Cholera kills thousands of people every year. It's a diarrhoeal illness caused by a bacterium, Vibrio cholerae, which is carried harmlessly in the intestines and on the surfaces of copepods - small marine animals or zooplankton that live in the sea and estuarine waters. These organisms feed on marine plants and algae called phytoplankton.
Periodically, warm sea temperatures, a sudden influx of nutrients washed into the water from the land, or a combination of the two provokes a surge in the growth of the phytoplankton, which in turn triggers population explosions or "blooms" amongst the cholera-carrying copepods. This is then followed by a local outbreak of cholera amongst humans, who then spread the disease amongst themselves. By the time sufficient medical help can be marshalled, the number of cases and fatalities can be very high.
But now University of Maryland researcher Rita Colwell has shown that it's possible to predict where outbreaks are going to occur by using satellites to spy on what the plankton are doing.
"The warmer sea temperatures, and green chlorophyll in the phytoplankton, can both be seen using a satellite," she explains. "This enables us to pre-empt the location of future cholera outbreaks by two to three months," meaning that preventative medical management can be put in place on the ground to stem an outbreak.
The research is highly significant because the warmer sea temperatures predicted by climate models of global warming mean there are likely to be far more plankton blooms in future.