Columbus innocent over anthrax in the Americas

Columbus took a lot of things to the New World but anthrax wasn't one of them

When Europeans invaded the Americas they introduced many Old World diseases that decimated Native Americans. Scientists had thought that anthrax was one of them. New research shows, however, that the deadly bacteria arrived in the Americas thousands of years earlier, when Stone Age humans crossed the Bering land bridge.

The military Ames strain behind the 2001 anthrax attacks, however, is a recent Asian immigrant.

Anthrax bacteria can live in soil for decades as tough spores, until they are inhaled by a grazing animal. Then they multiply explosively, kill the animal, and bleed into the soil to await the next victim.

The disease was a scourge of cows, cowboys and settlers in the Wild West: spores still mark the route of the Chisholm Trail and other cattle drives. It is only since the intense genetic analysis of anthrax that followed the 2001 attacks, though, that enough has been known about the bug to trace its family tree in the Americas.

Early invader

Anthrax initially evolved in southern Africa, earlier work has demonstrated. Paul Keim of the Northern Arizona University, who led the genetic investigation of the attacks, says that normally anthrax spores do not move far from their dead victims, so it was probably humans carrying scavenged, spore-infested hair and hides who moved one anthrax "family" into northern Africa, then across Eurasia.

That transfer then continued, Keim says. His new work confirms previous studies suggesting that many strains of American anthrax came on European wool and cattle in recent centuries. The Ames strain used in the anthrax attacks, for example, naturally occurs only in Texas, but differs from Eurasian anthrax by only about eight mutations, showing it is a recent immigrant.

But the analysis also shows that most of the anthrax lurking in the grasslands from northern Canada to Mexico differs by up to 106 mutations, showing it branched off from the Eurasian form long ago – roughly when humans and animals entered the Americas from Siberia then moved south as grasslands opened up in central Canada around 13,000 years ago. .

Mammal extinctions?

"The line of descent shows a clear gradient from north to south," Keim says. Moreover the family tree shows one introduced ancestor gave rise to all the more recent members of the family. The fact it moved from north to south shows it was carried by the invading humans, not animals moving back north as the glaciers retreated.

For anthrax, at least, Columbus is off the hook. But the finding may also have implications for the extinction of many American mammals shortly after humans arrived.