Lyme disease, older than humans

Fossil ticks containing bacteria resembling Lyme disease were found embedded in 15-million-year old amber

By Graciela Matrajt

As you plan for your next hike in the woods, remember to watch out for ticks, which are vectors of several illnesses, among which there is the bacterial infection known as Lyme disease.

A recent study found 15-million-year-old fossil ticks that contain structures that resemble bacteria. The structures have the same size and shape as the spirochete-type bacteria Borrelia, the microorganism that causes Lyme disease. This discovery suggests that Lyme disease would have been in existence before human beings evolved, about 125,000 years ago.

George Poinar, professor emeritus in the Department of Integrative Biology at Oregon State University performed the research, which was published this year in the journal Historical Biology. Poinar is one of the leading experts on plant and animal fossils preserved in a viscous tree resin, called amber, which can trap and preserve material as it slowly flows and solidifies. Poinar has been studying diseases revealed in fossil records for 30 years. He has found evidence of illness-causing microorganisms, called pathogens, related to the diseases Malaria, Leishmania, and now Lyme disease. “Learning about the origin of human pathogens is crucial for understanding how they evolve today,” says Poinar.

 Poinar surveyed amber samples recovered from mines in the Dominican Republic. He found ticks that contain bacteria-like structures in their digestive tubes and were between 15 and 20 million years old. Then, he analyzed tick larvae using an optical microscope that allows magnification up to 1000 times.

Inside one larva, Poinar found a large population of spirochete-like structures, which appear as black elongated features with similar shape and size as the bacterium Borrelia. “Although this morphology resembles spirochetes, these could also be fibers that were trapped in the amber along with the tick. It is hard to state, based on shape and size alone, that this is Borrelia,” says amber fossil expert Raul Cano, professor emeritus of Microbiology at the Biological Sciences Department, California Polytechnic State University.

Yet, if these structures were fibers, they should be present in all four larvae, but Poinar only found them in one specimen. Moreover, Borrelia are the only spirochetes that occur in ticks. “Collectively, these lines of evidence make a strong case for these structures being Borrelia,” says insect and pathogen fossil expert Conrad Labandeira, curator in the Department of Paleoentomology at the Smithsonian National Museum of Natural History.

However, “caution is needed when interpreting these structures as spirochetes,” recommends spirochete expert Alan Barbour, professor of Medicine and Microbiology at the University of California. “Spirochetes are characterized by their motion filaments, called flagella, which run along and inside the cell and which can only be detected by very high magnification microscopy, known as electron microscopy,” explains Barbour.

But to analyze these structures with electron microscopy researchers need to crack open the amber to expose the ticks. “Most ticks I investigated are free of spirochete-like structures,” says Poinar. Additionally, “spirochete cells are very fragile and get easily damaged during specimen preparation,” says Cano.

This is not the first time Poinar found fossils of human pathogens. In previous studies, he reported Rickettsia-like cells, the bacteria that cause Rocky Mountain spotted fever and Typhus, found inside 100 million-year-old fossilized ticks.