Lyme disease is a bacterial infection caused by the spirochete bacterium Borrelia burgdorferi.
Lyme disease is an infectious illness caused by a spiral-shaped bacterium known as Borrelia burgdorferi. This organism is carried and spread by certain species of ticks, most notably the black-legged tick—often referred to as the deer tick. When these ticks bite humans and remain attached long enough to feed, they can transmit the bacteria into the bloodstream, potentially leading to a wide array of symptoms.
What Is Lyme Disease?
Lyme disease is a tick-borne bacterial infection that can affect multiple body systems if not identified and treated early. Because the condition can mimic other illnesses and varies greatly from one person to another, it is sometimes difficult to diagnose. In the United States, the deer tick (Ixodes scapularis) is the most common carrier, while related tick species transmit the illness in other parts of the world. The disease often begins with localized symptoms but may progress to involve the skin, joints, nervous system, and even the heart if treatment is delayed.
How Lyme Disease Develops
The infection spreads almost exclusively through the bite of a tick that is already carrying Borrelia burgdorferi. Human-to-human transmission does not occur. Several key factors play a role in how Lyme disease is acquired:
Tick Bites from Infected Black-Legged Ticks
Black-legged ticks acquire the bacteria when they feed on infected animals such as mice or other small mammals. They may later pass the bacteria to humans during a blood meal.
Nymph Stage Transmission
Ticks progress through several life stages—larva, nymph, and adult. The nymph stage is responsible for most Lyme disease cases because nymphs are extremely small (about the size of a poppy seed) and often go unnoticed. Their tiny size allows them to remain attached long enough for transmission to occur.
Bacterial Entry Through the Skin
When an infected tick attaches and begins to feed, the Borrelia bacteria slowly move from the tick’s gut into the host’s skin and bloodstream. This process generally requires the tick to remain attached for many hours.
Symptoms and Disease Progression
Although symptoms vary, early Lyme disease often presents with:
- Expanding skin rash (commonly called erythema migrans)
- Fatigue, fever, and body aches
- Headache and swollen lymph nodes
If untreated, the infection may advance to cause joint swelling, nerve problems, or cardiac complications.
After Tick Bite Prophylaxis
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