The intestine of an American cholera victim from the mid-1800s has yielded new clues to the evolution of the deadly bacterium and may help prevent future outbreaks, researchers said.
Using the sample of an intestine, preserved in a jar at a Philadelphia medical museum, scientists reconstructed for the first time the genome of classical cholera, the predecessor of the modern-day strain.
Results published in The New England Journal of Medicine suggest this strain, behind five of seven deadly outbreaks in the 1800s, may be more virulent than its contemporary counterpart.
Researchers said they hope their discovery could lead to a better understanding of today's strain of cholera which replaced the classical strain in the 1960s and is blamed for recent epidemics like Haiti.
"Understanding the evolution of an infectious disease has tremendous potential for understanding its epidemiology, how it changes over time and what events play a role in its jump into humans," said evolutionary geneticist Hendrik Poinar, associate professor and director of the McMaster University Ancient DNA Centre.
The preserved organ was crucial to the effort, since DNA from cholera resides only in soft tissues and cannot be detected in bone.
The type of cholera behind most of the 1800s outbreaks is believed to have originated in the Bay of Bengal off India.
The specimen was part of a collection housed at the Mutter Museum, established by the College of Physicians of Philadelphia in 1858, after the city was devastated by cholera earlier in the century.
The intestine came from a male victim of the 1849 pandemic.
The World Health Organisation estimates there are three to five million new cholera cases every year, causing between 100,000 to 120,000 deaths.
"The genomes of ancestral pathogens that have descendants today reside in these archival medical collections all over the world," said Mr Poinar.
"We have access to hundreds of thousands of ancient specimens, which hold tremendous potential to determine the origins of past epidemics."