It all started in the small town of Lyme, Connecticut. For years, doctors had been diagnosing children with a type of juvenile rheumatoid arthritis that had begun popping up in the area. But it wasn’t until 1975 that the condition was conclusively identified as something separate, and named after the town where it was first observed.
In the decades since this discovery, the tickborne pathogen has spread to a number of new states and into Canada. In the U.S., Lyme disease is (by far) the most common tickborne illness, with the CDC recording around 30,000 cases annually. What's more, not all cases are reported, and the agency estimates that as many as half a million Americans are diagnosed with the disease each year.
Let's dig into the science behind how — and why — Lyme disease has managed to spread so far.
What Is Lyme Disease and How Do You Get It?
In humans, Lyme disease is caused by several related corkscrew-shaped bacteria called spirochetes. Most cases in North America are caused by the bacterium Borrelia burgdorferi, while B. mayonii, on rare occasions, is responsible for infections in the Midwest. The natural reservoir for these bacteria are small mammals like the white-footed mouse.
