Day 53: Anthrax in America not Columbus’s fault

I really had my eyes opened a couple of years ago, when I happened to be in Tuba City, Arizona on Columbus Day. Tuba City is a very small town on the western portion of the Navajo Nation, and close to the Hopi reservation too. The native kids presumably had the day off of school, like most American children. But they had their own special way of celebrating.

Columbus Day 2007 on the Navajo Nation

And I thought: of course native people don’t like Columbus! He brought pillagers and plunderers, warmongers and disease. 

But, according to new research out of Northern Arizona University in Flagstaff, there’s one bad thing Columbus didn’t do. He almost certainly didn’t bring the nation’s first anthrax.

My former Northern Arizona University grad school classmate, Talima Pearson, shares lead authorship with Leo Kenefic on the new paper, which was published last week in the online journal PLoS ONE. Pearson, Kenefic and their team have used genetic markers to show most of North America’s anthrax came with the first waves of human beings, as they migrated across Beringia during the last ice age.

“We believe this to be an example of an opportunistic human pathogen reflecting ancient human dispersal patterns,” they wrote.

Without the help of people, the anthrax bacteria, Bacillus anthracis, doesn’t get very far. Carried by herd animals like bison, the bacteria tend to kill their hosts quickly. The anthrax spores generally stay in the soil around the carcass. In historic times, humans spread the stuff around when they utilized the carcasses for hair, hide, bones and food.

Past researchers have already documented this mode of anthrax transmission in the Old World, especially along an east-west trade route between Europe and Asia called the “Silk Road.” And now it appears to have happened in the New World, too.

The new study analyzed genetic differences between 387 samples of anthrax recovered from outbreaks across America, including four human cases. The clearest story was revealed by the DNA of the so-called Western North America clade, or grouping, which is well established in central and northern North America. Strains within the clade have cropped up near the Arctic Circle, in Canada, at the U.S. Mexican border and in Haiti. They’ve been linked with 89 percent of non-human anthrax cases across the continent.

Anthrax bacteria prey primarily on herd animals like bison, but people get exposed when they use the animals for hide, fur and food. Credit: Charles M. Kozierok

“Humans appear to have brought B. anthracis to this area from Asia and then moved it further south as an ice-free corridor opened in central Canada” about 13,000 ago, the authors report, adding that the genetics reveal “ancestral populations in northern Canada with progressively derived populations to the south.” The most recent ancestor of the lineage, they say, is in Eurasia.

The study authors found a different genetic story in the separate “Ames” clade that’s been associated with outbreaks in south Texas, and they think the ancestors of those strains were brought more recently — perhaps by trade or colonial animals within the past several hundred years.

“Continent-wide dispersal [of the Western North America clade] likely required movement by later European colonizers,” conclude Pearson, Kenefic and their team, “but the continent’s first inhabitants may have seeded the initial North American populations.”

(You’ll get a little argument about the hypothesis out of Martin Hugh-Jones at Louisiana State University, but you won’t get it from me; Pearson’s a good egg, I’m a fan of NAU, and this is a blog, not a newspaper story, for heaven’s sake.)

Source: PLoS ONE