Lyme disease (aka Lyme borreliosis) is caused by bacteria from the Borrelia genus, and is the most common tick-borne disease in the Northern Hemisphere. Borrelia burgdorferi sensu stricto is the main cause of Lyme disease in North America, whereas Borrelia afzelii and Borrelia garinii cause most European cases. Borrelia is transmitted to humans through the bite of infected ticks belonging to a few species of the genus Ixodes ("hard ticks" ). The disease is named after the towns of Lyme and Old Lyme, Connecticut, where a number of cases were identified in 1975. Although it was realized that Lyme disease was a tick-borne disease in 1978, the cause of the disease remained a mystery until 1981, when B. burgdorferi was identified.
Deer Tick
Nymphal and adult deer ticks can be carriers of Lyme disease. Nymphs are about the size of a poppy seed.
Lyme disease can affect multiple body systems and produce a range of symptoms, though not all patients with Lyme disease will have all symptoms, and many of the symptoms are not specific to Lyme disease. The incubation period from infection to the onset of symptoms is usually one to two weeks, but can be much shorter (days), or much longer (months to years). Most infections are caused by ticks in the nymphal stage, as they are very small and may feed undetected for long periods of time, with symptoms occurring most often from May through September because of this life cycle. An infected tick must be attached for at least a day for transmission to occur, and only about 1% of recognized tick bites result in Lyme disease.
Lyme disease begins with a localized infection, affecting the area at the site of the tick bite with a circular, outwardly expanding rash called erythema chronicum migrans (EM) , which gives the appearance of a bullseye. Patients may also experience flu-like symptoms, such as headache, muscle soreness, fever, malaise, fatigue, and depression. In most cases, the infection and its symptoms are eliminated by antibiotics, especially if the illness is treated early. Delayed or inadequate treatment can lead to more serious symptoms, which can be disabling and difficult to treat. Asymptomatic infections may occur, though this is the case in less than 7% of infected individuals in the United States. Asymptomatic infection may be more common in Europe.
Lyme Disease
Erythematous rash in the pattern of a "bull's-eye" from Lyme disease.
Left untreated, Borrelia bacteria begins to spread through the bloodstream within days to weeks after the onset of local infection, progressing symptoms to the joints, heart, and central nervous system. These symptoms include migrating pain in muscles, joints, and tendons; neck stiffness; sensitivity to light; and heart palpitations and dizziness caused by changes in heartbeat. Acute neurological problems, termed "neuroborreliosis", appear in 10–15% of untreated patients. EM may even develop at sites across the body that bear no relation to the original tick bite. Radiculoneuritis causes shooting pains that may interfere with sleep, as well as abnormal skin sensations. Mild encephalitis may lead to memory loss, sleep disturbances, or mood changes.
After several months, untreated or inadequately treated patients may go on to develop severe and chronic symptoms, including permanent paraplegia in the most extreme cases. Patients may develop Lyme arthritis, usually affecting the knees; nerve pain radiating out of the spine (Bannwarth syndrome); and shooting pains, numbness, and tingling in the hands or feet. A neurologic syndrome called Lyme encephalopathy is associated with subtle cognitive problems, such as difficulties with concentration and short-term memory. These patients may experience profound fatigue. Chronic encephalomyelitis can involve cognitive impairment, weakness in the legs, awkward gait, facial palsy, bladder problems, vertigo, and back pain. In rare cases, untreated Lyme disease may cause frank psychosis, which has been mis-diagnosed as schizophrenia or bipolar disorder. Panic attacks and anxiety can occur; as well as delusional behavior and detachment from themselves and reality.