What Causes Lyme Disease?

Borrelia Burgdorferi

Lyme disease is an infection caused by several strains of the bacteria Borrelia burgdorferi(Bb). The bacteria is transmitted to humans through the bite of an infected tick. These ticks can also transmit other diseases and infect pets and livestock.

The tick that transmits Lyme is so small you may not notice it. The tick’s saliva contains an anesthetic-like substance that numbs your skin so you may not feel the bite. The ticks that spread Lyme are typically no larger than a sesame seed (or the size of a period at the end of a sentence). It is thought that nymphs infect more humans than adult ticks because they are so hard to see.

The Blacklegged Tick

In the United States, the Western blacklegged tick, or Ixodes pacificus, is responsible for spreading Lyme disease on the West Coast. On the East Coast and in several mid-western states, it is the Eastern blacklegged tick, also known as the “deer tick,” or Ixodes scapularis, that spreads Lyme.

All in all, according to Lyle Peterson from the Centers for Disease Control and Prevention (CDC), there are 80 million Americans living in areas of highest risk for Lyme disease where these ticks are common.

Host Animals

A tick emerges from an egg and feeds on different animals (or “hosts”) during its larval, nymph, and adult stages. A tick can live for several years on just a handful of blood meals.

The tick most often becomes infected during its larval or nymph stage, when it feeds off small animals like squirrels, mice, or birds that carry the bacteria which causes Lyme disease (Borrelia burgdorferi or Bb). These animals can also carry other bacteria. Click here to watch a video detailing the ways ticks stick to the skin (with accompanying article from The New York Times, published October 29, 2013).

The tick, now infected, then passes on the bacteria to a human or another animal during its next feeding cycle. The small animal most responsible for transmitting the Bb bacteria to ticks varies by region.