10 December 2010

Haiti cholera came from Asia

Detailed genetic tests confirm that the cholera strain that has killed more than 2,000 people in Haiti came from south Asia.


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, US researchers reported.

While they cannot trace who or what precisely carried the cholera to Haiti, the team at Harvard Medical School and Pacific Biosciences of California Inc say their findings show extra measures may be needed to help prevent the spread of cholera from one disaster area to another a contentious issue because many Haitians have blamed the outbreak on Nepalese troops sent to help them as part of a United Nations mission.

Aid workers from more than 10,000 organisations all over the world have poured into Haiti to help after the devastating January 2010 earthquake.

Writing in the New England Journal of Medicine today, Harvard's Dr John Mekalanos and colleagues said they also confirmed that Haiti's cholera strain carries a mutation associated with more severe disease.

Worst of the worst

"Our genome data puts the Haiti strain in the group that is the worst of the worst," Dr. Mekalanos 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," Dr. Matthew Waldor of Harvard and Brigham and Women's Hospital said.

Haiti's health ministry reports more than 93,000 people have been sickened by cholera since it broke out in Haiti. Haiti had not had a case of cholera in a century, but the ongoing devastation from January's giant earthquake made conditions perfect for its spread.

Cholera strain can circulate for years to come

The US Centres for Disease Control and Prevention said genetic fingerprinting showed Haiti's cholera strain was part of a 49-year-old global pandemic that began in Indonesia and likely was brought to the Caribbean country in a single instance.

The CDC said it was possible the strain could circulate for years in Haiti and the best options were to try to prevent deaths.

When they got some cholera samples from Haiti, the Harvard team contacted Eric Schadt at Pacific Biosciences, which makes a DNA sequencer. They used this $695,000 (about R4.8 million) sequencer to analyse the Haitian cholera's DNA and compared it to strains from elsewhere.

"We definitely linked it to the recent outbreak strains in Bangladesh," Schadt said. But it is not identical, he added, which raises the possibility that the virus may have travelled via elsewhere, perhaps West Africa.

What is clear is that the cholera did not originate locally, Dr Mekalanos said. "Human activity coming from a far-away place brought this strain to Haiti," he said.

Not intending to blame

"Our work is by no way intended to assign blame here," Dr Waldor added. "I do think it is important to understand how cholera likely got to Haiti to see if we can prevent it from happening again."

Many in Haiti have blamed the outbreak on Nepalese United Nations troops stationed near a river that is believed to have been the source of the outbreak. Without a sample from Nepal, however, this would be impossible to prove or disprove, the Harvard team said.

The complete report is available online for free on the New England Journal of Medicine website; a link appears below.

(Reuters Health, Maggie Fox, December 2010)


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