New evidence published in mBio this week provides strong evidence that United Nation’s peacekeepers brought a cholera epidemic to Haiti.
Haiti has had a terrible history of hardship, but 2010 was an annus horribilis. In January of that year, an earthquake laid flat many parts of Haiti killed hundreds of thousands of people and devastated the country’s already fragile infrastructure. In October, a cholera outbreak turned matters from bad to worse. The outbreak sickened nearly 250,000 and resulted in a reported 4,670 deaths, causing widespread panic and complicating relief efforts. Rumors quickly spread that the disease was brought to Haiti by United Nations peacekeepers from Nepal, but until now the suspicion remained unconfirmed.
A team of researchers from Nepal, Denmark, and the United States used whole genome sequence typing to compare the genomes of 24 recent Vibrio cholerae isolates from Nepal with V. cholerae strains from all over the world, including three from the Haitian outbreak. Whole genome sequence typing can reveal evolutionary relationships among a set of strains.
The results were pretty clear, according to Paul Keim of Northern Arizona University and the Translational Genomics Research Institute, an author on the study. “We found that the Haiti isolates and certain Nepal isolates had a very close evolutionary relationship – they’re essentially identical at the whole genome level.”
“It seems likely that it came from Nepal,” says Keim.
Earlier studies of the Haiti strains failed to identify the source of the country’s outbreak. Keim says the discrimination power of whole genome sequence typing makes the conclusions of the study very compelling.
Until last year, Haiti had not seen an outbreak of cholera in a hundred years. Investigations into the source of this outbreak noted that it seemed to ignite about a week after a battalion of Nepalese troops arrived at a UN compound near the town of Mirebalais. It was alleged that sewage from the base was illegally dumped in the Artibonite River and began the outbreak. These latest results seem to uphold this version of events. Cholera is endemic in Nepal and an outbreak began there in September 2010, shortly before the Nepalese troops left for Haiti in October. V. cholerae can be carried in the gut of individuals exposed to the illness – even in individuals who do not become ill themselves.
Asked why the investigation into the origins of the Haiti strains took so many months, Keim cites problems getting access to samples of V. cholerae from both Nepal and Haiti. “It is a politically charged environment and it was very difficult to get the strains that were necessary for the study. Nobody wants to be accused of having spread a devastating disease to a disaster zone.” Keim credits Nepal’s Ministry of Health for stepping up to help and providing samples from their country.
One weakness of the study, according to Keim, is the small set of global V. cholerae genome sequences available for comparisons. The lack of access to a set of global V. cholerae strains and sequences seriously constrains efforts to identify the source of cholera outbreaks. “What this area needs is global cooperation and sharing of data and strains to be able to definitively identify sources,” says Keim.
The situation that apparently played out in Haiti is tragic, but the transfer of disease from one country to another is hardly unique. Pathogens are carried across international borders all the time, and there are currently few barriers to their movements, says Keim. “It’s hard to imagine, in the developed world, that we could actually screen all the people coming and going in airplanes, but in disasters we have a little more control. We need to get better at screening people, especially people coming into disaster areas.”