McMaster scientists unlock cholera's secrets

A team of McMaster scientists is enjoying a great start to the new year after solving a genetic code related to an historical cholera outbreak. The team was able to determine the cholera bacteria that caused a widespread outbreak of the diarrheal disease in the 19th century.

The researchers from McMaster’s Ancient DNA Centre reconstructed the entire Vibrio cholerae genome using a piece of tissue from the intestine of a Philadelphia man, which had been remarkably preserved by Philadelphia’s Mütter Museum.

Findings from the study were published in the New England Journal of Medicine on Jan. 8, helping to pin down the cause of the earliest forms of the infectious disease in India, Europe and North America.

Before they could begin the laborious process of reconstructing the complex genome, the research team had to locate a well-preserved specimen with remnants of the disease. This was no easy task as the pathogen only colonizes the intestines: normally the first internal organ to decompose after death.

Doubts as to whether finding a specimen was possible were alleviated when Hendrik Poinar, Associate Professor and Canada Research Chair within the Department of Anthropology and Principal Investigator at the Ancient DNA Centre, learned that the Philidelphia’s Mütter Museum had preserved internal specimens from alleged cholera victims from its curator, Anna Dhody.

Graduate student Alison Devault was at the helm for much of the lab work as part of her PhD thesis and said that she was unsure whether an analysis of the specimen would reveal it to be imbued with cholera DNA.

“Oftentimes in ancient DNA work you can have a very promising sample, but because of poor conditions for DNA preservation — such as fluctuating temperatures or bacterial or chemical changes that overly degrade the DNA — you are disappointed.”

Devault said her peers also entertained doubts that the alleged cholera victims were just that and nothing more.

“There was always another possibility, that the alleged cholera victims did not actually have cholera at all, or the historical disease we believed to be cholera was actually due to some completely different pathogen.”

The study revealed the cholera that the man suffered from to be of the classical strain, once the prominent form of epidemic cholera.

Although a strain called El Tor replaced the classical as the main pathogenic form of the disease in the 20 century, Devault says studies of its predecessor can be crucial to our understanding of a disease which infected 3 to 4 million people in 2012, killing 100,000.

“We know from historic accounts and records that 19th century cholera was extremely widespread and devastating on a global scale. Although it is still unclear exactly why that was the case, having full-scale genome information from a 19th century strain is one great starting point for future research,” she said.

Devault hopes that additional rare specimens can be found for study. This would allow further insight into how cholera has evolved over time and perhaps lead to better preventative measures to be established.