Global warming could increase diseases originating from water sources

WASHINGTON (AFP) – Climate change could increase exposure to water-borne diseases originating in oceans, lakes and coastal ecosystems, and the impact could be felt within 10 years, US scientists told a conference in Washington on Saturday.

Several studies have shown that shifts brought about by climate change make ocean and freshwater environments more susceptible to toxic algae blooms and allow harmful microbes and bacteria to proliferate, researchers from the National Oceanic and Atmospheric Administration said.

In one study, NOAA scientists modeled future ocean and weather patterns to predict the effect on blooms of Alexandrium catenella, or the toxic "red tide," which can accumulate in shellfish and cause symptoms, including paralysis, and can sometimes be deadly to humans who eat the contaminated seafood.

"Our projections indicate that by the end of the 21st century, blooms may begin up to two months earlier in the year and persist for one month later compared to the present-day time period of July to October," said Stephanie Moore, one of the scientists who worked on the study.

But the impact could be felt well before the end of this century -- as early as 2040, she said at the annual meeting of the American Association for the Advancement of Science (AAAS).

"Changes in the harmful algal bloom season appear to be imminent. We expect a significant increase in Puget Sound (off the coast of Washington state where the study was conducted) and similar at-risk environments within 30 years, possibly by the next decade," said Moore.

In another study, NOAA scientists found that desert dust that is deposited into the oceans from the atmosphere could also lead to increases of harmful bacteria in seawater and seafood.

Researchers from the University of Georgia found that adding desert dust, which contains iron, to seawater significantly stimulated the growth of Vibrios, a group of ocean bacteria that can cause gastroenteritis and infectious diseases in humans.

"It is possible this additional input of iron, along with rising sea surface temperatures, will affect these bacterial populations and may help to explain both current and future increases in human illnesses from exposure to contaminated seafood and seawater," the researchers said.

"Within 24 hours of mixing weathered desert dust from Morocco with seawater samples, we saw a huge growth in Vibrios, including one strain that could cause eye, ear and open wound infections, and another strain that could cause cholera," said Erin Lipp, who worked on the study.

The amount of iron-containing dust that is deposited in the sea has increased over the last 30 years and is expected to continue to rise, based on precipitation trends in western Africa which are causing desertification.

Meanwhile, researchers at the University of Wisconsin-Milwaukee warned that an increase in severe rainstorms could cause more sewage overflows, which would release disease-causing bacteria, viruses and protozoa into drinking water and onto beaches.

The researchers in this study used climate models to show that spring rains are expected to increase in the next 50 years, and with that increase, ageing sewer systems are more likely to overflow because the ground is frozen and rainwater can't be absorbed.