Study finds Haitian cholera strain resembles one from South Asia, carries mutation that increases severity

Dec 13 2010

"Detailed genetic tests confirm that the cholera strain that has killed more than 2,000 people in Haiti came from South Asia and most closely resembles a strain circulating in Bangladesh," according to a study published Thursday in the New England Journal of Medicine (NEJM), Reuters reports (12/9).

According to the research, "the South Asian cholera bacteria strain was probably introduced into Haiti by an infected human, contaminated food or another item brought to the island country after January's devastating earthquake," the Canadian Press/CTV News writes.  

"Our evidence is extremely strong, based on the full genome sequence of two Haitian isolates as well as isolates from Latin America and South Asia," said Matthew Waldor, the study's lead researcher and an infectious disease specialist at Harvard Medical School. "There is almost sequence identity between the Haitian isolate and the isolate we sequenced from South Asia," he said. "This is distinct from Latin America, and together those data suggest that this strain then didn't wash up from the shores of Central or South America onto the shores of Haiti through some environmental event, but instead was transported most likely by a human from a South Asian nation to Haiti," Waldor noted (12/9).

"The analysis fits with, but does not prove, the controversial idea that the disease came from U.N. troops dispatched from" Nepal, according to the Associated Press. "The researchers didn't compare the Haitian samples with those from Nepal or test Nepalese troops stationed in Haiti, [Waldor] 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," the news service reports.

Another co-author on the study from Harvard, John Mekalanos, expressed interest in conducting additional DNA research to trace the Haitian cholera strain to a specific country. "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," Mekalanos said (12/9).

"Mekalanos and colleagues said they also confirmed that Haiti's cholera strain carries a mutation associated with causing more severe disease," according to Reuters. "Our genome data puts the Haiti strain in the group that is the worst of the worst," Mekalanos said (12/9).

"The researchers call for global health officials to consider mass vaccination not only to control the spread of cholera among the Haitian people but also to reduce the chance that the mingling of different cholera strains in the Caribbean region could produce a more virulent strain that could cause much greater harm. Their study also points to the benefit of immunizing individuals who travel from areas where cholera is present to regions where it is absent but that may be at risk for an epidemic," a Harvard Medical School press release states (12/9). Waldor said, "In the future when people go to work in disaster zones ... they should be screened or just presumptively given a dose of antibiotics or a vaccine so that they will not transfer cholera," Reuters writes (12/9).

More Support For Cholera Vaccination Campaign In Haiti, Neighboring Countries As New Information Emerges

Meanwhile, NPR's Morning Edition reports that public health leaders are calling for cholera vaccination campaigns in Haiti and neighboring countries in light of new information about the amount of vaccine available.

"Until now, experts felt that there wasn't enough vaccine to be effective and that a vaccination campaign would distract from efforts to treat the thousands with the disease. But a consensus is emerging around the idea that the vaccine is urgently needed," NPR writes. "One factor behind the shift: The Pan American Health Organization [PAHO] has discovered far more vaccine is out there than previously thought."

Manufacturers might have stored more than one million doses of cholera vaccine, according to John Andrus, deputy director of PAHO. "That's new information to us and that basically changes our thinking," he said. Vaccination campaigns should be carried out in Haiti and the Dominican Republic, as well as other places, Andrus said. "I see a real opportunity to vaccinate vulnerable groups in countries that have yet to see the outbreak but we know would be very vulnerable if cholera was imported," he said. "I worry about some of the poorer countries of the Caribbean. I worry about Central America," Andrus added. "He would also consider vaccinating people traveling to these areas if they are living in countries where cholera outbreaks [are] already going on," NPR writes. The article also looks at how Thursday's NEJM study and other findings are fueling the call for vaccination (Knox, 12/10).