The intestine of a US cholera victim from the mid-1800s has yielded new clues to the evolution of the deadly bacterium and may help prevent future outbreaks, researchers say.
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 strain.
Results published in The New England Journal of Medicine suggest this strain, which led to five of seven deadly outbreaks in the 1800s, may be more virulent than latter-day counterparts.
Researchers hope their discovery could lead to a better understanding of today's strain of cholera, known as El Tor, which replaced the classical strain in the 1960s and is blamed for recent epidemics.
"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 specimen, from the 1849 pandemic, was in a collection housed at the Mutter Museum, established by the College of Physicians of Philadelphia in 1858.
The World Health Organisation estimates there are up to five million new cholera cases every year, resulting in between 100,000 and 120,000 deaths.
"The genomes of ancestral pathogens that have descendants today reside in these archival medical collections all over the world," Poinar said.