Canadian lab cracks the DNA code for 1800’s cholera pandemic

At Hamilton, Ontario’s McMaster University, scientists have once again travelled back in time to solve a medical mystery.

Known as the Ancient DNA Centre at the university’s Department of Anthropology, it has become a leader in the emerging field of paleopathogenomics, the excavation of the genetic sequences of pathogens that infected in eras before science could detect and identify them.

Recently the researchers,with collaboration from American colleagues, mapped the genetic blueprint of the bacteria from a postage stamp sized piece from the preserved intestine of a man in Philadelphia who died of the disease in 1849.

 The research confirms that this second pandemic, of the seven world-wide outbreaks in the past 200 years, was caused by what is known as the “classical” strain of Vibrio cholera. Most cholera since the 1960’s has been caused by another strain, El Tor.

 The research has been published this month in the New England Journal of Medicine.

“It’s fantastic to be able to actually study the evolution of these pathogens in real time,” said Hendrik Poinar, director of the Ancient DNA Centre and senior author of the paper.

He said the mapping process will help in understanding how diseases evolve and also aid in developing drugs to combat such pathogens.

 The Ancient DNA Centre had earlier cracked the genetic code for the plague. Using teeth recovered from the skeletons of a mass grave in London, they sequenced the blueprint for Yesinia Pestis-also known as the Black Death- and responsible for the pandemic which wiped out 60% of the population of Europe in the mid-thirteenth century.

The difficulty with cholera however is that unlike the plague and other pandemics which leave traces in bones, teeth and even hair follicles, it is only found in gastrointestinal tissue.  Such tissue decays rapidly and digging up the body of someone who died in the 1800’s pandemic would not provide intestinal organs.

Dr Poinar remembered another source however, the tissues collected in jars of preservative in medical museums, hospitals, and universities around the world.

One such collection is held at Philadelphia’s Mutter Museum, established by the College of Physicians of Philadelphia in 1858. It had several preserved intestines from people thought to have died during the second of the cholera pandemics, which dated from 1829 to 1849.

 The museum agreed to let the researchers have small pieces of three, which all tested positive for cholera. The DNA sequence was recovered from one.

The genetic blueprint shows the classical strain is missing some genetic material present in the modern El Tor strain and perhaps explains why this classical strain began to wane in the 20^th century.

 The work was funded by the Natural Sciences and Engineering Research Council, the Social Sciences and Humanities Research Council, an NHMRC Australia Fellowship and an Ontario Graduate Scholarship