Hong Kong - Moderate increases in temperature and rainfall can herald cholera epidemics, a study in East Africa has found, and researchers urged governments to use those environmental cues to better protect vulnerable populations.
The researchers matched cholera outbreaks which occurred in Zanzibar between 1999 and 2008 against temperature and rainfall records over the same period and found that the environmental changes were closely followed by disease.
“We found that when temperature goes up by 1 degree Celsius, there is a chance of cholera cases doubling in four months' time and if rainfall goes up by 200 millimetres, then in two months' time, cholera cases will go up by 1.6 folds,” Mohammad Ali, a senior scientist at the International Vaccine Institute in Seoul, South Korea, said by telephone.
Governments can use these environmental cues to introduce early interventions like vaccinations, he said.
“It can be used as a predictive tool and an early warning system,” said Ali, a member of the research team which published their findings in the American Journal of Tropical Medicine and Hygiene on Wednesday.
Cholera has emerged once more as a public health threat because of the dominance of the El Tor strain that causes serious disease. Well adapted to human habitats, it causes longer outbreaks that last for months, even years.
In Haiti, a cholera epidemic that started in October 2010 after a deadly earthquake has killed 5,000 people and the embattled country is preparing for fresh cholera outbreaks with the start of the rainy season.
Cholera sickened more than 220,000 people around the world in 2009, killing almost 5,000 of them, according to the World Health Organisation.
The cholera bacteria reside in sea organisms called copepods. Rises in sea temperature lead to a proliferation of copepods, which in turn helps the cholera bacteria multiply.
“When temperature goes up, cholera bacteria in the ocean environment multiply ... Oceans meet ponds and rivers and then humans (get infected),” Ali said.
Cholera is transmitted through consuming contaminated food and water. It causes severe diarrhoea, dehydration and even death if the patient is left untreated.
Peter Hotez of the American Society of Tropical Medicine and Hygiene, who was not involved in the study, said health experts need to reconsider ways to deal with cholera epidemics, which are lasting longer than before.
“This paper implicates that global warming and climate change may have a key role, it also means we need new tools to combat cholera epidemics,” Hotez said.
“In the past, the dogma has been there's no time to vaccinate because the epidemic will burn itself out. But now with protracted epidemics, we should stockpile the cholera vaccine,” Hotez said by telephone. - Reuters