Erythema chronicum migrans is the initial lesion of Lyme disease, and often appears at the site of the infecting tick bite. It is a red, enlarging rash, flat or slightly raised, and may reach from 4 to 20 inches across (the average rash is 6 inches). (Image courtesy of the Centers for Disease Control and Prevention.)

Borrelia burgdorferi is a spirochete bacteria that causes Lyme disease. It is similar in shape to the spirochetes that cause other diseases, such as relapsing fever and syphilis. (Image courtesy of the Centers for Disease Control and Prevention.)

Diseases are often carried by ticks, including Rocky Mountain Spotted Fever, Colorado Tick Fever, Lyme disease, and tularemia. Less common or less frequent diseases include typhus, Q-fever, relapsing fever, viral encephalitis, hemorrhagic fever, and babesiosis.

There are many species of ticks. Of these, a large proportion are capable of carrying disease. Diseases carried by ticks include Lyme disease, Erlichiosis, Rocky Mountain Spotted Fever, Colorado Tick Fever, tularemia, typhus, hemorrhagic fever, and viral encephalitis. (Image courtesy of the Centers for Disease Control and Prevention.)

Lyme disease is caused by a bacterium called Borreliaburgdorferi. It is known as a spirochete because of its long, corkscrew shape. This photograph shows the typical corkscrew appearance of a spirochete. (Image courtesy of the Centers for Disease Control and Prevention.)

Lyme disease is an acute inflammatory disease characterized by skin changes, joint inflammation and flu-like symptoms caused by the bacterium Borrelia burgdorferi transmitted by the bite of a deer tick. Symptoms resolve in 3 to 4 weeks even without treatment, but secondary or tertiary disease may develop if initial infection is not treated.

This is a close-up photograph of a tick embedded in the skin. Ticks are important because they can carry diseases such as Rocky Mountain spotted fever, tularemia, Colorado tick fever, Lyme disease, and others.