Lyme disease

Lyme disease
Caption	Borrelia burgdorferi, the primary causative bacterium.
Field	Infectious disease

Lyme disease. It is an infectious disease caused by bacteria of the Borrelia genus, primarily Borrelia burgdorferi in North America. The illness is transmitted to humans through the bite of infected black-legged ticks, commonly known as deer ticks. Early diagnosis and treatment are critical to prevent more serious, disseminated complications.

Signs and symptoms

The initial stage often features a characteristic expanding rash called erythema migrans, which can appear at the site of the tick bite within days to weeks. Patients may also experience fatigue, fever, headache, and myalgia. Without treatment, the infection can disseminate, leading to neurological manifestations such as facial nerve palsy or meningitis. Later stages may involve arthritis, particularly in large joints like the knee, and cardiac issues such as atrioventricular block. The variety of symptoms can sometimes lead to misdiagnosis as other conditions like chronic fatigue syndrome.

Cause and transmission

The disease is caused by spirochete bacteria in the Borrelia burgdorferi sensu lato complex. In the United States, the primary agent is Borrelia burgdorferi sensu stricto, while in Europe and Asia, Borrelia afzelii and Borrelia garinii are more common. Transmission occurs through the bite of infected Ixodes scapularis or Ixodes pacificus ticks in North America, and Ixodes ricinus in Europe. These ticks acquire the bacterium by feeding on infected reservoir hosts, primarily small mammals like the white-footed mouse. White-tailed deer are important hosts for the adult ticks but do not transmit the bacteria.

Diagnosis

Diagnosis is primarily clinical, based on symptoms, potential tick exposure, and the presence of erythema migrans. For disseminated cases, serological testing is used, typically following a two-tiered protocol established by the Centers for Disease Control and Prevention. This involves an initial enzyme-linked immunosorbent assay or immunofluorescence assay, followed by a confirmatory Western blot. Other tests, like polymerase chain reaction on synovial fluid, can be helpful in diagnosing Lyme arthritis. Differential diagnosis must consider conditions like Southern tick-associated rash illness and multiple sclerosis.

Prevention

Primary prevention focuses on avoiding tick bites in endemic areas. This includes using insect repellent containing DEET, wearing protective clothing, and performing thorough tick checks after outdoor activities. Prompt and proper tick removal with fine-tipped tweezers can reduce transmission risk. In high-risk areas, a single prophylactic dose of doxycycline may be recommended after a tick bite under specific guidelines. Landscape management, such as creating tick-safe zones, and controlling tick populations through acaricide applications are broader public health strategies.

Treatment

The standard treatment for early localized disease is a course of oral antibiotics, such as doxycycline, amoxicillin, or cefuroxime axetil. For more severe manifestations, including neurological or cardiac involvement, intravenous antibiotics like ceftriaxone or penicillin G are often required. Treatment duration typically ranges from 14 to 28 days depending on the stage and symptoms. The Infectious Diseases Society of America publishes widely followed guidelines for management. Some patients with persistent symptoms after treatment are described as having post-treatment Lyme disease syndrome.

Prognosis and complications

Most patients treated with appropriate antibiotics in the early stages recover completely. A minority may develop chronic symptoms, often termed post-treatment Lyme disease syndrome, characterized by persistent pain, fatigue, and cognitive difficulties. Possible severe complications include chronic Lyme arthritis, encephalopathy, and Lyme carditis, which can involve inflammation of the heart. Rarely, infection during pregnancy can lead to adverse outcomes. Research into persistent symptoms is ongoing at institutions like the National Institutes of Health.

Epidemiology

It is the most common vector-borne disease in the Northern Hemisphere. In the United States, high-incidence states include Connecticut, Massachusetts, Minnesota, New Jersey, and Pennsylvania. The disease was first identified following a cluster of arthritis cases in Lyme, Connecticut, in the 1970s. Incidence in Europe is significant, with high rates reported in countries like Slovenia and Austria. Climate change and land use patterns are studied for their impact on the geographic expansion of Ixodes tick populations and incidence rates.

Category:Zoonoses Category:Bacterial diseases Category:Tick-borne diseases