Science Interviews

Predicting Cholera Outbreaks from Space

Ben - And now to a disease that kills thousands of people every year - most of them in the developing world - and that's the bacterial infection cholera, which causes life-threatening diarrhoea.  Most people pick it up by drinking contaminated water, because the cholera bacterium normally lives in the intestines of marine creatures like plankton. So increases in plankton numbers due to global warming and rising sea temperatures could cause the number of cases of cholera to surge.  But watching the plankton also means that scientists now have a way to spot where outbreaks might be about to happen - and they're using satellites to do it.

Meera - We’ve all heard about climate change in the news: increasing temperatures, melting glaciers and rising sea levels. But one factor we don’t hear about is the effect climate change can have on human health and pandemics. A bacterial disease now thought to be exacerbated by climate change is cholera, caused by the bacterium Vibrio cholerae. One scientist that’s been researching this is Rita Colwell from the University of Maryland and John Hopkins University.

Rita - Cholera is caused by a bacterium that is found naturally in the environment of estuaries, coastal waters, lakes, rivers and even offshore areas. It’s associated with plankton. Much like we have in our gut bacteria help us digest food, so do these zooplankton have in their gut and on the surface of their structures. The Vibrio that unfortunately also causes cholera in humans when ingested.

Meera - Initially cholera only affected the Indian subcontinent but through land and sea trading it spread worldwide. The main prevention is by filtering and chlorinating water supplies. This has largely removed the problem in developed countries.

Rita - The areas that are affected mostly are the developing countries: India, Bangladesh, Malaysia, countries in the Middle East and Far East and countries where sanitation, safe drinking water are not available to all. That is the biggest problem, safe drinking water.

Meera - So we now how and where cholera occurs but how is it possible to look into the future and predict when an outbreak is coming?

Rita - The capacity to predict when outbreaks will occur has been made possible by the relationship between the bacterium, the zooplankton species that ?? and the phytoplankton that bloom first followed by the zooplankton. The phytoplankton can be measured using chlorophyll measurements using sensors in satellites so that allows us to have a global predictive capacity for cholera. That allows us to have a head start in knowing when the epidemic will occur. That allows us to develop what I call pre-emptive medicine. That is to be able to go in with the sufficient vaccine as needed with warnings: public health measures that can be taken. That allows us then to pre-emptively prevent. That’s very important.

Meera - It is great to be able to predict and prevent an outbreak but how far ahead can we realistically predict?

Rita - At the present time the factors that we have bee studying, particularly early observations of chlorophyll concentrations that predict subsequent zooplankton blooms, certainly between 2-3 months would allow us a head-start in predicting an outbreak.

Meera - In its severity cholera can be fatal but up to 80% of cases can be treated. The important thing to note about this disease is that it is preventable if known about, mainly through clean water supplies and sanitation. This isn’t always possible in the developing world so the ability to predict an outbreak and therefore raise community awareness and provide health education in advance could greatly reduce the number of people infected with the disease.

Ben -   So first the marine plants bloom, which scientists can see from space, and this is followed by a surge in the growth of the plankton which carry cholera, which can then lead to an outbreak of the disease.  So by watching what the plankton are doing you can predict where the disease will strike next.  That was Meera Senthilingam talking with cholera researcher Rita Colwell.

March 2008