Seeing the world differently



Download 272.89 Kb.
Page6/9
Date conversion29.11.2016
Size272.89 Kb.
1   2   3   4   5   6   7   8   9

Single source


Waldor and colleagues have now sequenced the full DNA of the Haitian cholera and compared it with cholera from Peru, Bangladesh, the Gulf of Mexico and elsewhere. The analysis, done in record time using a new sequencing technique, confirmed a simpler analysis by the CDC last month, showing the Haitian bacteria were from a single source and similar to recent south Asian strains.

The greater genetic detail showed that the Haitian bacteria are "nearly identical" to the predominant south Asian strain, but a different lineage to cholera in South America, or strains occurring naturally in the Gulf of Mexico. "The bottom line is, this cholera was introduced by human activity from thousands of miles away," says Waldor.

Two mutations in both south Asian and Haitian bacteria mean they make the "classical" toxin seen in pandemics before the 1960s. The classical toxin is thought to cause worse disease than the toxin from the cholera strain that has been spreading around the world since 1961.

The Haitian toxin also carries a third mutation that appeared in 2002 in Bangladesh, and was until very recently found only in south Asia. The 2002 mutation has allowed the bacteria to almost totally replace the previous strain in south Asia, says Stephen Calderwood of the Massachusetts General Hospital in Boston, co-author of the sequencing report.

In the same way, the Haitian cholera could displace strains that have circulated in South America since 1991 if it gets loose there, Calderwood says. The bacteria exchange genes promiscuously, so new hybrids, with unpredictable properties, could also arise.

Tough and intense


This is bad news, as the Haitian strain carries more antibiotic-resistance genes than South American cholera. Its mutant toxin also seems to cause more intense diarrhoea – which is how cholera kills. The CDC says people have died a mere 2 hours after first getting symptoms.

Meanwhile, with predictions of eventual case numbers climbing from 400,000 to 650,000 in just one week, there seems no end in sight for Haiti's epidemic. Aid workers have already carried cholera abroad, though no secondary epidemics have yet been spawned.

Waldor and his colleagues are calling for vaccination and better sanitation in Haiti, to "minimise the spread of the new south Asian strain, and the virulence genes it carries, beyond the shores of this Caribbean island".

Journal reference: New England Journal of Medicine, in press



http://news.nationalgeographic.com/news/2010/12/101210-stonehenge-balls-ball-bearings-science-rolled/

Stonehenge Built With Balls?

New experiment suggests monumental stones could have rolled on rails.

It's one of Stonehenge's greatest mysteries: How did Stone Age Britons move 45-ton slabs across dozens of miles to create the 4,500-year-old stone circle?

Now a new theory says that, while the ancient builders didn't have wheels, they may well have had balls.

A previous theory suggested that the builders used wooden rollers - carved tree trunks laid side by side on a constructed hard surface. Another imagined huge wooden sleds atop greased wooden rails.

But critics say the rollers' hard pathway would have left telltale gouges in the landscape, which have never been found. And the sled system, while plausible, would have required huge amounts of manpower - hundreds of men at a time to move one of the largest Stonehenge stones, according to a 1997 study.



U.K. archaeology students attempt to prove a rail-and-ball system could have moved Stonehenge stones. Kate Ravilious in York, U.K. for National Geographic News

Andrew Young, though, says Stonehenge's slabs, may have been rolled over a series of balls lined up in grooved rails, according to a November 30 statement from Exeter University in the U.K., where Young is a doctoral student in biosciences.

Young first came up with the ball bearings idea when he noticed that carved stone balls were often found near Neolithic stone circles in Aberdeenshire, Scotland (map).

"I measured and weighed a number of these stone balls and realized that they are all precisely the same size - around 70 millimeters [3 inches] in diameter - which made me think they must have been made to be used in unison, rather than alone," he told National Geographic News.

The balls, Young admitted, have been found near stone circles only in Aberdeenshire and the Orkney Islands (map) - not on Stonehenge's Salisbury Plain.

But, he speculated, at southern sites, including Stonehenge (map), builders may have preferred wooden balls, which would have rotted away long ago. For one thing, wooden balls are much faster to carve. For another, they're much lighter to transport.


Proof of Concept


To test his theory, Young first made a small-scale model of the ball-and-rail setup.

"I discovered I could push over a hundred kilograms [220 pounds] of concrete using just one finger," he said.

With the help of his supervisor, Bruce Bradley, and partial funding from the PBS series Nova, Young recently scaled up his experiment to see if the ball-and-track system could be used to move a Stonehenge-weight stone. Sure enough, they found that, with just seven people pushing, they could easily move a four-ton load - about as heavy as Stonehenge's smaller stones.

Using the ball system, Young said, "I estimate it would be possible to cover 20 miles [32 kilometers] in a day" by leapfrogging track segments.

But the inner circle's "sarsen" stones weigh not 4 tons but up to about 45 tons. Young suspects a Stone Age system could have handled much heavier loads than his experimental one.

For one thing, he thinks oxen, not people, provided the pulling power - an idea supported by the remains of burned ox bones found in ditches around many stone circles.

For another, Britain's old-growth forests hadn't yet been razed 4,500 years ago, so the builders would have had easy access to cured oak. This tough wood - which was beyond the modern project's budget - would have resulted in a stronger, more resilient system than the soft, "greenwood" system the researchers built.

1   2   3   4   5   6   7   8   9


The database is protected by copyright ©dentisty.org 2016
send message

    Main page