March 16, 2009

Anthrax’s Movement Throughout History

Scientists are suggesting that the deadly bacteria anthrax has ancient links to North America.

Anthrax was widely publicized during the attacks of 2001, in which envelopes laced with the deadly bacteria were linked to the deaths of five people. Since those attacks, US agencies have spent more than $50 billion on defenses against biological warfare although no new anthrax attacks have been reported.

The bacteria's effects are more commonly seen among grazing animals. According to USA Today, veterinarians report cases of anthrax in animals every year.

"The dispersal of Bacillus anthracis, Yersinia pestis, and human RNA viruses often reflect short term human movement frequently associated with trading contaminated animal products or inadvertently transporting primary vectors or hosts," researchers wrote in the journal PloS One.

"The history of B. anthracis in North America has certainly been affected by recent trade, and livestock movement, however here we present evidence that the introduction of this pathogen can be traced to much more ancient human migrations. We believe this to be an example of an opportunistic human pathogen reflecting ancient human dispersal patterns."

Researchers analyzed 285 samples of soil which contained anthrax from the US and Canada. The molecular genotyping capabilities used by researcher Talima Pearson and colleagues of North Arizona University in Flagstaff have been greatly improved as a result of the 2001 terror attacks, according to USA Today.

Anthrax has been previously considered to have been carried by the introduction of cattle by Spanish conquistadors in the 1600s.

"In North America, two distinct types of anthrax cases are seen. Many have been observed along the East Coast and are associated with trade and industrial processing of contaminated animal products, often wool in textile mills," Pearson and colleagues wrote. "These cases contribute to the overall genetic diversity of North American B. anthracis isolates, but generally represent small case clusters that do not become ecologically founded."

"In contrast, western North American grasslands are ideal for the ecological establishment of anthrax and may have persisted for much of the Holocene epoch, possibly over 10,000 years."

Researchers had expected to find that strains of Anthrax in Western North America were diversified as they migrated northwards. However, they found that the most ancient strains of anthrax were discovered in northern Canada, while the more recent ones were found further south.

It appears that humans may have carried the bacteria to North America from Asia during the late Pleistocene epoch, when the two continents were linked together by the Beringian Steppe, researchers said. Once it was brought to North America, anthrax made its way south as an ice-free corridor opened in central Canada.

"The pattern just jumped out for anthrax coinciding with the peopling of the New World," geologist James Mead of East Tennessee State University in Johnson City, an author of the study, told USA Today.

"The idea is speculative at this point," Mead added.

In a previous study, the researchers found that the Ames strain of anthrax "“ known for being used in the 2001 attacks "“ have more recent origins that were traced to soil samples in Jim Hogg County in Texas during 2008.

The Ames strain has more common characteristics with the strains found in modern China, Mead said.

"It has been pretty clear for some time that Ames, as we know it, had originated in China and arrived somewhere in (New England) as a result of imported contaminated hair or hides, probably hair," Martin Hugh-Jones of Louisiana State University in Baton Rouge, who was not an author of the study, told USA Today.

"From the New England mills it made its way in the washing waters into local cattle downstream, and from their carcasses, into bone meals which were fed, eventually, to cattle in western and southern Texas."


Image Caption: Color-enhanced scanning electron micrograph shows splenic tissue from a monkey with inhalational anthrax; featured are rod-shaped bacilli (yellow) and an erythrocyte (red). Courtesy NIH


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