Waterborne viruses which have adapted to warmer environments remain infectious for longer and are more resistant to disinfectants such as chlorine, a study by Swiss scientists suggests.

“This implies that microbial water quality may be worse in warm regions, and the health risks posed by viruses will be greater,” Tamar Kohn, associate professor of environmental chemistry at Swiss Federal Institute of Technology in Lausanne, told The Independent.

Sunlight, high temperatures and other microbes can all deactivate viruses found in surface water, reducing their ability to spread disease. However, scientists expect the way viruses react to their environment will evolve in response to climate change.

The Swiss study examined how enteroviruses, a family of viruses which can cause a range of infections including colds, polio and foot-and-mouth disease, may adapt to shifts in conditions. Enteroviruses are typically transmitted through faeces and find their way into the environment through sewage, wastewater and poor sanitation.

The team created four different populations of a human enterovirus by incubating samples in flasks of lake water at 10C and 30C, with and without exposure to sunlight. They then exposed the samples to heat and disinfectant.
The study, published in the American Chemical Society’s Environmental Science and Technology journal, found the warm-adapted viruses were more resistant to being deactivated by heat than the ones incubated in cold water. When moved to cool water, the warm-adapted viruses also remained active longer and withstood exposure to chlorine better.
The findings suggest viruses in warmer waters “will persist in an infectious state for a longer time, and also be more resistant to disinfection”, Prof Kohn said, though she cautioned the laboratory study had yet to be validated in the field.

It means global warming could put people more at risk of infection from swimming in or eating foods irrigated by contaminated water.

While the 3C rise in average global temperature forecast by climate scientists by the end of the century may not be large enough in itself to impact on virus stability, Prof Kohn said, the accompanying rise in extreme weather may bring with it a heightened disease threat, particularly in hotter countries.

“We are mainly thinking of the more frequent occurrence and longer duration of extreme heat waves, which could lead to significant warming of water bodies in the affected areas,” she added.

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