Researchers on the track of ancient anthrax

Researchers have been tracking the arrival of anthrax to North America, and indications are that the trail is at least 13,000 years old—many millennia before European colonists brought their own set of diseases to the New World.

In fact, researchers believe, animals and indigenous populations may have tracked disease to North America by way of Beringia, the land bridge between Siberia and Alaska that today is mainly covered by the shallow Bering Sea.

Paul Keim

Led by Northern Arizona University Regent’s professor Paul Keim and NAU professor emeritus Jim I. Mead, now professor and chair of geosciences at East Tennessee State University, the researchers have molecular data that indicate the presence of North American anthrax far earlier than anyone had previously believed.

“The dispersal of anthrax throughout the continent required relatively recent movement by European colonizers,” Keim said. “But the continent’s first human inhabitants may have seeded the initial North American anthrax populations in the far north.”

Keim, who also is director of the Pathogen Genomics Division for the Translational Genomics Research Institute in Phoenix, explained that high resolution genomic analysis coupled with extensive strain collections enhanced the team’s ability to reconstruct ancient epidemiological occurrences.

Mead said that during the last Ice Age—more than 14,000 or so years ago—inhabitants could walk from Siberia over to Alaska but then would be confronted with a wall of ice from northern Alaska south to about Seattle.

Jim Mead

“This continental ice sheet barrier kept Beringian plants and animals up north and west, while south of the ice (about where the Canadian and U.S. border are today) were different biological communities,” he said. “It appears from the molecular data that anthrax was not south of the ice barrier.”

About 14,000 years ago the ice barrier melted enough to create a corridor between Beringia and the continental United States.

“At some point anthrax appears to have steadily moved south into what is now the United States,” he said. “This corridor would have permitted some species to continually move south—nothing was stopping them. Various animals apparently did this dispersal—bison being one of them and humans another.”

Disease introduction into the New World during European colonial expansion is well documented and had a major impact on indigenous populations, Keim explained. “However, few diseases have been associated with early human migrations into North America.”

Bacillus anthracis—the bacterium that causes anthrax—has dispersed globally through commerce and trade of animal products contaminated with B. anthracis spores, according to Keim.

Without human involvement, infected animals typically die within seven to 10 days, seeding only the surrounding soil with spores and keeping the spread of the disease relatively contained. The potential for dispersion even among migratory herds is limited since infected animals typically die quickly before extensive dispersal can occur.

Historically, an animal that died of anthrax was scavenged by people for its hair, hide, and bones and was even consumed, helping the dispersal of spores well away from a carcass.

Imported spore-contaminated animal hides account for many of the recent U.S. human anthrax cases, though such modern cases rarely result in dispersal.

“With the exception of the most recent human cases, the current distribution of B. anthracis can be traced to historical human dispersion, trade and migratory patterns,” Keim said.

Anthrax is a potentially fatal disease caused by the bacterium Bacillus anthracis. It usually develops in livestock and is relatively rare in humans, unless deliberately spread.

Some scholars believe the fifth and sixth biblical plagues of Egypt told in Exodus were anthrax caused.

Keim is one of the investigators who linked the 2001 anthrax-letter attacks that killed five people and sickened 17 to the U.S. Army Medical Research Institute for Infectious Diseases in Frederick, Md.

Bruce Ivins, an Army researcher, committed suicide in 2008 as federal agents were preparing to charge him with carrying out the attacks.

In addition to Keim and Mead, the research team includes Leo J. KeneficTalima PearsonJames M. Schupp,Wai-Kwan Chung, Jodi A. Beaudry, all of Keim’s Center for Microbial Genetics and Genomics; David Wagner, NAU assistant professor of biological sciences; Jacque Ravel, from the Institute for Genome Sciences, University of Maryland School of Medicine; Alex R. Hoffmasters, of the Bacterial Zoonoses Branch, Centers for Disease Control and Prevention in Atlanta.

Mead now believes the next step is to travel to Siberia to “find frozen critters” that may indicate anthrax. “It wasn’t just bison carrying anthrax; it was people and other animals,” he said. “We now need to go back into the Ice Age.