Daijiworld Media Network - Washington
Washington, Jul 20: Climate change is expected to reshape the spread of waterborne diseases rather than increase all of them uniformly, according to a comprehensive new review, which found that rising temperatures could fuel some deadly bacterial infections while reducing the prevalence of several common viral illnesses.
The review noted that warmer water creates favourable conditions for bacteria responsible for some of the world's deadliest gastrointestinal diseases, whereas many viruses that cause diarrhoea and vomiting thrive in cooler, drier conditions and may become less common as global temperatures rise.
The findings suggest that climate change will alter which pathogens pose the greatest threat to different communities, rather than simply increasing the overall burden of disease. Infectious diarrhoeal diseases continue to claim nearly 1.2 million lives every year, with young children accounting for the majority of deaths.
The review was led by Karen Levy, Professor of Environmental and Occupational Health at the University of Washington, whose research focuses on how weather patterns influence the spread of gastrointestinal infections.
Her team analysed decades of research on pathogens transmitted through water contaminated with human or animal waste and found that bacteria and viruses respond differently to changing climatic conditions.
According to the review, warmer temperatures accelerate the growth of many bacteria, including Vibrio cholerae, the bacterium responsible for cholera, which multiplies rapidly in warm, slightly saline water.
By contrast, viruses such as norovirus, rotavirus and adenovirus, which commonly cause diarrhoea and vomiting, spread more efficiently during cooler and drier seasons. As these periods become shorter due to global warming, infections caused by several of these viruses may decline.
The analysis also found that bacterial gastrointestinal infections generally increased with rising temperatures, while viral infections showed a declining trend. The risk of Salmonella infection, for instance, rose by around five per cent for every one-degree Celsius increase in temperature.
The review highlighted extreme rainfall and flooding as major drivers of waterborne disease outbreaks. Heavy rain can overwhelm drainage and sanitation systems, allowing human and animal waste to contaminate rivers, lakes and drinking water sources.
One of the most notable examples occurred in 1993, when the parasite Cryptosporidium contaminated the water supply in Milwaukee, United States, after spring runoff overwhelmed a water treatment plant. The outbreak infected an estimated 400,000 people, making it the largest recorded waterborne disease outbreak in US history.
However, researchers noted that the relationship between rainfall and disease transmission is complex. Heavy rainfall following prolonged dry periods tends to wash accumulated contaminants into water sources, increasing disease risk, whereas rainfall during already wet periods may dilute pathogens and reduce transmission.
The review also warned that drought poses a significant but often overlooked threat to public health. As wells and streams dry up, communities are forced to rely on unsafe water sources, store water for longer periods and reduce water use for hygiene practices such as handwashing.
A study involving children from dozens of low- and middle-income countries found that six months of drought increased the risk of diarrhoeal disease by approximately five to eight per cent. The greatest increases were observed among households with limited access to water or soap.
Rising sea levels present another challenge, particularly in low-lying coastal regions. Saltwater intrusion into groundwater and ponds creates conditions favourable for cholera bacteria. In parts of coastal Bangladesh, increasing salinity and storm surges have already been linked to worsening health outcomes.
Despite the challenges, the researchers stressed that effective preventive measures already exist.
They recommended strengthening water supply and sanitation systems capable of functioning during floods and extreme weather events, improving disease surveillance to identify specific pathogens quickly, and expanding access to vaccines against waterborne diseases such as cholera, rotavirus, typhoid and hepatitis A.
The review also cautioned that climate-related disasters can disrupt vaccine storage by damaging electricity supplies needed for refrigeration.
Elizabeth Carlton, Professor at the Colorado School of Public Health at the University of Colorado Anschutz Medical Campus and co-author of the review, said climate change was fundamentally altering the way waterborne diseases spread.
She noted that while the tools needed to respond already exist, the greater challenge lies in adapting and deploying them effectively to meet changing climatic conditions.
The researchers concluded that as climate change reshapes disease patterns, the most effective protection will come from tailoring water infrastructure, disease surveillance and vaccination programmes to the evolving risks faced by individual regions.