Some twenty million years ago, a flea became trapped in amber, and with it, a tiny bacteria that researchers think may be the ancestor of the bubonic plague, according to an article on eurekalert.com.

If it turns out to be related to Yersinia pestis, the plague bacteria, it would show the historic killing plague would be many times older than originally thought and would predate the human race.

The plague wiped out more than half of the population of Europe in the 14th century, when three phases of the disease, bubonic, septicemic and pneumonic, spread across the continent and Asia, killing an estimated 75 to 200 million people.

Today, in addition to humans, bubonic plague can infect many types of animals and is endemic to many countries, including the United States, where it has been detected in prairie dogs and other small animals.  Four people have died from the disease in 2015 in the U.S. despite the disease being treatable with antibiotics.

The scientists say they are not certain the bacteria are related to the Yersinia pestis, but the shape, size and characteristics are similar to modern strains of the bacteria.

George Poinar, Jr., an entomology researcher in the College of Science at Oregon State University, said, “Aside from physical characteristics of the fossil bacteria that are similar to plague bacteria, their location in the rectum of the flea is known to occur in modern plague bacteria.  And in this fossil, the presence of similar bacteria in a dried droplet on the proboscis of the flea is consistent with the method of transmission of plague bacteria by modern fleas.”

The fossil came from amber mines in an area that is now the Dominican Republic, and scientists say that area was a tropical rain forest millions of years ago.

Poinar added the human strains of the bacteria may have evolved some 10-to-20,000 years ago, noting these ancient strains could have appeared long before humans lived and would most certainly be extinct by now.