Understanding Lyme Disease -- the Basics

What Is Lyme Disease?

First identified in a group of children in Lyme, Connecticut, Lyme disease has now been found in nearly all states and 18 other countries. Most cases -- more than 90% -- are reported in three regions of the U.S.:

• Northeast, from Massachusetts to Maryland
• North Central States, mostly in Minnesota and Wisconsin
• West Coast, particularly Northern California

Because the symptoms are random and vague (aside from a bull's-eye rash), Lyme disease can be hard to diagnose. Unfortunately, unless Lyme disease is treated promptly, it can also be difficult to cure. For these reasons, people living in high-risk areas can have considerable anxiety about Lyme disease, and doctors tend to over-diagnose and over-treat it.

What Causes Lyme Disease?

Lyme disease is caused by bacteria transmitted through the bite of the tiny black-legged, or deer, tick found in the Eastern and Central U.S. and the western black-legged tick in the Pacific West. The riskiest months for Lyme disease are from May through September, when young ticks are likely to be biting.

In humans, the bacteria may cause flu-like symptoms. It invades many tissues -- including the heart and nervous system -- and triggers an immune response that leads to Lyme arthritis.