In the wake of last year’s earthquake in Haiti, cholera arrived on the island for the first time in 60 years. According to the World Health Organization, 419, 511 Haitians got sick with cholera as of July 31, of which 5,968 died. The infection rate is dropping right now, but the arrival of Hurricane Irene could change that.
As I wrote in December, scientists applied evolutionary biology to find clues to how cholera–or, more precisely, the bacteria Vibrio cholerae— came to Haiti. They compared the DNA in the strain in Haiti to ones that have been found in other parts of the world. From this analysis, they drew a tree, which I’ve reprinted below.
The bacteria in Haiti was more closely related to strains in South Asia than ones from South America. So it was unlikely that cholera came to Haiti floating by water from a nearby country. The evolutionary tree led credence to idea that U.N. peacekeeping troops, some of whom came from Nepal, brought it with them by plane. An outbreak of cholera hit Nepal in September 2010, shortly before a battalion of Nepalese peacekeepers left for Haiti.
This analysis was a bit like a picture taken from 10,000 feet in the air. The bacteria that the scientists analyzed were just a small selection of the many strains that have made people sick over the past few decades. Notably missing from the tree were any bacteria from Nepal. That’s because those strains had not made their way into bacteria collections.
To get a picture up close–and to test the idea that U.N. peacekeepers brought cholera to Haiti–a team of Nepali, American, and Danish researchers collected 24 samples in Nepal at the end of last year. They sequenced the entire genomes of bacteria and compared them to the genomes of Haitian cholera. They reported their results today in the journal mBio.
And here’s their close-up tree. It clearly shows that the Haitian cholera strain evolved from one of four related lineages of V. cholerae circulating today in Nepal. It differs from the Nepalese strain by a single mutation.
It’s amazing that genome-sequencing methods have gotten so powerful that scientists can now use entire genomes to reconstruct an intercontinental outbreak. Yet ten months passed from the outbreak to the publication of this paper. In a blog at the mBio site, co-author Paul Keim explains why: politics. Governments can be reluctant to give up samples that might make them look bad. Building an evolutionary tree of a deadly outbreak takes more than data: it can take a lot of diplomacy, too.
Update: Martin Enserink, writing in Sciencewriting in Science, raises the question of whether the United Nations should compensate Haiti for the outbreak that this study now clearly lays at their doorstep. Hoo boy!
Go Further
Animals
- This ‘saber-toothed’ salmon wasn’t quite what we thoughtThis ‘saber-toothed’ salmon wasn’t quite what we thought
- Why this rhino-zebra friendship makes perfect senseWhy this rhino-zebra friendship makes perfect sense
- When did bioluminescence evolve? It’s older than we thought.When did bioluminescence evolve? It’s older than we thought.
- Soy, skim … spider. Are any of these technically milk?Soy, skim … spider. Are any of these technically milk?
- This pristine piece of the Amazon shows nature’s resilienceThis pristine piece of the Amazon shows nature’s resilience
Environment
- This pristine piece of the Amazon shows nature’s resilienceThis pristine piece of the Amazon shows nature’s resilience
- Listen to 30 years of climate change transformed into haunting musicListen to 30 years of climate change transformed into haunting music
- This ancient society tried to stop El Niño—with child sacrificeThis ancient society tried to stop El Niño—with child sacrifice
- U.S. plans to clean its drinking water. What does that mean?U.S. plans to clean its drinking water. What does that mean?
History & Culture
- Séances at the White House? Why these first ladies turned to the occultSéances at the White House? Why these first ladies turned to the occult
- Gambling is everywhere now. When is that a problem?Gambling is everywhere now. When is that a problem?
- Beauty is pain—at least it was in 17th-century SpainBeauty is pain—at least it was in 17th-century Spain
- The real spies who inspired ‘The Ministry of Ungentlemanly Warfare’The real spies who inspired ‘The Ministry of Ungentlemanly Warfare’
- Heard of Zoroastrianism? The religion still has fervent followersHeard of Zoroastrianism? The religion still has fervent followers
Science
- Here's how astronomers found one of the rarest phenomenons in spaceHere's how astronomers found one of the rarest phenomenons in space
- Not an extrovert or introvert? There’s a word for that.Not an extrovert or introvert? There’s a word for that.
- NASA has a plan to clean up space junk—but is going green enough?NASA has a plan to clean up space junk—but is going green enough?
- Soy, skim … spider. Are any of these technically milk?Soy, skim … spider. Are any of these technically milk?
- Can aspirin help protect against colorectal cancers?Can aspirin help protect against colorectal cancers?
Travel
- What it's like to hike the Camino del Mayab in MexicoWhat it's like to hike the Camino del Mayab in Mexico
- Is this small English town Yorkshire's culinary capital?Is this small English town Yorkshire's culinary capital?
- Follow in the footsteps of Robin Hood in Sherwood ForestFollow in the footsteps of Robin Hood in Sherwood Forest
- This chef is taking Indian cuisine in a bold new directionThis chef is taking Indian cuisine in a bold new direction