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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 95% -- are reported in these 13 states:

  • Connecticut
  • Delaware
  • Maine
  • Maryland
  • Massachusetts
  • Minnesota
  •  New Hampshire
  • New Jersey
  • New York
  • Pennsylvania
  • Vermont
  • Virginia
  • Wisconsin

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 should be knowledgeable about Lyme disease.

Recommended Related to Arthritis

Avascular Necrosis (Osteonecrosis)

Avascular necrosis (AVN), also called osteonecrosis, aseptic necrosis, or ischemic bone necrosis, is a condition that occurs when there is loss of blood to the bone. Because bone is living tissue that requires blood, an interruption to the blood supply causes bone to die. If not stopped, this process eventually causes the bone to collapse. Avascular necrosis most commonly occurs in the upper leg. Other common sites are the upper arm, knees, shoulder, and ankles.

Read the Avascular Necrosis (Osteonecrosis) article > >

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 can lead to Lyme arthritis.

WebMD Medical Reference

Reviewed by Melinda Ratini, DO, MS on March 23, 2014

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