Lyme Disease: Causes and symptoms

Lyme disease is caused by Borrelia burgdorferi. Once Borrelia burgdorferi gains entry to the body through a tick bite, it can move through the bloodstream quickly. Only 12 hours after entering the bloodstream, Borrelia burgdorferi can be found in cerebrospinal fluid (which means it can affect the nervous system). Treating Lyme disease early and thoroughly is important because lyme disease can hide for long periods within the body in a clinically latent state. That ability explains why symptoms can recur in cycles and can flare up after months or years, even over decades. It is important to note, however,

that not many people who are exposed to Borrelia burgdorferi develops the disease.

Lyme disease is usually described in terms of length of infection (time since the person was bitten by a tick infected with lyme disease) and whether Borrelia burgdorferi is localized or disseminated (spread through the body by fluids and cells carrying Borrelia burgdorferi). Furthermore, when and how symptoms of Lyme disease appear can vary widely from patient to patient. People who experience recurrent bouts of symptoms over time are said to have chronic lyme disease.

The most recognizable indicator of Lyme disease is a rash around the site of the tick bite. Often, the tick exposure has not been recognized. The eruption might be warm or itch. The rash—erythema migrans (EM) generally develops within three to 30 days and usually begins as a round, red patch that expands outward. About 75% of patients with Lyme disease develop EM. Clearing may take place from the center out, leaving a bull's-eye effect; in some cases, the center gets redder instead of clearing. The rash may look like a bruise on people with dark skin. Of those who develop lyme disease, about 50% notice flu-like symptoms, including fatigue, headache, chills and fever, muscle and joint pain, and lymph node swelling. However, a rash at the site can also be an allergic reaction to the tick saliva rather than an indicator of lyme disease, particularly if the rash appears in less than three days and disappears only days later.

Weeks, months, or even years after an untreated tick bite, symptoms can appear in several forms, including:

• fatigue, forgetfulness, confusion, mood swings, irritability, numbness
• neurologic problems, such as pain (unexplained and not triggered by an injury), Bell's palsy (facial paralysis, usually one-sided but may be on both sides), and a mimicking of the inflammation of brain membranes known as meningitis (fever, severe headache)
• arthritis (short episodes of pain and swelling in joints) and other musculoskeletal complaints. Arthritis eventually develops in about 60% of patients with untreated lyme disease

Less common effects of Lyme disease are heart abnormalities (such as irregular rhythm or cardiac block) and eye abnormalities (such as swelling of the cornea, tissue, or eye muscles and nerves).

— Rebecca J. Frey, PhD