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.)

This is an engorged deer tick (Ixodes dammini) embedded in the skin of a human host. In the United States, these ticks are the primary source of Lyme disease. (Image courtesy of the Centers for Disease Control and Prevention and M. Fergione.)

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.)

This is an adult female deer tick, Ixodes dammini. It transmits Lyme disease and babesiosis to humans. (Image courtesy of the Centers for Disease Control and Prevention.)

Ticks are small, insect-like creatures that live in woods and fields. They can attach to people or animals as they brush past bushes, plants, and grass. Ticks can be fairly large, as big as a pencil eraser, or so small that they are almost impossible to see. While most ticks do not carry diseases, some ticks can cause Lyme disease, Rocky Mountain spotted fever, Colorado tick fever, and tularemia.

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.