Nov 10, 2017

The human story of cholera started in Asia

Cholera patients in a clinic in Harare, Zimbabwe, in January 2009. Photo: Tsvangirayi Mukwazhi / AP

The planet is in the midst of its seventh cholera pandemic — one that affects about 3 million people each year and, unlike past pandemics that faded away, persists. Stopping its spread hinges on tracking its movements.

By analyzing the genomes of bacteria isolated from samples collected during cholera outbreaks over the past half-century, scientists have now determined that outbreaks in Africa and the Americas were sparked by strains that arrived from Asia. Tracing the paths into and around these regions offers new targets for efforts to control the disease.

The back story: The seventh pandemic began in Indonesia in 1961, then spread to South Asia (1963), Africa (1970), Latin America (1991) and then Haiti (2010). A current outbreak in Yemen just surpassed that in Haiti, and is nearing 1 million cases in the war-torn country.

The challenge: "When cholera was imported into Africa in 1970, it was easy to spot introduction routes and propagation routes because it was a new disease. At some point, the signal was lost because it was everywhere and you weren't able to link the outbreaks to each other," says Francois-Xavier Weill from the Institut Pasteur in Paris, who was involved in both studies.

The bacteria responsible for cholera, Vibrio cholerae, doesn't change much over time, so differences in the DNA of one strain compared to another are hard to spot. So the researchers turned to whole genome sequencing to analyze 714 samples collected on the three continents.

What they found: In Africa, cholera epidemics were traced to at least 11 different introductions from Asia since 1970. (The last five were multi-drug resistant strains.) And, it tended to enter through East/Southern Africa and West Africa.

"All the action should be taken there first," Weill says of public health surveillance efforts. Knowing the genetic fingerprint of the pandemic-producing strain could also inform decisions about when and where to use a global stockpile of cholera vaccine.

The researchers also found that one strain caused an outbreak in Africa that lasted 28 years. Both papers indicate that there's no local reservoir for cholera, meaning if a strain disappears at some point and another isn't introduced, cholera could be eliminated from the region, says Weill.

What's next: Until now, models of cholera's pathways were based on tens of samples. "Not only does the analysis provide more insight into how cholera moves but it also adds samples for others to make inferences so more researchers will be able to study its movement," says Andrew Azman from Johns Hopkins University, who was not involved in the research but studies cholera's epidemiology in East Africa. He says by adding the whole genome sequences of hundreds of strains to the public domain researchers can further understand the dynamics of how cholera is transmitted. Azman plans to pair Weill's results with detailed analysis of cases of cholera in Africa.

Go deeper

Sign of the times: A pro-Warren super PAC

Democratic presidential candidate Sen. Elizabeth Warren at a rally in Nevada. Photo: Alex Wong/Getty Images

A group of women progressives who back Sen. Elizabeth Warren has formed Persist PAC, a super PAC airing pro-Warren ads starting Wednesday in an effort to boost her performance ahead of Saturday's crucial Nevada caucuses, a spokesman told Axios.

Why it matters: Warren has spoken adamantly against the influence of unlimited spending and dark money in politics. But these supporters have concluded that before Warren can reform the system, she must win under the rules that exist — and that whether she likes it or not, their uncoordinated help may be needed to keep her viable through this weekend's contest and into South Carolina and Super Tuesday.

Go deeperArrowUpdated 56 mins ago - Politics & Policy

Pentagon policy chief resigns amid reported discord with Trump

John Rood. Photo: Mark Wilson/Getty Images

John Rood, the Pentagon's top policy official, will resign from his post at the end of the month, CNN first reported and President Trump confirmed.

The state of play: CNN said Rood "was perceived as not embracing some of the changes in policy the White House and senior Pentagon officials wanted," such as peace talks in Afghanistan with the Taliban and a decision to cut back on military exercises with South Korea as the president courted North Korea's Kim Jong-un.

Coronavirus cases rise, as warnings of global pandemic grow

Data: The Center for Systems Science and Engineering at Johns Hopkins, the CDC, and China's NHC; Note: China refers to mainland China and the Diamond Princess is the cruise ship offshore Yokohama, Japan. Map: Danielle Alberti/Axios

We may be "at the brink" of a global pandemic, warns a top U.S. public health official, as cases continue to spread despite containment efforts. Meanwhile, the global economy is being affected, including the tech manufacturing industry.

The big picture: COVID-19 has now killed more than 2,000 people and infected over 75,000 others, mostly in mainland China, where the National Health Commission announced 136 new deaths since Tuesday.

Go deeperArrowUpdated 2 hours ago - Health