by Peter Orengo

A cholera epidemic is expected during the El NiÒo rains, scientists say.

Cholera is not only linked to climate change, it also has an El NiÒo angle, research finds.

El Nino — the periodic flow of warm seawater across the surface of the central and eastern Pacific Ocean — can lead to higher atmospheric temperatures and heavy rains.

When these conditions are coupled with the rise in temperature and heavy rainfalls caused by climate change, ideal conditions are created for the bacterium that causes cholera to multiply, bringing about a global resurgence of the disease.

Floods contaminate water with the cholera bacterium. Photos: Benjamin Sakwa

A World Health Organisation (WHO) study found that during the 1997-98 El NiÒo, a rise in sea surface temperature coupled with excessive flooding caused cholera epidemics in East Africa Bangladesh and Mozambique.

The Intergovernmental Panel for Climate Change (IPCC) cited research in Bangladesh, led by distinguished US scientist Rita Colwell in the late 1990s, which established the link between the cholera bacterium, sea surface temperature and phytoplankton.

Ms Jane Oluoch, a senior environmental science lecturer at the University of Pretoria, says besides the biological factors, "Floods contaminate drinking water with the bacterium."

Warmer surface temperatures increase the abundance of phytoplankton, which supports a large population of zooplankton — animal-like microorganisms, which serves as a reservoir for the waterborne disease.

Colwell and her colleagues also traced the source of the cholera bacterium to the plankton in rivers and estuaries.

Studies in Africa, led by Miguel ¡ngel Luque Fern·ndez from the Institute of Health Carlos III, based in Spain, were the first to show a link between higher temperature and rainfall and the incidence of cholera.

The study, published in the Transactions of the Royal Society of Tropical Medicine and Hygiene, on cholera outbreaks between 2003 and 2006 in Zambia showed that a one-degree Celsius rise in temperature six weeks before an outbreak began allowed the bacteria to multiply leading to almost five per cent more cholera cases. A 50mm increase in rainfall three weeks ahead of an outbreak pushed up the number of cases by more than two per cent. "My hypothesis, which we are in the process of testing, is that climate changes — sea surface temperature, sea surface height, rainfall — have influenced the cholera epidemics in East Africa, notably Mozambique," Colwell wrote.

Zimbabwe, a landlocked country bordering Mozambique in southern Africa, recorded one of the world’s worst cholera outbreaks in 2008, with more than 4,000 deaths.

Last month the Metrological Department alerted the country to brace for an El Nino.