Lyme disease has been reported from all continental states, except Alaska. High risk states are Connecticut, Delaware, Maine, Maryland, Massachusetts, Minnesota, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, Vermont, Virginia, and Wisconsin. States with moderate to high risk include District of Columbia, Illinois, Indiana, Iowa, North Dakota, and West Virginia.
The overall incidence of Lyme disease has increased in the USA. Latitude and population density are correlated with incidence, with states in the north seeing increases and southern states seeing stable or declining rates.
Lyme Disease is caused by bacteria belonging to the genus Borrelia transmitted through the bite of infected ticks belonging to the Ixodes genus. Borrelia burgdorferi is the predominant cause of the illness in North America, and Borrelia afzelii and Borrelia garinii in Europe and Asia. Ticks get infected when they feed on deer, birds, and rodents who are reservoirs for the bacteria and spread it to humans typically by nymphs (immature ticks). Due to climate change, tick populations are moving further north in latitude.
Lyme Disease is present in North America, Europe, and Asia. Travellers involved in outdoor activities in forested areas are at risk, including campers, hikers, and hunters. Brushing against vegetation or walking in city parks known to have infected ticks can also put a person at risk. Risk of Lyme Disease increases during the warmer months when ticks are most active, but they can be found year-round in areas where temperatures are above freezing.
Lyme Disease usually progresses in three stages. One of the first symptoms (for approximately 70-80% of persons) is a small bump and skin rash at the site of the bite which usually goes away after 1 or 2 days. After 3 to 30 days, the rash expands to an encircled red patch (known as Erythema migrans or Bull's Eye rash) which is warm to the touch but not painful or itchy. The rash may produce lesions. Other symptoms include fever, headache, muscle and joint pain, chills, fatigue, and swollen lymph nodes. Contact your healthcare practitioner immediately if you develop symptoms.
If untreated, the illness progresses to the second stage within days or weeks after exposure. Symptoms include severe headaches, meningitis, swollen joints, skin lesions, heart palpitations, dizziness, persistent fatigue, sleep disturbance, as well as loss of muscle tone in the face (Bell's palsy). Some of these symptoms usually disappear within weeks or months. However, if untreated, the illness will progress to a third stage which includes arthritis and chronic pain, numbness, tingling of hands and feet, and short-term memory loss.
Lyme Disease usually takes 2 to 4 weeks to treat if started promptly and includes taking antibiotics.
Travellers who hike, camp, or undertake outdoor activities in wooded regions or who frequent city parks of endemic areas should take measures to prevent tick bites.
There is no preventive vaccine or medication against Lyme Disease.
Borrelia bacteria images, life cycle, and distribution maps:
Information last updated: January 2020