Housing was also of low quality, with too many people living in close quarters, often lacking adequate ventilation or protection against the elements.
"With tuberculosis, even such simple things as having windows that open can actually make quite a large difference in terms of the risk of transmission," Pepperell said. "Any situation where there is poor ventilation, it is dark and it is crowded is perfect for transmitting TB."
Pepperell, a physician and an instructor in the division of infectious diseases at Stanford's School of Medicine, is the lead author of a paper about the study published online by Proceedings of the National Academy of Sciences this week.
"Up to now, it has been relatively hard to define the locations of origin of a strain of tuberculosis more precisely than a continent," said Marcus Feldman, professor of biology and a co-author of the paper. By looking at large numbers of bacterial samples and integrating genetic analysis with the work of fur trade historians, the researchers gained insight into how this particular strain must have spread.
They worked with archived M. tuberculosis bacterial samples from indigenous communities across Alberta, Saskatchewan and Ontario that had been previously collected by provincial health authorities. All the analyses were done on bacteria, not people. The scientists found a single strain of tuberculosis, characterized by a specific mutation, dominated in every community.
Earlier research had established that the same strain was also dominant among French Canadian residents of Quebec.
"The tuberculosis strains from Quebec are missing a specific piece of DNA; that's how you can track them back to Quebec," Feldman said.
Tuberculosis can only be
|Contact: Louis Bergeron|