Satellite climate data can give advance warning of the spread of infectious diseases such as cholera, writes Claire O'Connell
We blame global climate change for many things, such as melting polar ice and extreme weather.
But what is less well known is that climate and ocean warming can also boost the spread of infectious diseases such as cholera.
We can now use satellite data to read cues from the earth's oceans and predict when certain epidemics are going to hit. This means that we can pre-empt outbreaks and put measures in place to save lives, according to Dr Rita Colwell, a world expert in global infectious diseases who recently visited Ireland.
"We need to recognise signals from climate change and incorporate them into human health so we can be proactive, not reactive," she told a seminar last week organised by the Marine Institute and hosted by the Royal Irish Academy.
Dr Colwell, who holds professorships at the University of Maryland and at Johns Hopkins University Bloomberg School of Public Health, and who chairs Canon US Life Sciences, uses cholera as a model of how infectious disease can be linked closely with the environment.
Cholera brings potentially fatal symptoms of diarrhoea, dehydration and salt imbalances in the body. Caused by the water-borne bacterium vibrio cholerae, it can be a major health problem in areas of the developing world that lack clean drinking water.
Dr Colwell's researchers discovered that the cholera microbe hitches a ride on tiny shrimp-like planktonic animals called copepods in the ocean. In warm seas, large plankton growths or "blooms" support reservoirs of the cholera bug, which can then move into the drinking-water supply. In particular, ocean-warming events like El Niño have been linked with cholera outbreaks, she says.
We can now use satellites to measure sea level, water temperature and the extent of plankton growth, and thus get a warning of impending outbreaks of cholera, says Dr Colwell. "We can predict when, where and how intense an epidemic will be."
Boiling or treating drinking water reduces the risk of contracting cholera and those who get the disease can be effectively treated with an oral sugar and salt solution to combat symptoms.
Consequently, having advance warning of an epidemic could allow protective measures and healthcare supplies to be put in place, potentially saving many lives. "If you know when epidemics are going to occur then you are able to mobilise the healthcare community and to provide education and instructions to the public, which is really critical," Dr Colwell told The Irish Times after her talk.
"For example, in Peru when cholera occurs they put up signposts saying 'boil water'," she says, noting that basic local measures can be highly effective.
When Dr Colwell's group found that cholera was associated with plankton, they developed a new and simple water treatment in a region of Bangladesh, a country where cholera is endemic.
Drinking water is often sourced from ponds or rivers that can contain copepod plankton and other particulates. The researchers found that filtering the water through a folded sari garment before drinking sieves out plankton and cuts cholera infection levels in half.
Dr Colwell laments that sometimes the simple approaches are overlooked in the western world. "We have come to the point in the 21st century where if it isn't complicated then it isn't considered effective."
On the other hand, she says: "We wouldn't have been able to show [ the link between cholera and the environment] if we didn't have the satellites and the molecular biology."
Environmental change can also affect other infectious agents that hit closer to home. Dr Colwell's group has linked warm temperatures in England and Wales with an increased incidence of the food-poisoning bug campylobacter in the water supply, and she believes global warming could increase environmental levels of a water-borne microbe called helicobacter pylori, which is associated with stomach ulcers in the developed world.
"I believe that many human pathogens are going to follow a similar paradigm to cholera," says Dr Colwell, who is setting up an international network to examine infectious diseases.
A former director of the influential US National Science Foundation, she stresses the need for scientists from different disciplines to work together on the complex links between infectious diseases and the environment.
The global view needs input from many areas of research, from studying the genes of single cells to monitoring oceans and processing vast amounts of information. "Understanding [ the complexity] involves observing at multiple scales," she says.