Patience may be a virtue in a person, but in an infectious disease, it is insidious. Witness tuberculosis, which can lie dormant in a human host for decades before bursting forth into infection. TB's stealthy nature has made it difficult to decipher how it spreads, seriously hampering efforts to control it. The World Health Organization estimates that a third of the people on Earth are infected.
Now, a study led by Stanford scientists has provided new insights into the behavior of tuberculosis by tracing the travels of a particular strain of the disease that was unintentionally spread among the indigenous peoples of western Canada by French Canadian voyageurs during the fur trade era. Although the disease was probably brought into the native populations repeatedly from about 1710 to 1870, it didn't spark an epidemic until the fur trade had largely ended, more than 150 years from when it was first introduced.
"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, an infectious diseases specialist at Stanford.
The process, she 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 conditions that finally triggered epidemics in Canada in the late 1800s likely resulted from the relocation of native peoples onto reservations, where health conditions were often abysmal.
The biggest factor, she said, was probably malnutrition. The buffalo, once a dietary mainstay of indigenous peoples on the prairie, had been v
|Contact: Louis Bergeron|