Lyme Disease’s Possible Bacterial Predecessor Found in Ancient Tick
Excerpted from the Scientific American: (06/05/2014)
Ancient evidence of a familiar foe has emerged in a fossil tick infested with what appears to be spirochetes, a group of rotini-shaped bacteria responsible formany human diseases. The spirochetes in question closely resemble those of modern-day Borrelia, the genus responsible for Lyme disease. The finding, recently described in Historical Biology, could offer insight into the evolutionary history of the Lyme disease–causing pathogen that plagues people today, but is also notable for its novelty.
“This is the first evidence of spirochetes in a fossil tick prior to Homo,” says George Poinar, Jr., a paleoentomologist and parasitologist at Oregon State University, and author of the new paper. Although Lyme disease did not exist back then, the spirochetes in the fossil tick probably contributed to the genetic diversity of the 12 or more species of Borrelia that cause Lyme and similar diseases today, he says.
Parasites represent at least half of all modern animal species, and that distribution probably held true millions of years ago, too. “In a sense, this [finding] is not surprising since virtually every species on the planet is parasitized,” says Armand Kuris, a parasitologist at the University of California, Santa Barbara, who was not involved in the study. Evidence of those ancient parasite–host associations is difficult to come by, however. “In terms of finding any kind of physical documentation in the fossil record, that’s really rare—especially for a microbial pathogen,” Kuris says. “That’s what makes this paper just plain interesting.”
The spirochete-carrying tick—a juvenile—turned up in a 15-million- to 20-million-year-old piece of amber, along with three other young ticks that did not reveal any spirochetes. Poinar acquired the specimen nearly 25 years ago during a visit to the Dominican Republic’s amber mines. It was not until he recently took a closer look with a powerful compound microscope—magnifying the specimen up to 1,000 times—that he noticed the tiny ticks within.