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Unlike MERS, whooping cough spreads rapidly from person to person. As a result, there are millions of cases around the world every year. NPR's Richard Harris reports on the surprising origin of that potentially deadly disease.
RICHARD HARRIS, BYLINE: Whooping cough is caused by a bacterium called bordetella pertussis. It was a leading cause of childhood death until a vaccine was developed for it and now scientists have unraveled the story of how it emerged to begin with. Julian Parkhill at the Sanger Institute in Cambridge, England, is part of large team that looked at hundreds of samples of pertussis from all around the world to create a pertussis family tree.
JULIAN PARKHILL: It's very much like doing a genealogical study and saying that you identified my great-great-grandfather, who lived between these dates.
HARRIS: In this case, the scientists discovered the ancestor of modern-day pertussis emerged suddenly and quite recently in terms of human history just in the 15th or 16th centuries.
PARKHILL: That isn't very long ago and really, that was quite a surprise.
HARRIS: It is consistent, though, with historical documents. The distinctive cough with its whooping sound was mentioned in a 15th century Korean medical text The first documented epidemic arose in Paris in the year 1578. Before that, there was no sign of such a distinctive disease.
PARKHILL: It's not mentioned in any of the Ancient Greek or any of the Egyptian records, or anything like that.
HARRIS: Parkhill says a close reading of the genes also provides clues about where the human disease came from.
PARKHILL: It appears to have evolved from a single event, and that event was the adaptation to the human population.
HARRIS: It seems that a closely-related bacterium, found in all sorts of animals including dogs and rabbit, mutated. That change turned it into one that spreads easily from person to person and causes that agonizing cough. The study published online in the journal MBIO, also has implications for controlling the disease today.
The bacterium continues to evolve, and one consequence is the current vaccine isn't as effective as it used to be. Parkhill says it's time to use this new genetic information to tune up the vaccine.
PARKHILL: We're used to this in other organisms. For influenza we come out with a new vaccine every year or two.
HARRIS: The current vaccine has been highly successful. Though there have been a few notable outbreaks, the CDC estimates that the vaccine has prevented 50 million cases of pertussis in the United States since 1994. Richard Harris, NPR News.
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