Lyme disease is a stealthy（鬼鬼祟祟的）, often misdiagnosed disease that was only recognized about 40 years ago, but new discoveries of ticks fossilized in amber show that the bacteria which cause it may have been lurking around for 15 million years -- long before any humans walked on Earth. The findings were made by researchers from Oregon State University, who studied 15-20 million-year-old amber from the Dominican Republic that offer the oldest fossil evidence ever found of Borrelia, a type of spirochete（螺旋体）-like bacteria that to this day causes Lyme disease. They were published in the journal Historical Biology.

In a related study, published in Cretaceous Research, OSU scientists announced the first fossil record of Rickettsial-like cells, a bacteria that can cause various types of spotted fever. Those fossils from Myanmar were found in ticks about 100 million years old.

As summer arrives and millions of people head for the outdoors, it's worth considering that these tick-borne diseases may be far more common than has been historically appreciated, and they've been around for a long, long time.

"Ticks and the bacteria they carry are very opportunistic," said George Poinar, Jr., a professor emeritus in the Department of Integrative Biology of the OSU College of Science, and one of the world's leading experts on plant and animal life forms found preserved in amber. "They are very efficient at maintaining populations of microbes in their tissues, and can infect mammals, birds, reptiles and other animals.

"In the United States, Europe and Asia, ticks are a more important insect vector of disease than mosquitos," Poinar said. "They can carry bacteria that cause a wide range of diseases, affect many different animal species, and often are not even understood or recognized by doctors.

"It's likely that many ailments（疾病） in human history for which doctors had no explanation have been caused by tick-borne disease."

Lyme disease is a perfect example. It can cause problems with joints, the heart and central nervous system, but researchers didn't even know it existed until 1975. If recognized early and treated with antibiotics, it can be cured. But it's often mistaken for other health conditions. And surging deer populations in many areas are causing a rapid increase in Lyme disease -- the confirmed and probable cases of Lyme disease in Nova Scotia nearly tripled in 2013 over the previous year.