A look back at western Canada in the 18th and 19th centuries has shed light on the behavior of tuberculosis, one of the world’s deadliest diseases. Researchers here studied the travels of a strain of disease that spread to the indigenous peoples from French Canadian voyageurs during the fur trade era, and:
"We found there was this widespread, low-level dispersal of tuberculosis that did not become obvious until environmental changes occurred that created conditions conducive to epidemics," said Caitlin Pepperell, MD, an infectious diseases specialist at Stanford.
Indeed, the disease started to spread as early as 1710, but it wasn't until the late 1800s that an epidemic broke out:
The process, [Pepperell] said, resembles the way a smoldering fire can spread underground, through the roots of trees and brush, then burst into fire without warning.
"Tuberculosis epidemics are the outcomes of a process that has effectively been occurring underground," she said - unlike smallpox, which quickly escalates into epidemics.
"This helps explain why it has been so extraordinarily difficult to eradicate TB."
The study appears in Proceedings of the National Academy of Sciences.