The U.S. Centers for Disease Control and Prevention estimates that there about 300,000 cases of Lyme disease in the U.S. each year.

The stealthy, often misdiagnosed disease was discovered nearly 40 years ago in a town called Lyme, Connecticut, which is how it got its name.

However, newly discovered fossilized ticks show that the bacteria which cause the disease may have been around for 15 million years — long before 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 offers the oldest fossil evidence ever found of Borrelia, a type of spirochete-like bacteria that to this day causes Lyme disease. Their research was published in the journal Historical Biology.

This group of spirochetes, the type that causes Lyme disease, was identified in a tick preserved in amber. Photo by George Poinar, Jr., courtesy of Oregon State University.

“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. “They are very efficient at maintaining populations of microbes in their tissues, and can infect mammals, birds, reptiles, and other animals.

A series of four ticks from Dominican amber were analyzed in the study, revealing a large population of spirochete-like cells that most closely resemble those of the present-day Borrelia species. Bacteria are an ancient group that date back about 3.6 billion years, almost as old as the planet itself. As soft-bodied organisms, they are rarely preserved in the fossil record. However, amber is a free-flowing tree sap that can trap and preserve material in exquisite detail as it slowly turns into a semi-precious mineral.

In 30 years of studying diseases revealed in the fossil record, Poinar has documented the ancient presence of such diseases as malaria, leishmania, and others. Evidence even suggests that dinosaurs could have been infected with Rickettsial pathogens.

“It’s likely that many ailments in human history for which doctors had no explanation have been caused by tick-borne disease,” Poinar said.

Humans have probably been getting diseases, including Lyme disease, from tick-borne bacteria as long as there have been humans, according to Poinar. The oldest documented case is the Tyrolean iceman, a 5,300-year-old mummy found in a glacier in the Italian Alps.

“Before he was frozen in the glacier, the iceman was probably already in misery from Lyme disease,” Poinar said. “He had a lot of health problems and was really a mess.”

Lyme disease can cause problems with joints, the heart, and the 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 is often mistaken for other health conditions.

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.

“In the United States, Europe, and Asia, ticks are a more important insect vector of disease than mosquitoes,” 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.”

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– Spirochete-like cells in a Dominican amber Ambylomma tick (Arachnida: Ixodidae)