The cause of Lyme disease is the spirochete Borrelia burgdorferi that is transmitted to humans by the small tick Ixodes dammini or other ticks in the Ixodidae family. The tick injects spirochete-laden saliva into the bloodstream or deposits fecal matter on the skin. This multisystemic disease usually begins in the summer with a skin lesion called erythema chronicum migrans (ECM), followed by more lesions, a malar rash, conjunctivitis, and urticaria. The lesions are eventually replaced by small red blotches. Other common symptoms in the first stage include fatigue, intermittent headache, fever, chills, and muscle aches.

In stage two, which can be weeks or months later, cardiac or neurologic abnormalities sometimes develop. In the last stage (weeks or years later) arthritis develops with marked swelling, especially in the large joints. If tetracycline, penicillin, or erythromycin is given in the early stages, the later complications can be minimized. High dosage of intravenously given penicillin can also be effective on the late stages.