Using sophisticated genetic sequencing, a team of U.S. researchers has confirmed that the strain of cholera now decimating Haiti's population matches samples of the bacteria from South Asia and not those from Latin America.
The scientists, whose findings were published online Thursday by the New England Journal of Medicine, say 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.
"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 principal researcher Dr. Matthew Waldor, an infectious disease specialist at Harvard University. "There is almost sequence identity between the Haitian isolate and the isolate we sequenced from South Asia."
"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 said from Cambridge, Mass.
More than 2,000 people in Haiti have died from the outbreak of cholera, and almost 100,000 have been sickened by the disease since October.
In a report obtained by The Associated Press earlier this week, a French scientist concluded that the cholera outbreak originated in a tributary of Haiti's Artibonite river, next to a UN base outside the town of Mirebalais.
Many Haitians have long suspected the Nepalese base was the source of the disease, and anger at the troops sparked a week of riots in which UN soldiers were injured and several Haitians were killed.
But Waldor said it would take much more investigation to pinpoint ground zero of the epidemic -- and knowing wouldn't change anything.
"Our data certainly doesn't exclude that possibility; it doesn't prove it," he said. "But Nepal is considered part of South Asia."
Cholera, which causes severe diarrhea, vomiting and dehydration, results from a potent infection of the intestine with the bacterium Vibrio cholerae, which is usually found in water or food sources contaminated by feces from an already infected person. The disease has not been endemic in Haiti for about a century.
But its incursion into the island country will likely take years to burn itself out, infectious disease specialists predict.
The South Asian strain is highly virulent; it produces a toxin that causes extremely severe diarrhea compared with other cholera strains and can lead to death within hours if left untreated with antibiotics and rehydration.
"With these strains from South Asia, they seem to be fitter in some ways that we don't fully understand," said Waldor. "So it's a danger that these strains could then spread off the island of Hispaniola and replace strains that are in Latin America.
"So what's worrisome is that this strain, which is more virulent and may be more environmentally fit, could then replace strains that are circulating in Latin America."
Another concern is that the South Asian strain's genes could mutate or its genes could combine with those of other cholera bugs to create a whole new and possibly deadlier strain.
"I don't think we need to even invoke any new mutations ... Just in and of itself, this is a worrisome finding," he said of the strain causing the first cholera epidemic in Haiti in a century.
Dr. Jay Keystone, a tropical disease specialist at Toronto General Hospital, said the bacterium flourishes in places with poor hygiene and inadequate water and sanitation systems, so it's unlikely to become rooted in nearby countries that have such infrastructure in place.
Haiti, still physically in a shambles and politically unstable almost a year after the earthquake, is another story.
"As the country's infrastructure improves and the water supply improves and the sanitation improves, then you're going to see less cholera," Keystone said. "But that's going to be a long time."
Peru had been cholera-free for many decades until 1991, when the bug came ashore in ballast water from ocean-going ships. The disease spread up through South America and into Central America; in Peru, it took more than 10 years until the infection burned itself out, he said.
It could take that long for Haiti to rid itself of cholera too, said Keystone.
Waldor and his colleagues are calling on the World Health Organization to create a policy that would require all UN troops and aid workers to be vaccinated against cholera before deployment to disaster zones like Haiti.
"I think we could prevent this in the future with a vaccine or antibiotics for people who are travelling from areas that are highly endemic, where they're having cholera," he said.
"And if those people are going to go to be part of security forces or relief workers to areas that don't have cholera but are at super-high risk for cholera, such as Haiti, then such people should be screened and-or given a dose of antibiotics or a vaccine that would prevent their transmitting it to people."
"I think it's so simple. It's a simple change that could prevent a future Haiti-like epidemic."
Keystone agrees that peacekeepers and aid workers should have cholera vaccinations before setting out to help in areas rocked by natural or man-made disasters, especially if they come from countries where cholera is endemic.
"You need to protect your troops, but you need to protect the people there from you bringing something that they didn't have," he said.
"It's very sad. The last thing that Haiti needed was cholera."
