Lyme disease is medically described as occurring in three phases, each with distinctive symptoms. The first phase is early localized disease, which occurs three to 30 days after the tick bite that transmitted the infection. This stage is characterized by skin inflammation. The rash that occurs is referred to as erythema migrans. It develops in about 70% of people who get Lyme disease. It starts at the site of the tick bite and expands over the next several days. It can eventually cover an area up to about 12 inches across. Some of the area may clear, giving the rash at times a bull's-eye appearance. The rash may feel warm to the touch, but it is usually not painful and does not itch. Some people get generalized symptoms in this stage as well, such as fever, chills, headache, muscle and joint pain, and swollen lymph nodes. Some people may have only the generalized symptoms without developing a rash.

The next stage of the illness is the early disseminated stage. In this stage, which occurs within days to weeks after the tick bite, there is spreading of the skin inflammation to other areas. Pain and swelling may develop in the large joints, such as the knee joints. Other symptoms that can occur include palsy of the facial nerve, leading to loss of muscle tone on one or both sides of the face. Meningitis may develop and cause headache and stiffness of the neck. Other possible symptoms include dizziness and heart palpitations.

If this condition is not treated, a later stage of the illness, known as the late disseminated stage, may develop in the following months to years. Symptoms of this later stage can include intermittent attacks of arthritis, with joint swelling and pain. Neurological symptoms, such as numbness and tingling in the extremities, shooting pains, and short-term memory problems have also been reported in the later stages.

Causes of Lyme disease

Lyme disease is a bacterial illness spread by a tick bite. In the United States, the disease is caused by the bacterial type Borrelia burgdorferi. In Europe, the bacteria Borrelia afzelii and Borrelia garinii also cause Lyme disease. Ticks frequently found on deer from various locations carry the bacteria in their stomachs and transmit it to humans when they bite.