Lyme Disease Basics

Lyme disease is a tick-borne infectious disease caused by the spirochete bacterium Borrelia burgdorferi (in North America) and transmitted to humans through the bite of infected Ixodes (black-legged or deer) ticks. It is the most common vector-borne disease in North America and Europe. The Ixodes tick has a two-year life cycle with three feeding stages (larva, nymph, adult), and each stage requires a blood meal. The primary reservoir hosts are white-footed mice (for larvae and nymphs) and white-tailed deer (for adult ticks). Nymphal ticks are responsible for most human infections because they are very small (approximately 1-2 mm, the size of a poppy seed) and often go undetected. After the tick attaches and begins feeding, it takes approximately 36-48 hours of attachment for the spirochete to be transmitted from the tick's midgut to its salivary glands and into the host. This critical window means that early tick removal significantly reduces transmission risk. Once inoculated into the skin, Borrelia burgdorferi multiplies locally and produces outer surface proteins that facilitate tissue invasion. The organism disseminates through the bloodstream and lymphatics to distant...