The Haiti cholera epidemic has arisen from a new, South Asian strain carrying three genetic mutations that make it more deadly, and able to spread more aggressively, than previous forms of the disease.
Scientists who sequenced the DNA of the bacterium, which has killed more than 2,000 people, have reported that it is different from Latin America's naturally occurring strain, and over ten times more deadly than a strain that emerged in Peru in 1991.
Two of its three mutations allow the bug to make a 'classical' version of cholera toxin that has not been seen in pandemics for 50 years. The toxin is thought to make the disease more severe than the one that has been spreading around the world since 1961.
The third mutation has equipped the strain to all but replace the one that previously existed in South Asia.
The Haitian cholera strain could displace strains that have circulated in South America since 1991, said Stephen Calderwood of the Massachusetts General Hospital in the United States, co-author of the study.
The bacteria exchange genes with ease so new hybrids, with unpredictable properties, could also arise, he said.
The scientists have supported a call, reported in SciDev.Net last month, for the roll-out of a cholera vaccine, as well as better sanitation in Haiti, to "minimise the spread of the new south Asian strain, and the virulence genes it carries, beyond the shores of this Caribbean island".