Tuberculosis Helped Mastodon Extinction

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Tuberculosis Helped Bring Down Mastodons Ker Than

LiveScience Staff Writer

LiveScience.com Sun Sep 24, 11:00 AM ET

A tuberculosis pandemic among an ancient mammoth-like creature

probably contributed to the great beasts' demise, a new study

suggests.

Scientists examining mastodon skeletons found a type of bone damage

in several of the animal's foot bones that is unique to sufferers of

tuberculosis. The disease would have weakened and crippled the

animals, making them more vulnerable to humans and climate change,

two factors that scientists have long speculated were behind their

extinction in North America.

Mastodons were ancient elephants that resembled mammoths, but were

shorter and less hairy. Both species lived in North America and

disappeared mysteriously, along with other large mammals, around the

time of the last major Ice Age about 10,000 years ago.

A crippling disease

Researchers Bruce Rothschild of the Northeastern Ohio Universities

College of Medicine and Laub of the Buffalo Museum of Science

in New York looked at 113 mastodon skeletons and found signs of

tuberculosis in 59 of them. That's 52 percent.

Tuberculosis is a bacterial infection that commonly infects the

lungs. It can also affect other parts of the body, including organs

and bones. In humans, only about 1 to 7 percent of infected

individuals develop bone damage. The fact that more than half of the

mastodon skeletons examined had the bone lesions suggests

tuberculosis was a " hyperdisease " that afflicted a large percentage

of the North American mastodon population.

When tuberculosis infects bone, it creates a tell-tale type of damage

in which bone beneath cartilage is carved out, or " excavated. "

The infected mastodons were different ages and sizes and came from

all over North America. They lived at different times, too. The

disease appears to have struck the creatures as early as 34,000-years-

ago and persisted in the species until as recently as 10,000- years-

ago.

That the disease was widespread and yet persisted for so long in the

species suggests it was not immediately lethal, Rothschild said.

Instead, it was probably a chronic disease, one that gradually

weakened rather than killed the animals.

Mastadon stressors

In humans, tuberculosis can lay dormant for several years after

initial infection, repressed by the body's own immune system. But it

can flare up into full-blown disease during times of stress. A

similar flare-up probably happened with the mastodons during times of

stress, Rothschild said.

Mastadons living at the end of the last Ice Age had reasons to be

stressed. They faced not only a drastically changing world brought

about by rapid climate change, but also the arrival of a new threat:

weapon-wielding humans that hunted them for food.

Together, these three factors—disease, climate change and humans—

might have been too much for the creatures. Weakened by tuberculosis,

the beasts would have been less able to ward off other diseases, and

the crippling bone damage would have affected their ability to walk.

" Extinction is usually not a one-phenomenon event, " Rothschild told

LiveScience.

A route of infection

But how did North American mastodons first get tuberculosis, a

disease whose first known documentation is in a 500,000-year-old

buffalo in China?

Rothschild thinks he knows the answer. In a separate study, he and

Larry from the Natural History Museum in Kansas found similar

tuberculosis-caused bone damage in North American bovids, a group of

animals that included bison, musk oxen and bighorn sheep.

Tuberculosis appears to have been just as prevalent in the bovids as

in the mastodons, but the record of infection for this group of

animals stretches back much further—at least 75,000 years.

Bison and other bovids are believed to have originated in Asia and

crossed into North America using the Bering Land Bridge, which

connected the two continents. Humans made the same journey much later.

The researchers speculate that some of the bovids were probably

already infected with tuberculosis when they migrated into the New

World. Once in North America, the bovids could have spread to

mastodons and other species, possibly even humans, Rothschild said.

Both the mastodon and bovid studies will be detailed in upcoming

issues of the science journal Naturwissenchaften.

http://asia.fullcoverage./s/space/20060924/sc_space/tuberculo

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