A Vibrio cholerae bacterium

Janice Carr/CDC

Climate variability and increases in rainfall influence the risk of cholera outbreaks in Africa, say researchers.

This information could be used to develop a 'cholera early-warning system', predicting outbreaks by integrating real time weather monitoring with information about factors causing disease and population characteristics.

The study, by researchers from the French Laboratory of Genetics and Evolution of Infectious Diseases (GEMI), was published in the journal BMC Infectious Diseases.

Africa is the continent most affected by cholera, write the authors; more than 95,000 cases were reported in 2004.

Cholera outbreaks are caused by the bacteria Vibrio cholerae. When ingested — usually in contaminated water — they produce a toxin that causes acute diarrhoea.

To better understand the dynamics of cholera epidemics and their link with climate variability, the researchers compared cholera cases from 1975–1995 in five non-endemic countries along the tropical Atlantic coast of Africa —Benin, Cote d'Ivoire, Ghana, Nigeria and Togo — with rainfall over the same period.

In all five countries, they found cholera outbreaks synchronised with increases in rainfall in cycles of 2–5 year periods.

The results were similar to those obtained in similar studies in Bangladesh and Peru.

"The influence in rainfall increase on cholera outbreaks can best be explained by flood waters in disease transmission," write the authors.

"On the scientific level, this work is very interesting," says epidemiologist Didier Bompangue from the Democratic Republic of Congo.

But he adds that the study does not yet answer operational questions such as when to intervene, in what context and how. 

Renaud Piarroux, professor of parasitology and head of the Health and Rural Environment team at the University of France-Comté in France, who has worked in Africa, emphasised that because the study looked at coastal populations, it may not explain outbreaks further inland.

"It is important that research is carried out where the problem is, both in coastal area, as well as in the areas far away from the coast," he says.

Link to full paper in BMC Infectious Diseases

Reference: BMC Infectious Diseases 7, 20 (2007)