolet treatment. If enteric viruses are taken up and sheltered by amoebae, they may therefore bypass some of the barriers that water treatment and sanitation systems rely on.
“From a risk assessment perspective, we have to treat free-living amoebae as potential reservoirs and transport vehicles – “viral Trojan horses” – when we model how long viruses persist in water and how effectively we remove them,” explains Prof. Andreas Farnleitner, head of the Department of Water Quality and Health at KL Kreams and co-author of the study. “Only then our water safety plans can reflect the full complexity of real systems.”
As climate change, urbanization and water scarcity increase the pressure on surface and groundwater resources, understanding such hidden microbial interactions becomes ever more important.
The authors emphasize that their findings are based on laboratory model systems and that further work is needed to quantify amoebae-associated virus loads in real-world waters.
Nevertheless, they see a clear case for including free-living amoebae in future water safety and reuse guidelines and for developing monitoring approaches that can distinguish between truly inactivated viruses and those shielded within protozoa.
