The cholera epidemic that has killed 2,120 people and hospitalized 44,000 in Haiti probably was carried there by people who brought it from South Asia, according to an analysis of the bacteria’s genome.
Using tissue samples from patients in Haiti, scientists at Menlo Park-based Pacific Biosciences of California Inc. took only two days to map the pathogen’s genome, the set of genes that makes any organism unique. The Haitian strain is almost identical to types found in South Asia and differs greatly from those circulating in nearby Latin America, according to the analysis published today in the New England Journal of Medicine.
This suggests humans carried the Asian strain into the country, which hadn’t had a cholera outbreak in more than 100 years even with its desperate poverty and lack of sanitation, said Matthew Waldor, an author of the study. Better screening is needed of people traveling from areas with endemic cholera to regions where conditions could lead to an outbreak, he said.
“This strongly argues that cholera was introduced to Haiti not on an ocean current from Latin America but by human activities,” said Waldor, an infectious disease specialist at Harvard Medical School in Boston. “It also suggests we can prevent future Haitis by altering some policies.”
Cholera, which triggers severe diarrhea and dehydration and can cause rapid death, is caused by various strains of the bacterium Vibrio cholerae and is usually transmitted in contaminated water.
The analysis also suggests that the Asian strain that hit Haiti is especially virulent and raises the risk that it may supplant other strains circulating in Latin America and spread there, Waldor said. There is a need to increase the production of cholera vaccines, which are now in short supply, he said.
After the Haitian earthquake in January, the U.S. Centers for Disease Control and Prevention concluded that even with the extensive damage to the country’s poor sanitation system, there was not a great risk of a cholera outbreak because the disease hadn’t been seen there in so long, Waldor said.
“That was wrong,” he said. “They didn’t consider global movement of human beings.”
As a public health measure, people who travel from areas that have high cholera rates should be screened before traveling to regions where conditions could allow an epidemic to spread rapidly, he said.
Rioting at Bases
Speculation that cholera may have been brought to the country by Nepalese soldiers who came to the island as part of a United Nations peacekeeping force has led to rioting at bases where the peacekeepers are stationed. UN officials said Dec. 7 they are evaluating a report by a French epidemiologist who concluded the outbreak began at a camp for the Nepalese peacekeepers.
The new genomic findings are consistent with a Nepalese origin, though the data don’t prove it, Waldor said.
The ability of researchers to sequence the genomes of the cholera strains in just two days is due to advances in technology developed by Pacific Biosciences, said the company’s chief scientific officer, Eric Schadt, one of the authors of the study. The cost of chemicals used was less than $500 for each genome they sequenced, he said.
Scientists have been trying to get the cost of sequencing a human genome to $1,000 or less. While the cost continues to drop, the $1,000 human genome is not yet here, Schadt said. Human genomes are about 1,000 times larger than that of cholera bacteria.