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GRANTS PASS, Ore. (AP) - Fossilized bacteria found inside a tick encased in 15 million-year-old amber indicates the bacteria that cause Lyme disease were likely around long before there were humans.

George Poinar Jr. bought the amber about 30 years ago in the Dominican Republic while researching the ancient origins of diseases spread by ticks and mosquitoes. Poinar is a professor emeritus of entomology at Oregon State University

He did not see the tick inside until five years ago. When he cracked open the amber, he could see with a powerful microscope that the tick was full of millions of fossilized bacteria.

Poinar writes in the online edition of the journal Historical Biology published April 22 that he could not extract a DNA sample for a positive identification of the fossilized bacteria, but its size and form were similar to the genus Borrelia, which includes the species that causes Lyme disease.

"This discovery represents the first record of spirochete-like cells associated with fossil ticks," he wrote.

The fossil record indicates that Homo sapiens have been around about 200,000 years. About 15 million years earlier, Poinar's tick would have tumbled into a glob of pitch that fossilized into a chunk of amber.

Poinar said there was no blood in the larval tick, indicating it probably became infested with the bacteria from its mother, rather than from feeding on an infected rodent.

Neither the tick, from the genus Amblyomma, nor the bacteria have changed much in the ensuing 15 million years, Poinar said.

Lyme disease infects tens of thousands of people each year. Ticks pick up the bacteria feeding on the blood of infected rodents, and pass them on to people when the ticks bite.

(Copyright 2014 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.)

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