La Niña plus the plunge in water and sanitation quality following January's earthquake may be to blame
Flickr/United Nations Development Programme
[SANTIAGO] Weather conditions — not UN soldiers — may have triggered Haiti's cholera epidemic, which has killed more than 1,000 people in less than a month, three leading researchers have told SciDev.Net.
A coincidence of several catastrophic events — from climatic changes caused by the ocean-atmosphere phenomenon La Niña, to the plunge in water and sanitation quality following Haiti's disastrous January earthquake — provide the most likely explanation for the outbreak, which has hospitalised 17,000 people.
The outbreak suddenly appeared in small communities along the Artibonite River, 60 miles north of the capital Port-au-Prince, on 21 October.
Its origin has not been determined with certainty but the popular belief is that the disease arrived with infected UN soldiers from Nepal. They were stationed in a rural base near the river where the outbreak first started.
Cholera is endemic in Nepal whereas Haiti has not had a recorded cholera case in the last 50 years.
The US Centers for Disease Control and Prevention said in a press release earlier this month (1 November) that genetic analysis of the cholera strain that hit Haiti reveals that it most closely matches South Asian strains, which further fuelled the suspicion.
But scientists SciDev.Net talked to all rejected the idea that cholera was imported from Nepal.
"Vibrio cholerae, the bacterium responsible for cholera, may have been dormant in water until weather-related conditions caused it to multiply enough to constitute an infective dose if ingested by humans," said David Sack, a cholera specialist at Johns Hopkins University Bloomberg School of Public Health, United States.
Rita Colwell, a professor at the University of Maryland, United States, agreed that the aquatic environment conditions produced by a strong La Niña this year may have made cholera flare up in Haiti for the first time in 50 years.
Colwell's research aims to predict cholera outbreaks by correlating disease occurrence with weather patterns, water surface temperatures and algal blooms (on which crustaceans that house the bacteria feed).
She has found that the annual patterns of higher sea temperatures along the coast correlate with patterns of cholera cases in both Bangladesh and Peru, based on data from 1992–1995 and 1997-2000, respectively.
Weather conditions do not have to be present together with poor sanitation and lack of clean water for an epidemic to occur, she said, but the latter increase chances of an outbreak. Cholera spreads when faeces from infected humans, who may not present any cholera symptoms, get into drinking water that other people consume.
"Diarrhoeal diseases exist in Haiti. The difference now is that several catastrophic events have occurred practically at the same time, exacerbating conditions of poverty."
Afsar Ali, an associate professor of environmental and global health at the University of Florida, United States, agrees that climatic factors promoted the bacteria's multiplication in the Artibonite area. He told SciDev.Net that when he visited Haiti in August, refugees from the earthquake were using water directly from the river and ocean.
Since V. cholerae favour estuarine water, where the tide meets the stream, he warned at that time of the risk of a cholera epidemic.
"Interestingly, the refugees got cholera first. If, as it is likely, cholera was already present in the Haitian coastal region, permanent residents exposed to low levels of the cholera bacterium for prolonged periods of time would logically have more immunity than refugees."
The climate-cholera link in Haiti may be confirmed if, as Colwell believes, the epidemic weakens in winter as the waters in the Caribbean cool down.
Alejandro Krimer ( Argentina )
22 November 2010
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