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.

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Two officers shot in Louisville amid Breonna Taylor protests

Police officers stand guard during a protest in Louisville, Kentucky. Photo: Ben Hendren/Anadolu Agency via Getty Images

Louisville Metro Police Department said two officers were shot downtown in the Kentucky city late Wednesday, just hours after a grand jury announced an indictment in the Breonna Taylor case.

Driving the news: Metrosafe, the city's emergency services, said it received reports of a shooting at South Brook St. and Broadway Ave., near the area where protests were taking place. A police spokesperson told a press briefing the injuries of both officers were not life-threatening. One officer was "alert and stable" and the other was undergoing surgery, he said.

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Coronavirus dashboard

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  1. Global: Total confirmed cases as of 9 p.m. ET: 31,778,331 — Total deaths: 974,436 — Total recoveries: 21,876,025Map.
  2. U.S.: Total confirmed cases as of 9 p.m. ET: 6,943,078 — Total deaths: 201,930 — Total recoveries: 2,670,256 — Total tests: 97,459,742Map.
  3. Health: CDC director says over 90% of Americans have not yet been exposed to coronavirus — Supply shortages continue to plague testing.
  4. Politics: Missouri Gov. Mike Parson tests positive for coronavirus — Poll says 51% of Republicans trust Trump on coronavirus more than the CDC.
  5. Technology: The tech solutions of 2020 may be sapping our resolve to beat the coronavirus
  6. Vaccines: Johnson & Johnson begins large phase 3 trial — The FDA plans to toughen standards.
  7. Sports: Less travel is causing the NBA to see better basketball.
  8. Future: America's halfway coronavirus response

Biden: Breonna Taylor indictment "does not answer" call for justice

Former Vice President Joe Biden. Photo: Leigh Vogel/Getty Images

Former Vice President Joe Biden on Wednesday condemned the grand jury indictment of a Louisville police officer who entered Breonna Taylor's home in March in a botched drug raid that led to her death, saying in a statement the decision "does not answer" for equal justice.

The big picture: Biden called for reforms to address police use of force and no-knock warrants, while demanding a ban on chokeholds. He added that people "have a right to peacefully protest, but violence is never acceptable."

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