Lyme disease is a tick-transmitted infection caused by Borrelia burgdorferi, a bacterial organism. Lyme disease was first recognized in 1975 when a close clustering of human cases occurred in Lyme, Connecticut; it is now the most commonly reported tick-borne illness in the US, with cases documented in every state except Montana.
Ixodes scapularis, known as the deer tick or black-legged tick, is the primary vector for Lyme disease, but at least two other types of ticks are known to carry the Lyme organism: Ixodes pacificus (the western black-legged tick) and Amblyomma americanum (the Lone Star tick).
In the US, the main animal reservoir for B. burgdorferi is the white-footed mouse, which is the preferred host for young deer ticks. Tick nymphs and larvae become infected when they feed on the mice and then transmit the organism when they move to new hosts.
Deer are often the hosts for adult ticks, but deer do not appear to develop Lyme disease. Humans can contract the disease from either immature or adult ticks. There is no convincing evidence that fleas, mosquitoes, or flies transmit Lyme disease, and blood products (i.e., transfusions) have not been associated with transmission of the disease. (Bratton R, Corey G. Tick-borne disease. Am Fam Physician 2005;71:2323-30, 2331-2)
Over 90% of infections occur along the eastern US coast from Massachusetts to Maryland, and in California, Minnesota, Oregon, and Wisconsin. Lyme also occurs in Europe, Russia, China, and Japan. (The Merck Manual, 18th Edition. 2006:1478-81)
Most cases of Lyme disease occur in the spring and summer months, and most patients are children and young adults who live near wooded areas. However, individuals who rarely venture far afield have also contracted Lyme disease, probably while engaging in yard work or from ticks brought indoors by family pets (dogs can develop Lyme disease, too).
Animal studies show that infected tick nymphs must remain attached for 36 to 48 hours before transmitting Lyme disease, while adult ticks must remain attached for 48 to 72 hours. Therefore, early detection and removal of ticks is a key to prevention of Lyme disease.
Signs and Symptoms of Lyme Disease
Lyme disease exhibits three phases with distinct signs and symptoms:
- Early localized: Erythema migrans (EM), the hallmark rash of Lyme disease, occurs in 80% of infected individuals. Three to 30 days after a tick bite, EM begins as a red pimple or spot—usually on the trunk or on an extremity near the trunk—and then expands. The center often clears, forming a “bulls-eye”. Untreated patients may develop multiple similar lesions in other areas of the body. EM usually lasts a month or so. Treatment prevents progression to later stages.
- Early disseminated: Several days to weeks after EM, a flu-like syndrome develops: fatigue, chills, fever, headache, stiff neck, and joint and muscle pain may last for several weeks. Since these symptoms are nonspecific, people who didn’t develop EM—or those who ignored its appearance—are often misdiagnosed with other conditions, such as fibromyalgia.
- Late: Months to years following infection, neurologic, cardiac, and skeletal manifestations may occur. Bell’s palsy (paralysis of the face) is a classic neurologic sign. Neuropathies, meningitis-like syndromes, cardiac arrhythmias, pericarditis, heart failure, and arthritis are common late manifestations in untreated patients.
Late diagnosis of Lyme disease is difficult, due in part to variable seroconversion in infected individuals. ELISA, Western blot, tissue fluid cultures and PCR are all utilized, but none is 100% sensitive or specific. In addition, some localities require documentation of the EM rash by health professionals, which presents a distinct barrier to appropriate management.
Effective tick repellants, adequate clothing, early removal of ticks, and recognition of early signs of infection remain the primary methods for dealing with Lyme disease.
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