In the summer of 1849 a mass epidemic of cholera invades the City of London, leaving more than 13,000 dead. It was not the first or the last to terrorize the city before the disease disappeared in 101; major outbreaks occurred in 1832, 1854 and 1866. Now, new evidence suggests that the epidemic in 1849, and two of the worst epidemics of the city, may have come with a warning-a prequel that could alert authorities health epidemics pending today.
These prequels, called herald wave, killed hundreds, not thousands, said Joseph Tien, a mathematical biologist at Ohio State University in Columbus. His team detected three of them-each happening months before one of the four "major" cholera years in London.
It was the season that gave them away. Tien and his colleagues examined the records of weekly cholera deaths in London stretching 1824-101, when the last death from cholera recorded in the city. They found that cholera outbreaks ever been hit, with only three exceptions: spring 1832, autumn 1848 and winter 1853. All three thugs homes was followed by a particularly severe outbreak that summer
"They kind of jumped from the cholera data," said Tien, whose team publishes its results online today in Royal Society Interface . Researchers believe that the invasion of a new cholera strain could trigger prequels. A new bacterium could do damage to a vulnerable population not immune, but if it happened during the off-season, the weather does keep it in check. That is, until the summer, when warmer temperatures could allow it to resurface with a vengeance. A mathematical simulation confirms this idea, but the authors admit that the new strain hypothesis needs to genetic or biological data to back up the
One potential key in the event of the team took place in 1866 :. A cholera epidemic that has killed more than 5,000 people and came with no apparent herald wave. The researchers suggest that this could be a new strain happened to arrive just as the cholera season began. But Tien recognizes other environmental factors might also be involved.
"I'm impressed and a little excited about this product," says Donald Olson, an epidemiologist at the International Society for Disease Surveillance Boston who was not involved in the research. Olson has studied a wave similar to herald the 1918 influenza epidemic in New York City, part of the great "Spanish flu", but he said that this is the first time someone recorded for cholera.
Justin Lessler, an epidemiologist at Johns Hopkins University in Baltimore, Maryland, agrees that this would be a first. But Lessler said not be surprised that cholera outbreaks could preludes. "people who do modeling expect this for all seasons based epidemic."
the biggest challenge, according Lessler, is to find where the cholera season occurs in various places. In temperate climates, such as London that it says it is reasonable to expect the strike of cholera in the hot summer months. But in the tropics, such as Bangladesh, one of the key strongholds of cholera in the 21st century, the disease may depend more on local factors such as the timing of the rainy season. And Haiti, where cholera has not been seen for at least a century, it is even less clear when the season begins. Because the Haitian population has virtually no immunity, cholera could be devastating no matter when it hit.
However, for regions where researchers know the season when cholera usually occurs Lessler said an epidemic out of season could be an invaluable warning to prepare for more serious in the near future. "You do not want to be too happy when this off-season epidemic started declining."
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