DNA shows history of TB spread

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PALO ALTO, Calif., April 4 (UPI) -- Indigenous peoples doing business with fur traders in Canada in the 18th century contracted tuberculosis in the bargain, researchers said.

Infectious disease specialist Caitlin Pepperell of Stanford University studying the DNA profile of a tuberculosis strain collected from a French Canadian population compared it to one in native communities and found the TB strains had very similar genetic signatures, AAAS ScienceMag.org reported Monday.

Pepperell and her colleagues traced the spread of a certain strain of tuberculosis, characterized by a unique patch of missing DNA, to a period in the 18th century when French fur traders moved into Canada and married indigenous women, bringing TB with them.

The disease endured in native communities "at a low, grumbling level" for several decades because otherwise healthy people can live for decades with TB infections without becoming sick, Pepperell said.

When hide hunters nearly exterminated the buffalo native populations depended on, and settlers banished the native peoples to reservations, the disease exploded into large-scale epidemics in the 19th and 20th centuries, the researchers said.

The central message of the finding, Pepperell said, is that TB can spread widely and persist at almost unnoticeable levels until stressful conditions, such as crowding or poor nutrition, weaken human hosts and give the bacteria a leg up.

The finding highlights the tenacity of the disease, she said, by showing how it can hide undetected in small populations for long periods of time.

"We have thrown a lot of resources at TB, but it has really hung on," she said.