How does Lyme disease start?

Lyme disease is an infectious disease caused by a spiral-shaped bacterium of the *Borrelia* genus, which is transmitted to humans through the bite of infected ticks. In the early stages of the disease, symptoms include fever, headache, fatigue, and a characteristic skin lesion called erythema migrans. Erythema migrans typically appears as a circular rash with a red border and a paler center, resembling a "bull's-eye." If left untreated, the bacteria can spread to various organs within days or weeks, leading to complications such as meningitis (inflammation of the brain and spinal cord), encephalitis (inflammation of the brain), peripheral neuritis (inflammation of the peripheral nerves), myocarditis (inflammation of the heart muscle), arrhythmias (irregular heartbeats), and musculoskeletal pain. Early and appropriate treatment with antibiotics is crucial; otherwise, the disease can become chronic and difficult to treat.

Affected areas:

Skin, brain, peripheral nerves, heart, musculoskeletal system

The clinical course progresses through three stages:

1. Early Localized Infection: After an incubation period of 3 to 32 days following a tick bite, erythema migrans (a characteristic rash with a red border and paler center, resembling a bull's-eye) appears on the skin. The skin may be red or raised, with the affected area enlarging, the edges becoming redder, and the center fading.
2. Early Disseminated Infection: Days to weeks later, the *Borrelia* bacteria spread through the bloodstream, causing multiple skin lesions and symptoms such as severe headache, stiff neck (meningismus), fever, chills, and fatigue. Muscle and joint pain are common, with pain migrating through joints, tendons, muscles, and bones; usually affecting one or two joints at a time without swelling. Swollen lymph nodes and spleen may occur, along with sore throat, dry cough, conjunctivitis (inflammation of the conjunctiva of the eye), or testicular swelling. Fatigue persists, but initial symptoms often recur intermittently. The nervous system may be affected, causing meningitis or encephalitis, and in some cases, the heart may be affected, leading to arrhythmias.
3. Late Persistent Infection: This stage is characterized by musculoskeletal symptoms, often developing months after infection. It can involve arthritis, particularly affecting large joints like the knee. Cognitive impairment (memory problems), mood disorders, and sleep disturbances may also occur, along with pain in the spinal roots.
    

Cause:

Several pathogens belonging to the *Borrelia* genus, a difficult-to-culture gram-negative spirochete, cause Lyme disease. *Borrelia burgdorferi* is the most common causative agent. Lyme disease is prevalent in North America.
 

Affected Body Systems:

Skin, brain, peripheral nerves, heart, musculoskeletal system
 

Diagnosis:

Diagnosis is based on medical history and physical examination. Serological testing may be helpful if characteristic erythema migrans is absent.
 

Tests:

While culturing the bacteria from skin lesions, serum, or cerebrospinal fluid provides definitive diagnosis, it's difficult to perform. Therefore, serological testing (ELISA followed by Western Blot if positive or indeterminate) is most commonly used. In later stages, polymerase chain reaction (PCR) to detect bacterial DNA in joint fluid may be used.
 

Treatment:

Early localized Lyme disease (with erythema migrans) is treated with oral antibiotics such as doxycycline (200 mg/day, divided twice daily), amoxicillin (1.5 g/day, divided thrice daily), or cefuroxime (1 g/day, divided twice daily) for 10-21 days. Doxycycline is contraindicated in children under 8 years of age, pregnant women, and breastfeeding mothers. Symptoms may persist in about 45% of patients after treatment, but additional antibiotics are usually not necessary. Macrolide antibiotics are less effective than amoxicillin or doxycycline and are not the first-line choice; first-generation cephalosporins are ineffective against Lyme disease.
For early disseminated Lyme disease, including facial nerve palsy or mild first-degree atrioventricular block, 2-3 weeks of oral antibiotics may suffice. However, more severe cardiac involvement (second or third-degree atrioventricular block, myocarditis) or meningitis requires intravenous antibiotics such as ceftriaxone (2 g/day), cefotaxime (6 g/day), or penicillin G (1.8-2.4 million units/day) for 2-3 weeks. For arthritis without neurological symptoms following antibiotic treatment, a 4-week course of antibiotics is recommended. For arthritis with neurological symptoms or persistent, recurrent symptoms despite treatment, 2-4 weeks of antibiotics may be necessary. Amoxicillin (50 mg/kg/day, divided thrice daily) is used for children under 8 years old. Cefuroxime or, less effectively, macrolides can be used as second-line agents in patients who cannot take tetracycline or penicillin. Patients with positive serological tests but no symptoms are generally observed without antibiotic treatment.
Treatment may fail regardless of the antibiotic used, necessitating retreatment.
 

Course and Complications:

Early treatment usually leads to complete recovery. However, delayed diagnosis, inadequate antibiotic therapy, co-existing illnesses, or immunocompromised status can lead to complications. In these cases, fatigue, musculoskeletal pain, and neurological symptoms may persist for years, and rarely, death may occur.