Nepalese troops brought cholera to Haiti with earthquake relief
The United Nations sent Nepalese peacekeeping troops to bring relief to Haiti amid devastation from a 7.0-magnitude earthquake in 2010. A new study concludes that the peacekeepers brought something else too: cholera, triggering an epidemic that has sickened hundreds of thousands of Haitians and killed more than 8,000.
After sequencing the DNA of 23 samples of the cholera-causing bacterium from Haiti and comparing them to the DNA of strains found elsewhere, researchers said the outbreak could be traced to Nepal, where the disease is endemic.
They also concluded that the outbreak in Haiti came from a single source, undermining the hypothesis that the disease was repeatedly introduced to the nation over the last three years.
Cholera is caused by a bacterium called Vibrio cholerae. It is typically spread through contaminated food or water, causing symptoms like diarrhea, vomiting and dehydration. Treatments include oral rehydration salts, intravenous fluids and antibiotics.
The World Health Organization estimates that 3 million to 5 million people contract cholera annually, causing 100,000 to 120,000 deaths each year.
The disease spreads quickly in areas with inadequately treated sewage and drinking water, as is often the case after a natural disaster.
Cholera emerged in Haiti about nine months after the January 2010 quake that killed hundreds of thousands. The outbreak was a surprise because the disease had never been documented in the small island nation.
At first, circumstantial evidence reported by French epidemiologist Renaud Piarroux indicated that poor sanitary conditions at a United Nations camp about 40 miles outside the capital of Port-au-Prince resulted in contamination of local water supplies. That didn't explain how V. cholerae wound up in the camp in the first place.
About 1,300 Nepalese peacekeepers arrived in Haiti in October 2010 to help with earthquake recovery efforts. The first indication that they might be responsible for the cholera outbreak was a December 2010 study that used DNA sequencing to determine that the bacterial strain most likely came to Haiti from South Asia, not from Latin America.
Another study in 2011 found that V. cholerae samples from Haiti were almost genetically indistinguishable from Nepalese samples. Yet some people remained unconvinced because most of the samples analyzed came from Nepal.
The study published last week in mBio, the journal of the American Society for Microbiology, considered more than 100 samples from recent cholera outbreaks in 16 countries. Even with more candidates in the mix, the Haiti and Nepal samples were strikingly similar, perched on the same branch of the evolutionary tree that researchers constructed with their data.
“They're very closely related,” said William Hanage, a study author and infectious disease expert at Harvard University's School of Public Health.