Scientists reported Thursday the strongest evidence yet that a cholera outbreak that has killed more than 2,000 people in Haiti can be traced to South Asia.
The analysis fits with, but does not prove, the controversial idea that the disease came from U.N. troops dispatched from that region.
DNA analysis found that cholera bacteria recovered in Haiti were nearly identical to strains predominant in South Asia, and different from those found in Latin America, researchers said.
That indicates that cholera was introduced by people, rather than arriving through ocean currents or arising within Haiti, as has been suggested, said Harvard researcher Dr. Matthew Waldor.
The most likely explanation is that the germs were released in excretions from people, but they could also have come from contaminated food or water brought in by people arriving from South Asia, he said.
Waldor is an author of a report published online Thursday by the New England Journal of Medicine. The paper confirms a South Asian link reported last month by the U.S. Centers for Disease Control, and presents a more detailed analysis of the DNA.
Cholera has sickened nearly 100,000 people in Haiti since October, and it's feared the germ could infect six times that number. Before the current outbreak, no cholera had been confirmed in Haiti since World Health Organization record keeping began in the mid-20th Century. And no cases had been suspected for at least a century.
The origin of the outbreak became politicized with suspicions that U.N. soldiers from Nepal brought the disease to Haiti and transmitted it because of sanitation problems at their base. The suspicions were strengthened when sanitation problems and questionable human waste-dumping practices were found by journalists.
A week of anti-U.N. riots broke out. Riots are again raging in Haiti over a disputed political election and clashes with U.N. peacekeepers are a constant occurrence.
Waldor said his report is consistent with the Nepalese-troops hypothesis, but does not prove it or deal directly with it. The researchers didn't compare the Haitian samples with those from Nepal or test Nepalese troops stationed in Haiti, he noted.
The researchers may examine cholera strains from Nepal and elsewhere around the world to get a better idea of where the Haitian cholera came from, he said.
While the evidence is strong that human activity brought cholera to Haiti, 'we don't need to really indict any particular human group,' Waldor said.
Dr. John Mekalanos, another study author from Harvard, said he'd like to do enough additional DNA research to trace the Haitian strain to a particular country, be it Nepal or some other nation.
'This fact simply will prove that the travel of infected individuals to areas that are at risk for epidemic cholera needs to be addressed as a public health concern,' he said.
The World Health Organization, the United Nations and the U.S. CDC have said pinpointing the outbreak's origin was unimportant, likely impossible and counterproductive to fighting the disease. Several epidemiologists and public health experts, however, have said seeking the origin was important for scientific and social reasons, in Haiti and globally.
In any case, Waldor said the finding that the germ was brought in by outsiders suggests that preventive steps should be taken whenever troops or relief workers are sent to a disaster scene from a nation where cholera is widespread. Such people should be routinely screened for the disease or given antibiotics or a dose of vaccine, he said.
The new study says it's important to try to keep Haiti's cholera from spreading elsewhere. Waldor said evidence suggests that if the Haitian strain reached Latin America, it might replace the local strains and cause a more severe and lethal disease in that region.
So that provides further rationale for a large cholera vaccine campaign in Haiti, he said, although he noted that is 'not immediately possible' because the vaccine is in short supply. Perhaps production could be stepped up over the next few months, he said.