Tracing anthrax's American roots

— -- Anthrax, the bioterror scourge and cattle killer, has a surprisingly ancient North American pedigree, report genetic researchers.

Best-known as the lethal bacteria mailed in the 2001 bioterror attacks that killed five people, anthrax is found naturally in the soil worldwide. Cows and goats — grazing animals — most often suffer from anthrax, with veterinary cases reported every year.

"With genomic analysis, we can really ask interesting questions about the origins of something like anthrax," says Talima Pearson of Northern Arizona University in Flagstaff, an author of a PloS ONE journal study that sought the hardy bug's origins. The introduction of cattle by Spaniards, and trade with Europe that started in the 1600s have often been pointed to as the start of the disease in North America, part of a wave of Old World diseases, such as the smallpox thought to have killed millions in the colonial era.

Call it a case of archaeology by biology. In the study, Pearson and colleagues looked at 285 anthrax-laced soil samples from throughout Canada and the United States. As an outgrowth of the 2001 terror attacks, the NAU lab has expanded its "molecular genotyping" capabilities for the bacteria, and looked at 2,850 gene markers common to all those samples to see how closely related each one was, and how those links changed with geography.

The researchers developed a "molecular clock" to estimate the age of the bacteria samples. Anthrax reproduces by cloning itself, so changes to its genes are relatively rare, says NAU study senior author Paul Keim, which suggested to the researchers that they should estimate its age based on the frequency of those changes.

Along the lines of the conquistador theory, the team expected to see the oldest varieties of Western North American anthrax residing in the south and diversifying as they moved northwards. Instead, says the study, the analysis found the oldest, "ancestral" bacteria populations in northern Canada, with newer ones further south."The pattern just jumped out for anthrax coinciding with the peopling of the New World," says geologist James Mead of East Tennessee State University in Johnson City, a study co-author, after the molecular clock roughly traced the oldest, northernmost, samples to around 13,000 years ago.